摘要:

Journal of the Chemical Society,Faraday Transactions IISSN 0300-959Journal of the Chemical Society, Faraday Transactions ISUBJECT INDEX-VOLUME 72, 1976PAQBI, 1 AdsorptionAdsorption and Surface Reactivity of Metals by Secondary Ion Mass Spectrometry.Part 1 : Adsorption of Carbon Monoxide on Nickel and Copper. (Barber, Vickemanand Wolstenholme) . . . 40Adsorption Characteristics and the Thermal Stability of (Tlcx, ka)-A Zeoiite. (Nitta,Ogawa and Aomura) . . 2893Adsorption in Slit-like and Cylindricai Micropores in the Henry's Law Region. A Modeifor the Microporosity of Carbons. (Everett and Powl) . . . 619Adsorption of t-Butanol from Aqueous Solutions on a Polarized Mercury Electrode. (DeBattisti, Abd-El-Nabey and Trasatti) . . . . . . . 2076Adsorption of Water Vapour by Magnesium Fluoride.(Bairaclough and Hall) 610Chemisorption and Surface Structural Chemistry of Carbon Monoxide on Pt(ll0).(Comne and Lambert) . . . . . . 1659Clathration by parasubstituted Phenols. (jBarrei and Shanson) . 2348Confirmation of the Surface Structures of Goethite (a-FeOOH) and Phosphafed Gbethiteby Infrared Spectroscopy. (Parfitt, Russell and Farmer) . . . . 1032Development of Stepped Surface Regions on Polycrystalline Gold. Low Energy ElectronDiffraction and Auger Studies. (Isa. Joyner and Roberts) . , 540Electron Spin Resonance Study of Oxygen Adsorption on Thorium 'Oxide. (Bieysse,Electronic Spectra of Substituted Pyridines Adsorbed on 'Aluminas. (Knozinger andMiiller) . . . . . 2703Heats of Adsorption of Water Vapo& on NaX and KNaX Zeolite's at Different Tempera-tures. (Chuikina, Kiselev, Mineyeva and Muttik) 1345Hydroxyl Exchange on H-CaY and Pt/H-CaY Zeolites with Deuteiium.. (Dalia Be& andBoudart) . . 1723Infrared Spectroscopic Characteiization of 'the :-Alumina Surface. (Morteira, Ghiotti,Garrone and Boccuzzi) . 2722Infrared Study of the Adsorption of'Methy1 Fluorosulphaie Vapour on the SurfBce ofMagnesium Oxide. (Eley, Kiwanuka and Rochester) . . 876Investigation on the Surface Structure of Precipitated Silver Iodide Saniples 'by KryptonAdsorption. (Sidebottom, House and Jaycock) . . . 2709Isotopic Exchange Kinetics of Zinc Ions in Zn-A Zeolite. (Radak,'Gal and Saiai) . . 1150Location of Cations in Synthetic Zeolites X and Y.Part 4: Exchange Limiting Factors forCa2+ in Zeolite Y. (Costenoble, Mortier and Uytterhoeven) . 1877Molecular Theory of Adsorption in Pore Spaces. Part 2: Thermodynamic and MoiecularLattice Model Descriptions of Capillary Condensation. (Nicholson) . 29A New Isotherm for Multilayer Adsorption on Heterogeneous Surfaces. (Hsu, RudzinskiParticle Size of Wyoming Bentonite and its Relation to the Cation'Exchange Capacity andthe Homogeneity of the Charge Density. (Rengasamy, van Assche and Uytterhoeven) 376Potentiality of Photoelectron Spectroscopy in the Characterization of Surface Activity:Photoelectron and Infrared Spectroscopic Comparative Study of Pyridine Adsorptionon NH4-Y Zeolite activated at Various Temperatures. (Defosse and Canesson) .2565Reflectance Spectra of Surface States in Strontium Oxide and Barium Oxide. (Zecchina andStone) . . . . . . . 2364Redox Behaviour of Transition Metal Ions in Zeolites. Part 21 Kinktic Study of theReduction and Reoxidation of Silver-Y Zeolites. (Beyer, Jacobs and Uytterhoeven).Part 3 : Auto-reduction of Cupric Ions in Y Zeolites. (Jacobs, deWilde, Schoonheydt,Uytterhoeven and Beyer). Part 4: Kinetic Study of the Reduction and Re-oxidation ofCopper-Y Zeolites. (Jacobs, Tielen, Linart, Uytterhoeven and Beyer) 674, 1221, 2793Some Properties of Ammonium Exchanged Type L Zeolite. (Ono, Kaneko, Kogo,Takayanagi and Keii) . . . 2150Sorption of Water Vapour by Poiy-L-giuta&c Acid, Poiy-L-lysine and their Ssits and SomeChemically Modified Derivatives.(Rochester and Westerman) . 2753Study of Some Electron Transfer Reactions of Titanium Dioxide. (Davidson and Slater) 2416Szilard-Chalmers Cation Recoil Studies in Zeolites X and Y. Part 1 : Ion Exchange inZeolites X and Y. Part 2: Recoils from Open to Locked Sites. Part 3: Recoils fromLocked to Open Sites. (Lai and Rees) . . 1809, 1818, 1827Thermogravimetric Studies of Ion Exchanged Forms of'Zeoli& X and Y. (Lai and Rees) 1840Claude1 and Menaudeau) . . . . . . 1and Wojciechowski) . . . . . . 453Oxygen Anion Radicals on Zeolites. (Krzyianowski) ' . 15734 SUBJECT INDEX-VOLUME 72, 1976PAGETin Oxide Surfaces. Part 5 : An Infrared Study of the Reactions of Methylchlorosilanes withwith the Surface of Tin(Iv) Oxide. Part 6: An Infrared Study of the Reactions ofEthyl Isocyanate and Phenyl Isocyanate with Tin@) Oxide and MethylsilylatedTin(Iv) Oxide.Part 7: An Infrared Study of the Chemisorption and Oxidation ofOrganic Lewis Base Molecules on Tin(1v) Oxide. (Harrison and Thornton) 1310, 1317, 2484Transition Metal Ion Exchange in Zeolites. Part 1: Thermodynamics of Exchange ofHydrated Mn2+, Co2+ Ni2+ Cu2+ and Zn2+ Ions in Ammonium Mordenite.Part 2: Ammines of Co;+, Cu2$ and Zn2+ in Clinoptilolite, Mordenite and Phillipsite.(Barrer and Townsend) . . . . 661, 2650Vibrational Spectra of Molecules on Zeolites. Par't 1 : Acetylene on A-type Zeoiites. (Tam,Cooney and Curthoys). Part 2: Acetylene and Dimethylacetylene on X-type Zeolites.(Tam, Cooney and Curthoys). Part 3: Raman Spectra of Pyrazine on Zeolites X.(Tam and Cooney) .2577,2592, 2598Water in Ion-Exchanged L, A, 'X and Y kolitks : A' Heat' of Ikners'ion and Thermo-gravimetric Study. (Coughlan and Carroll) . . . . . . . 2016I, 2 Biophysical ChemistryArrhenius Plots of Complex Rate Parameters in Enzyme Kinetics. (Adams, Swart andVernon) . . . .Electron Spin Relaxat'ion and Fokier Transform Nuclear Magnetic Resonance Spectroscopyof Manganese(@ Complexes with Biomacromolecules. (Basasi, Laschi, Tiezzi andValensin) . . . . .Gravimetric Study of the Sorption of Water VapoG by Bovineserum Albumin. ' (Rochesterand Westerman) . . . . . . . . .One-Electron Reduction or a Ferrihaem. (Butler, Jayson and Swallaw) 'One-electron Reduction Reactions with Enzymes in Solution.A Pulse Radiolysis Stud;.(Bisby, Cundall, Redpath and Adams) .Phospholipid Monolayers at Non-polar Ojl/Water'Intekaces. ' Part' 1 : Phase Transitions &Distearoyl-lecithin Films at the n-Heptane Aqueous Sodium Chloride Interface. (Yue,Jackson, Taylor, Mingins and Pethica). Part 2: Dilute Monolayers of Saturated1 ,2-Diacyl-lecithins and -cephalins. (Taylor, Mingins and Pethica) 2685,Protein Hydration. Nuclear Magnetic Resonance Relaxation Studies of the State of Waterin Native Bovine Serum Albumin Solutions. (Oakes) . . .Protein-Surfactant Interactions. Spin Label Study of Interactions between Bovine SerudAlbumin (BSA) and Sodium Dodecyl Sulphate (SDS). (Laurie and Oakes) . .Proton Conduction in Protein Films. (Tregold, Sproule and McCanny) .Thermally Denatured Proteins : Nuclear Magnetic Resonance, Binding Isotherm andChemical Modification Studies of Thermally Denatured Bovine Serum Albumin.(Oakes) .. . .Thermally Denatured Proteins: Spin Label Studie's of Reversal of Thekal Aggregation ofBovine Serum Albumin (BSA). (Laurie and Oakes)Use of a Surfactant Selective Electrode in the Measuremeit of ;he Binding of AnionicSurfactants to Bovine Serum Albumin. (Rendall) . . . ..39715052498139151269421 61324509228268 1481I, 3 Catalysis (including heterogeneous and homogeneous catalysis and surface reactivity)Alkane and Cycloalkane Reactions on Rhodium, Rhodium-Copper and Related Films.Cyclopentane/Deuterium Exchange on Palladium-Gold and' PalladiumlTin Alloy Films.(Clarke and Taylor) .. 917Dynamc Investigation of t'he Mkchan'ism of Reaction betwekn Suiphur 'and Oxygen on aMolybdenum Surface by Means of Auger Electron Spectroscopy. (Kawai, Kunimori,Kondow, Onishi and Tamaru) . . . . 83 3Effects of Added Sugars on the Catalysis 'by Ckty1tr~meth;lammoniurn Bromide 'of theReaction between Hydroxide Ions and 2,4-Dinitrochlorobenzene. (Blandainer,Beatham, Branch and Reid) . . . . . . 2139Electron Donor Sites and Acid-Base Properties of Oxide 'Surfaces, as Studied by e.s.r.Spectroscopy. (Cordischi and Indovina) . . . . . . 2341Exchange Reactions of Benzene and Alkylbenzenes with beuterium on Alumina andMagnesium Oxide. (Scurrell and Kemball) . . . . . . . 818Exchange Reactions of CD2=CH-CH3, in the Absence of Gaseous Deuterium, overMagnesia and Rutile Investigated by Microwave Spectroscopy.(John, Kernball,Dickinson and Tyler) . . 1782Field Emission Study of Decomposiiion df &onia on -Individual 'Tungsten Planes.(Wilf and Folman) . . . 1165Heterogeneous Catalysis in'Solution. Part i 3 : Kinetics of Racemisation in Two IkisciblePhases with Rapid Exchange across the Interface, Illustrated by the Racemisation of(+)58pTris(ethylenediarnine) cobalt(@ Catalysed by a Carbon Black. (Totterdelland Spiro). Part 14: Kinetics of Isotopic Exchange Reactions in Two ImmisciblePhases with Rapid Exchange across the Interface. (Spiro and Totterdell) . 1477, 1485(Pkter and Clarke) . . . 120SUBJECT INDEX-VOLUME 72, 1976 5High Temperature Low Pressure Reactions of Oxygen with Tantalum as Studied by AugerElectron Spectroscopy and Line-of-sight Mass Spectrometry.(Pacia, Dumesic,Weber and Cassuto)Homogeneous Catalysis by Platin&(@-Tin(=) * Chlokde Complex. Part 4: EffectiveSpecies for Hydrogenation of Ethylene catalysed by [(CH3)4N]3[Pt(SnC13)5] in Acetone.Homogeneous Isotope Exchange Reactions, H2/Dz. (Pratt and Rogersj . . .Homogeneous Isotope Exchange Reactions, Part 2: CH4/D2. (Pratt and Rogers)Infrared Studies of a Ziegler Catalyst supported on Magnesium Oxide and TitanidInitial Oxidation of Molybdenum studied' by a High Resolution Auger-photoeiectroiInteraction of Carbon Monoxide with Platinum/Alumina and Platinum/Silica Catalysts':14C Carbon Monoxide Tracer Studies of Adsorption, Desorption and CatalystPoisoning.(Bain, Jackson, Thomson, Webb and Willocks)Interaction of Oxygen with Nickel Studied by Field Emission M'icroscopy. ' (Smiih andAnderson)Interactions of Butyl 'Alcohols with Fiash-Iliuminited Rutile'Surfaks. icundingham andMeriaudeau) . . . . .Isotopic Exchange Sfudies' and selective OAdation of 'Propene on Mixed Tin-AntimonyOxides. (Christie, Tayloi and McCain) . . .Laser-Raman Study of the Isomerization of Olefins over Alumina. (Turner; Paui, Reidand Hendra) . . . .Methanol Electro-oxidatioh Catalysts. Plafinum'momoted b y Tin. (McNicol, Short anh(Nowatari, Hirabayashi and Yasumori) . . . .Dioxide. (Eley, Keir and Rudham) . . .Spectrometer. (Nozoye, Matsumoto, Onishi and Tamura) . . .PAGE191927851589276916853892516123 114993342829Chapman) .. . . . 2735ham, Doyle and Samman) . . . 1495Photoeffects involving Oxygen-18 at Flash-iliuminated ZnO and TiOz Surkaces. (Cunning-Pyridine-induced Formation of 1702 Adsorbed' on Thermally Activated CaO. (Che,Reactions of 3,3-Dimethylbut-l-ene with Deuterium Oxide on Oxiie Catalysts. (Srkrrell,Mo!ler and Kemball) . . . . 2512Resistance Relaxation Studies of Gas/Metalkeac;ions leading to Simultaneous Dissolutionand Gasification. The Dissociated Oxygen/Tantalum System above 2000 K. Part 1 :Methodology and thz Role of Atomic Oxygen. Part 2: Mechanism, Kinetics and Ener-getics of Chemisorption Interface Crossing and Product Desorption. (Rosner,Chung and Feng) . 842,858Selective Oxidation of Propene'on Bismuih Mdlybda'te and Miied Oxides 'of Tin andAntimony and of Uranium and Antimony.(Pendleton and Taylor) 1114Studies of Heterogeneous Oxidation Catalysts. Part 1 : The Vanadium&) Oxide;Titanium(1v) Oxide System. Part 2: The Vanadium(v) Oxide+ Molybdenum(v1)Oxide and Other Binary Oxide Systems. (Cole, Cullis and Hucknall) . 2185, 2744Studies of Hydrogen Spillover. Part 1 : Study of the Rate, Extent and Products of HidrogenSpillover from Platinum to the Trioxide of Tungsten and Molybdenum. Part 2: Ti-tration of Hydrogen Adsorbed upon Silica Supported Platinum by Pent-l-ene.(SermonandBond) . . 730, 745Studies of Hydrogen Spillover. Par; 3: Citalysis of ;he Reduction of' Metal Oides bySupport Effects in the Break-up and Aggregation ojf Silve; F i i s under Catalytic' Conditions.(Riassian, T r i m and Williams) .. . 925Theoretical Studies of Polyelectrolyte "Catalysis'; of Ionic Reactions. Part 2: InterionicReactions between Similarly Charged Species. (Mita, Okubo and Ise) . . 1033Use of Labelled Propene to Distinguish between an Associative, a Dissociative and aConcerted Mechanism for the Double Bond Shift Reaction of Alkenes. (John,Marsden and Dickinson) . . . . . 2923Tench, Coluccia and Zecchina) . . . 1553Palladium on Silica. (Bond and Tripathi) * 933, 4 Colloid Science (including birefrigence, electrophoresis, light scattering, sedimentation,thixotropy, soluble and insoluble monolayers, micelles)Attachment of Particles to a Liquid Surface (Capillary Theory of Flotation). (Scheludko,Toshev and Bojadjiev) .. . . 2815Calculation of Molar Area of a Substance' at the Liquid/Vapour' Interface kom SurfaceTension and Energy of Evaporation. (Jain, Singh and Gombar) . . 1694Dispersion Interaction of Crossed Mica Cylinders : A Reanalysis of the IsraelachviliiTaborExperiments. (White, Israelachvili and Ninham) . . 2526Dynamic Dilational Surface Properties of Submicellar Multicomponent Surfact ant Soiutions.Part 1: Theoretical. (Garrett and Joos). Part 2: Thermodynamics of Adsorptionand Comparison with Experiment. (Garrett) . . 2161, 2174Interfacial Tensions at Alkane-Aqueous Electrolyte Interfaces. (Aveyaid and Saleem) 1609Meniscus Profiles between Concentric Cylinders. An Experimental and ComputationaiStudy.(Campanini, Swanson and Nicol) . . . . . . . . 2636 SUBJECT INDEX-VOLUME 72, 1976? A 1New Method for Measuring Surface Tension froni the Height of a Pendent Drop. (Levin,Pitts and Terry) . . . . . . . . 1519Permittivity Spectrum of Polystyrene-latex Suspensions.' (Williams and James) .. . 803Theory for the Equilibrium Contact Angle between a Gas, a Liquid and a Solid. (Jamesonand del Cerro) . . . . 883I, 5 Combustion and Flames (including explosions, shock waves; see also I, 8)Aspects of the Flame Chemistry of Cobalt. (Jensen and Jones) . . 2618Kinetics of the Thermal Unimolecular Reactions of Cyclohexane and kVinyicyclohexeneBehind Reflected Shock Waves. (Barnard, Parrott and Long) . 2404Thermal Unimolecular Decomposition of Ethyl Propionate behind Reflected Shock Waves.(Barnard, Cocks and Parrott) .. . . 1456I, 6 Diffusion (including transport processes, thermal diffusion, viscosity, thermal conductivity ;Diffusion Coefficients of Paraffins in a Graphon Membrane: the Early Time Procedure.(Ash, Barrer and Edge) . . . .Diffusion of SF6 in 13X Zeolite. (Ruthven'and Doetsch) 1Diffusion, Viscosity and Sedimentation of Poly(ethy1ene oxide) in Water. ' (Chew andCouper) . . .Effect of Ekctrolytes'on the Self:difTus'ion CoeffiGent of Water. (Tanaka)Effect of Pressure on the Diffusion Coefficient of Silver Ions in Molten Alkali'MetaiNitIates. (Cleaver and Herdlicka) .Examination of a Transference Number Anomaly: 0.02 mol dm-3 Aqueous Sod& Chlorideat 25°C.(Esteso, Chan and Spiro) .Flame Photometric Determinations of Diffusion Coefficients. ' Par; 5 : Rksults 'for &lciumHydroxide, Strontium Hydroxide, Barium Hydroxide and Copper. (Ashton andInterfacial Transfer s'tudied with a Rotating Diffusion 'Cell. . (Albery, Burke,. Leffler andHadgraft)Investigation of the Transport Propeities of a Quaternary kmmonium' Anion ExchangeMembrane. Part 2: Application of Irreversible Thermodynamics to the Iodide Form.Optimal Conditions and Measuring Functionals' in the Measurements' of Diffusion Cd-efficients. (Noszticzius, Liukkonen, Passiniemi and Rastas)Properties of Molten Carboxylates. Part 2: Viscosities of some Molten Lead and ZincCarboxylates. (Ekpe and Sime) . . .Relative Viscosities of Solutions of S o d i k add Poiassium Bromides and Iodides hDimethyl Sulphoxide at 25, 35 and 45°C.(Bicknell, Lawrence, Seeley, Feakins andWerblan) . . .Salt Permeation through an Ionic Membrane and a Te'st of Onsager Reciprocity. iFoleyand Meares) . . .Self-diffusion of n-Alkanes'in Type A Zeoliie. (Quig and Rees) 'Self-diffusion in Cyclohexane Single Crystals-A Re-appraisal. (Hampton and SheiwoodjSolvent Correction for Hittorf and Direct and Indirect Moving Boundary TransferenceMeasurements. (Gwyther, Spiro, Kay and Marx)Study of Ion-solvent Interactions in Formamidef Water Mixtures by thk Measurement ofViscosity of Sodium Chloride Solutions. (McDowall, Martinus and Vincent) . .Testing Intermolecular Potential Functions using Transport Property Data.Part 3 : BinaryDiffusion Coefficient of Methane+ Perfluoromethane. (Clifford, Dickinson, MatthewsTheory of Tracer Diffusion Measurements in Liquid Systems. (Liukkonen,' Passiniemi,Noszticzius and Rastas)Thermal Conductivities of Gaseous Aikanek Perfluoroalkane Mktures: (Ciifford,Dickinson and Gray)Thermal lsomerization of Ethyiidenecyclopropane and Methylmeihylenecyclopropane to2-Methylbuta-lY3-diene. (Clements and Frey) .Tracer Diffusion of Tritiated Heavy Water (DTO) in Heavy Water (DzOj und& Prekure. *(Woolf) .Viscosities of Oxygen' and Air oier a Wide Range- of Temperatures. (Matthews, Thomas;Duffy and Smith)Viscosity of Nitrogen and Ceiain Gaseois Mktures' at Low Tempeiatmei. (Gough',Matthews and Smith). . . .Volume Correction fcr Direct and Indirect Moving Boundary Transference Measurements:(Gwyther and Spiro) .. . . . . . .see also 11, 8)Hayhurst) . .(McCallum and Paterson) . . .and Smith) . . . .27771043382112118611425208161832325371144307110577123981419654291 72836199716371267238645141SUBJECT INDEX-VOLUME 72, 1976 7?&enI, 7 Electrochemistry (including electrolytes, activity coefficients, electrical conductivity,electrode processes)Acidic Dissociation Constants of Malonic Acid in 50 Mass Percent Ethylene Carbonate+Water from 20 to 55°C. (Hall6 and Bates) . . 2866Activity Coefficients of Single Complexes and Coordination Equilibria in'Thr&componentSystems of the Type MX2 + Solvent +Diluent. Systems involving CoC12, ZnCL,CuCI,, Pyridine, Benzene, Chlorobenzene and o-Dichlorobenzene. (LibuS, Kluczkow-ski, Klonkowski and Nierzwicki) .2552Behaviour of Oxalic Acid in the Anodic Oxidation' of Aiuminikn. 'The Role of AnodicallyInitiated Reduction Processes in Coloration and Photoluminescence. (Shimura) . 2248Behaviour of Triethyloxonium Hexachloroantimonate and Triethyloxonium Hexafluoroan-timonate in Dichloromethane Solvent. (Eley, Monk and Rochester) 1584Conductance of some Cobalt(m) Complexes in Water at 25°C. Part 1 : Conductance of Salktrans- and cis-Dinitrobis(ethy1enediamine)-cobalt(1n). Part 2 : Conductance of Salts ofEthylenediaminetet ra-acet at oco bal tate(m) . (Pet hybridge and Spiers) . . . 64, 73Conductance of Tetra-alkylammonium Perchlorates in Acetonitrile +Methanol MixturesConduction and Relaxation of Cations in Dehydrated Partially Copper(&)-exchangedSynthetic Faujasites.(Schoonheydt and Velghe) . . 172Conductivities of Alkali Metal Perchlorates in Ethylene Glycol * at 25°C. '(Fernkndez-Prini and Urrutia) . 637Coordination Equilibria and Aciivit y Coeffikents' in MC12 + isoquinoline + ChlorobknzeneSystems. (Uruska and Szpakowska) . . 2381Effects of Water on Proton Migration in Alcoholic Solvenk. Part 4: Conductance ofHydrogen Chloride in Butan-2-01 and in Ethanol at 25°C. (de Lisi, Goffredi andLiven) . . . . 436Electrical Double Layer Interaciions &der'Re&lation' by Surfaci Ionization' Equilibria-Dissimilar Amphoteric Surfaces. (Chan, Healy and White) .2844Electrochemistry of the H02 and 0, Radicals under Steady State Conditions. 'Part i : TheElectrochemistry of 0; at Neutral pH. Part 2: The Effect of pH over the Range 0.4 to11. (Airey and Sutton) . 2441,2452Electrophoretic Mobilities of 2iNa+, . 99Sri+ and 36Ci- Ions in 'Conintratkd AqueousSolutions of Some Inorganic 1 : 1,2: 1 , 1 : 2 and 2: 2 Salts and in Sea Water. (KniewaldandPuCar) . 987Further Correlations of the C'I"k3 Solvent 'Scale' for Halides witi for t'he SoivatedElectron. (Foxand Hayon) . . . . . . 1990HBr + (Bu)4NBr + H20 at 25°C. Application for Pitier's 'Equaiions. (Roy, Gibbons,Krueger and White) . . . . . 2197Hydration and Ion Pairing of Maieinates, Malonates, and Subitituted Malonates in AqueousSolution. (Klaning and (dsterby) 513Ionization Constants of Phenols in Methanol+ Water * Mixkres.' (Rocheste; andWilson) . . . . . . . . . . 2930Magneto-Optical Rotatory Dispersion Studies of Simple Electroiyte Solutions. Part 4:The Calculation of Partial Molal Magnetic Rotations and the Solvent Structure-Breaking Entropy Effects of Electrolytes. (Dawber) . . . . . 1738Non-equilibrium Thermodynamics of Electro-osmosis of Liquid Mixtures. Studies onAcetone+ Water Mixtures. (Srivastava and Abraham) . . . . . 2631Nuclear Magnetic Relaxation Study of Preferential Solvation in Diamagnetic ElectrolyteSolutions by Use of Magnetic Ion-Solvent Interactions. (Gill, Hertz and Tutsch) . 1559N.m.r. Study of the Self-Association of Ethyl and t-Butyl Alcohols in Nonpolar Solvents.(Fujiwara and Ikenoue) .. . 2375The Oxygen Electrode. Part 61 Oxigen Evoluiion A d Cbrrosibn at Iridium &odes.(Buckley and Burke). Part: 7: Influence of Some Electrical and Electrolyte Variableson the Charge Capacity of Iridium in the Anodic Region. (Buckley, Burke andMulcahy) . . . . 2431, 1896Raman Spectra of haIlik(1) Nitratk Solutions' in Liquid ' k o n i a . (Gardiner, Hajiand Straughan) . . . . . . . 93Re-determination of the Standaid Elekrode Potential of Zinc and Mean Molal ActivityCoefficients for Aqueous Zinc Chloride at 298.15 K. (Lutfullah, Dunsmore andPaterson) . 495Secondary Carbon-1 3' Isotope Effect on the Ionizakon of Be&oic Acid. iBayl&, Bron andPaul) . . . . 1546Shape of the Coexistence Curve and Elktricai Conductikty of Fused KN03+TlBrMixtures. (Ichikawa) .. 2257Solubility of Electrolytes in 1,2-DichlomethAe and 1 ,l:Dichioroethane, and Derivk FreeSolvation spectra. Part 51: Di-t-butyl Nitroxide as a Probe for Studying Water andat 25°C. (D'Aprano, Goffredi and Triolo) . . . . . 79Energies of Transfer. (Abraham and Danil de Namor) 955Aqueous Solutions. (Lim, Smith and Symons) . . . . . . . 2878 SUBJECT INDEX-VOLUME 72, 1976Solvent Coordination and Free Energies of Transfer of Cations in Dipole Aprotic Solvents.Spectroscopic Determination of Association Constank of * Water wit'h Organic 'Bases'.(Le Narvor, Gentric, Lauransan and Saumagne)Standard Potentials of the Silver-Silver Bromide Electrode in Propan-2-01; Wat& Mixtures'.Free Energies and Entropies of Transfer of Hydrobromic Acid.(Bose, Das andKundu) . .Theory of Electrolytes. P k t 1 : The Model of Polarisable Spheres. * (Berhetto-and SpitzerjVariable Temperature Proton Chemical Shifts of Aqueous Beryllium Salt Solutions.(Akitt and Duncan) .Variation of Electrical Conductivity with Composition in the System KNO,.+Ba(NO&at Constant Equivalent Volume. (Cleaver and Olteanu) .Washburn Numbers. Part 2: Alkali Metal Chlorides in the MethanoliWater andDioxan+ Water Systems; Sodium Halides in the Methanol+Water System. Results,Formal Relationships, Interpretation and Preferential Solvation. (Feakms, Khoo,Lorimer, OShaughnessy and Voice)X-Ray Photoelectron Spectroscopic Study 0; the Film Formed on a Gold Elecirode duringthe Electrochemical Reduction of Chromium(vI). (Dickinson, Povey and Sherwood)(Clune, Waghorne and Cox) .. .J, 8 Kinetics of Reaction (including photochemistry, reaction of gases, solids, liquids, twophase systems)Chain Initiation of Neopentane Pyrolysis and a Suggested Reconciliation of the Thermo-che+cally Calculated and Measured Rate Constants for the Recombination of t-ButylChemically Induced Dynamic Electron Polarization. Part 8 : Simultaneous Operations ofthe Radical-Pair and Photoexcited Triplet Mechanisms in the Photolysis of SubstitutedBenzoquinone, Naphthoquinone and Anthraquinone. (Adeleke and Wan) .Chemiluminescent Titration of F(g) with C(zs) and Microwave Production of AtomicCross Sections for Gas Phase Ion-Ion Rkcomdination in H30++X'+HX+H20 forDerivation of Activation Energies from Experiments 'on Chemical Adtivat ion of AlkilDuroquinone Triplet Reduction, in Cyclohexane, Ethanol' and 'Wate;, and by 'Durd-Electron Spin Resonance Evidence of the Photoionizatibn and Photoisomerization of FrekRadicals from y and Ultraviolet Irradiated Pyridinium Cations.(Quaegebeur,Flash Photolysis Studies of Benzophenone in Ethanol. (Colman, Dunni and h u h )Formation of Silylenes in the Thermolysis of Methylchlorodisilanes. (Davidson and Delf)Formation of Silylenes in the Thermolysis of Pentamethyldisilane and 1,l ,ZTrimethyl-disilane. (Davidson and Matthews) .Free Radical Addition to Olehs. Part 19 : Trifluoromethyl' Radical Addition to Fluoro;substituted Propenes and its Absolute Rate of Addition to Ethylene.Part 20: AReinvestigation of the Addition of Methyl Radicals to Fluoroethylenes. (LOW,Gas Phase Reaction between Iodine and Tetrkethylsilane.' P&t 1 : * Equilibriumand Thermochemistry. Part 2: Kinetics and the Bond Dissociation EnergyD(MesSiCH2-H). (Doncaster and Walsh). . . . . . 2901,Indicators in Benzene in the Presence of Dodecylammonium Propionate. (Nome, Changand Fendler) . . .Intermediates in the Nanosecond Pulse ' Radiolysis' of Dimet'hylaniline Solution inCyclohexane. (Zador, Warman and Hummel) .Isotopic Exchange Kinetics of Zinc Ions in Zn-A Zeolite. (Radak, Gai and SalaijKinetic Deuterium Isotope Effects in the Reactions of 4-Nitrophenylnitromethane withVarious Nitrogen Bases in Anisole.(Caldin, Parboo, Walker and Wilson) .Kinetic Electron Spin Resonance Spectroscopy. Part 5 : Effects of Chemically InducedDynamic Electron Polarization. (Ayscough, Lambert and Elliot) .Kinetic Isotope Effect in the Thermal Dissociation of Ethane. (Clark and Q h )Kinetic Isotope Effects and Tunnelling Corrections in the Proton-transfer Reactions betwEn4-Nitrophenylnitromethane and some Tertiary Amines in Aprotic Solvents. (CaldinKinetic Isotope Effects in the Reactions of 4-Nitrophenylnitromethane with various' Basesin Chlorobenzene. (Caldin, Parbhoo and Wilson) .Kinetic Study of the Reactions of Hydrogen and Oxygen Atoms wiih AGtone. ' (kbidge;Bradley and Whytock)Kinetic Study of the Reaction of Hyd;ogen'Atoms with Chloroflubrorn&hane'. (Biadley,Whytock and Zaleski) .. . . . . . . . . .Radicals. (Marshall, Purnell and Storey) . . . . . . .Fluorine. (Nordine and Rosner) . . . . .X=Cl, BR or I. (Burdett and Hayhurst) .Fluorides. (Cadman, Kirk and Trotman-Dickenson)hydroquinone. (Amouyal and Bensasson) . . . .Ofenberg, Lablache-Combier, Ronfard-Haret and Chachaty) . . .Tedder and Walton) . . . 1300,andMateo) . . . . . . . . . .PAGE129413291633210821321670266168685I799152624599612741432605191214031707290829 6136811501856177070611226451870228SUBJECT INDEX-VOLUME 72, 1976 9PAGEKinetic Study of the Reaction of Hydrogen Atoms with Hydrogen Chloride. (Ambidge,Bradley and Whytock) . . . 2143Kinetic Study of the Reaction of Hydrogen Atoms with Moieculai Chlbrine.' (Adbidge,Bradley and Whytock) . . . 1157Kinetics and Mechanism of Allene to Methylacetylene Isorneksation. (Walsh) . 2137Kinetics and Mechanism of Di-n-butylphosphoric Acid Transfer between Toluene andAqueous Phases. (Lyle and Smith) . . . . 1241Kinetics and Mechanism of the Reaction between Phenyiacetyiene and Tr~ethylaluminium+Tertiary Amine Complexes in Hydrocarbon Solution. (Allen and Lough) . 1124Kinetics and Thermodynamics of Decomposition of Barium Sulphate. (Mohazzabi andSearcy) . . . 290Kinetics of Activated Chemisorption, ' Part 1 : The Non-Elo&hia$ Pari of the Isoihem.Kinetics of Addition of Methyl and Ethyl Radicals to N i t k Okde. ' (Prait andVeltman) . . . . 2477Kinetics of Free Radical Chain 'Reac;ions in Solutions' of Tkh1o;oace;onitrile in Cyano-alkanes. Effect af Cyano-group Substitution on Metathetical Reactions.(Gonen,Horowitz and Rajbenbach) . . . . . . . . 901Kinetics of Glass Formation. (Ruckensteid and bun) . 764Kinetics of Hydrogen Isotope Exchange Reactions. Part 3i : p-Radiation-iiducedTritium Exchange in Mixture of Organic Solvents and Water. (Gold, McAdam andPross) . . . ... . . 755Kinetics of Reaction of Hydrogen Atoms with Ethylene. (Pratt and Veltmanj . . 1733Kinetics of Ternary Complex Formation between Nil1 Species and Pyridine-2-azo-p-dimethylaniline at High Pressure, by a Laser Temperature-Jump Method. (Grantand Wilson) . . 1362Kinetics of the Bromate-Iodidl and Iodate-Io&de Reactions 6y Ph-Stat 'Techniques.(Barton, Heng Nian Cheong and Smidt) 568Kinetics of the Gas-phase Reaction between Iodine A d Trichlo~osilane and the' BondKinetics of the Gas-phase Reaction between Iodine and Trimethylsilke and the BondKinetics of the Oxidation of Isopropanol by Aquavanadium(v) Ions in Aqueous PerchlorateMedia. (Wells and Nazer) .. . . . . 910Kinetics of the Oxidation of Octame~hylcy~lotetrasiloxane in the Gas Phase. (Davidsonand Thompson) . . 1088Mechanism of the Oxidation of Iron(r1) by the Az'ide Radicai. (Bkton'and Janovskf) . 1884Photocatalytic Oxidation of Propan-2-01 in the Liquid Phase by Rutile. (Cundall, Rudhamand Salim) . 1642Photochemical React& of Bifluorenylidene. Part 1 :' Steady Irradiatibn Inbestigations.(Vander Donckt, Toussaint, Van Vooren and Van Sinoy).Part 2: Flash PhotolyticInvestigations. (Van Sinoy and Vander Donckt) 2301, 2312Photochemical Studies of Rhodamine R.6G in Ethanol So1u;ions using Laser FlashPhoto-lysis. @ m e and Quinn). . 2289Photochemistry of 1,1,1-Trifluor~3-bromo'acetonee. (Maje;, Robb and Al-Saigh) ' . 1697Photoenolization of the ortha-Alkyl-substituted Acetophenones: Evidence for the EnoiTriplet State. (Findlay and Tchir) . . . . 1096Trans-Cis Photoisomerization of 14C-labelled '1,3-Diphenylpropenes. Part 1 : 'DirectPhotolysis. Part 2: Sensitized Photolysis. (Figuera and Serrano) . . . 1534,2265Photolysis of Bromotrichloromethane in the Presence of Dichloromethane, Difluoro-methane, Chlorofluoromethane and Dichlorofluoromethane.(Copp and Tedder) 1 177Photolysis of Nitrous Acid in the Presence of Acetaldehyde. (Cox, Derwent, Holtand Kerrj 2061Photo-Oxidation of Methane in the Presence of NO and NO. (Cox, Derwent, Holt andKerr) . . . . 2044Primary Processes in the 'Photolysis 'of Diazo-n-Propane and D'iazen-Butke. iAvila,Figuera, MenCndez and Pkrez) . 422Production of Chemically Activated 'Fluoioalkkes by Dirkct Fiuorination.' (Cahman,Kirk and Trotman-Dickenson) . . . . . 1428Quadrupole Ion Store (Quistor). Part 1 : Ion-molecule reactions in Methane, Water andQuenching of the Luminiscent State of the Uranyl Ion (UOq+) by Metal Idns. Evidence foran Electron Transfer Mechanism. (Burrows, Formosinho, Miguel and Coelho) . 163Radiation Mechanisms. Part 5 : Nitrite and Nitrate Ions in Aqueous Glasses. (Symonsand Zimmerman) 409Rates of Gas-phase Ionic Acetyiation' of some Alkylbenzenes by 'Acetyl Cations formedfrom Acetone and Butane-2,3-dione.(Chatfield and Bursey) . 417Reactions of Chlorine Atoms with Ethane, Propane, Isobutane, Fluoroethane, i,l-Difluoro-ethane, l,l,l-Trifluoroethane and Cyclopropane. (Cadman, Kirk and Trotman-Dickenson) . . . . . . . . . . . . . 1027(Aharoni and Ungarish) 400Dissociation Energy D(C13Si-H). (Walsh and Wells) . 1212Dissociation Energy D(Me3Si-H). (Walsh and Wells) . . . . 100Ammonia. (Lawson, Bonner, Mather, Todd and March) . 5410 SUBJECT INDEX-VOLUME 72, 1976PA01Reactions of Chlorine Oxide Radicals. Part 6: The Reaction O+C10+C1+02 from 220Reactions of Hydrogen Atoms in 6 mol dm-3 Sulphukc Acid.Part 2: Thi Transitionfrom Activation to Diffusion Control. (Dainton, Holt, Philipson and filling) . 257Reactions of iso-Propyl Radicals with Oxygen, Hydrogen and Deuterium. (Baldwin,Cleugh and Walker) . . 1715Reaction of Nitrosomethane and of T;ifluoronitrosome;hane 'with Nitric' Oxide. (Christieand Matthews) . . 1652Reactions of the Negative 'Oxygen Ion (O-:) with Carbonyl 'Compounds. (Harrison andJennings) . . 1601Relative Rate Constants for the Reactions df OH' Radicals Gith Hz, CH4, CO, NO andHONO at Atmospheric Pressure and 296 K. (Cox, Derwent and Holt) . . 2031Simple Model for Second Virial Coefficients which includes Angular Coordinates. Cal-culation of Second Virial Coefficients for Hydrocarbons and Their Mixtures.(Okamotoand Wood) 2492Single-pulse Shock Tube Studies of 'HydrLcarbon Pyrolysi's. Part 5:' The 'Pyrolysis ofNeopentane. Part 6 : The Pyrolysis of Isobutene. (Bradley and West) . . . 8,558Solvent Effects on the Kinetics and Thermodynamics of the Fast Proton-transfer Reactionsof Trichloroacetic Acid and Picric Acid with Phenyl Diethyl Nile Blue Base in AproticSolvents. (Burfoot and Cald!n) . . 963Study of the Spectra and Recombination Kinetics of Alkyl Radicals by Molecular .Modu-lation Spectrometiy. Part 1 : The Spectrometer and a Study of Methyl Recombmationbetween 250 and 450 K and Perdeutero Methyl Recombination at Room Temperature.(Parkes, Paul and Quinn). Part 2: The Recombination of Ethyl, Isopropyl andt-Butyl Radicals at Room Temperature and t-Butyl Radicals between 250 and 450 K.(Parkes and Quinn) .1935, 1952Triplet Exicted States of 1,4-disubstituted Akthraquinones: Possible Evidence' for Associa-tion of Quinones in Solution. (Land, McAlpine, Sinclair and Truscott) . . 2091Two Photon Laser Photolysis of Toluene. (Beck and Thomas) . . 2610Wavelength Dependence of the Fluorescence Quantum Yield of Some Substituied Phenols.ta 426 K. (Clyne and Nip) . . 2211(Kohler and Getoff) . . . . . . . . 2101I, 9 Polymers and Polymerization (including physical properties of polymers and their solutions)Absolute Prediction of Upper and Lower Critical Solution Temperatures in PolymerSolutions from Corresponding States Theory : A Semi-empirical Approach. (Cowieand McEwen) .. .Degradation of Poly(viny1idene chloride) in Solution. Part 2: A Conductivity 'Study in theHexamethylphosphoramide+Tetramethylene Sulphoxide System. (Davies) . .Effects of Zinc Chloride on Polymerisations Initiated by Benzoyl Peroxide. (Bevingtonand Dyball)Gegenion Binding in Aqueous' Solutions ' of Tetra-alkyla&unonkm Polyair ylates andInfluence of Microstructure on the Upper and Lower Critical Soiution Temkratures ofInfluence of Solvent on the Conformation of Polymers Adsorbkd at'the Solid-LiquidManganese Pentacarbonyl Chloride as a Thermal Initiator of Free Radical Po1;merization.Moderated Copolymerization A d iis Applications. * The Transfer React& &tweenStyryl Radicals and Carbon Tetrabromide. (Bamford)Photoinitiation of Free-radical Polymerization by Transition Metal Carbonyls in Systemswithout Halides.(Bamford and Mullik)Solute Diffusion in Polymer Networks. Part 5 : H;drox;ethjl&llulose Gels; Solven'tEffects and Fluorescence Depolarisation Measurements. prawn, Kloow, ChitumboSteric Stabilization in Polymer Melts. (Smitham and Napper) .Poly(styrene-su1phonate)s. (Mita, Okubo and Ise) . . .Interface. (Clark, Robb and. Smith) . . . . . .Kinetics of Emulsion Polymerization. (Weiss and Dishon) . . . . .(Bamford and Mullik) . .Poly(methylmethacry1ate) Solutions. (Cowie and McEwan)andAmu) . . . . . . . . .16752390980162752614891342221 828053684852425I, 10 Radiolysis (including nuclear transformation in solids, neutron capture, etc.)Electrcn Spin Resonance Studies of Elementary Processes in Radiation- and Photo-Chemistry.Part 13 : Radiolysis of Solutions containing Maleamic Acids and Male-imides. (Ayscough and Elliot) . . . 791Electron Transfer and Addition Reactions of Free Nitroiyl Radical's with RadiationInduced Radicals. (Nigam, Asmus and Willson) 2324Excitation Energy Transfer in Clathrates. (Guarino, Occhiuki, PbssaGo and Basianelli) 1848Low Temperature Pulse Radiolysis of Concentrated Aqueous Solutions. Evidence forTrap-to-Trap Tunnelling in Sol50 v/v Ethylene Glycol+ Water and 10 mol dm-3 OH-aqueous solutions. (Buxton and Kemsley) . . . . . . . . 46S U B J E C T INDEX-VOLUME 72, 1976Mechanism of Tryptophan Oxidation by Some Inorganic Radical-Anions : A PulseRadiolysis Study.(Posener, Adams, Wardman and Cundall) .Oneelectron Reduction Potentials of Substituted Nitroimidazoles measured by PulseRadiolysis. (Wardman and Clarke)Pulse Radiolysis Study of Monovalent Cadmium, Cobalt, Nickei and ' Zinc 'in AiueouiSolution. Part 2: Reactions of the Monovalent Ions. (Buxton, Sellers andMcCracken) . .Pulse Radiolysis Study of s'ome Radical Proionation Reactions. (kkaifis and Sellers) .Radiation Induced Dechlorination of 1 ,2-Dichloroethane and Determination of ArrheniusParameters for Hydrogen Atom Abstraction from Chloroethanes by the QclohexylRadical. (Katz, Baruch and Rajbenbach)Radiation Induced Dechlorination of 1,1,2-Trichloroe~hane.' R&ctions of i,2-DidhloroLethyl Radicals. (Katz, Baruch and Rajbenbach) ..Radiation Mechanisms. Part 12: E.s.r. Studies of Electron &pture by Silver&) Ions,Nitrate Ions and their Ion Pairs and Clusters in Methyl Cyanide. (Brown, Findlay andS ymons)Radiolysis of 'Carboxylic' Compounds. Part 2: Radiolysis of Liquid Acetic. Acid.(JosimoviC, Teply and Mikik) . . . . . . . .I, 11 Solid-state ChemistryDislocations in Pyrene Crystals. (Hooper and Sherwood) .Effect of Structure on the Heats of Formation of Solid Solutions ofCsCl'with Other'AlkaiiElectrical Conductivity as a Defect Property of yFeOOH. (Kaneko and Inouye) . .Electron Tunnelling in Aqueous LiCl at Low Temperatures. Evidence for Tunnelling viaDeep and Shallow Traps. (Buxton and Kemsley) . ."Interstitial" Quasi-Lattice Model for Ion-Molecule Associations in Molten' Salts:(Sacchetto, Bombi and Mac&) .. .Kinetics and Thermodynamics of Decomposition of Barium Carbonate. (Basu and Larcy)Lattice Energies and Thermodynamic Parameters for Salts having Octahedral Anions :Rubidium Hexachlorostannate, RbzSnCls and Rubidium Hexachlorotellurate,Rb2TeC16. (Jenkins and Smith) .Low Frequency Dielectric Dispersions in the Peryiene + Chloranil Charge'Transfer Complex.(Carnochan and Pethig) . .Paramagnetism and Semiconducky in Organic h-n* Molecular Complexes. * (Munnochand Wright) . .Properties of Molten Carboxylates. Part 3 :' Electkd Conductance, Density and Viscosityof some Molten Cadmium Carboxylates. (Adeosun, Sime and Sime)Proton Mobility in Solids. Part 5: Further Study of Proton Motion in DecationatedNear-faujasite H-sieves by Pulse Nuclear Magnetic Resonance.(Mestdagh, Stoneand Fripiat) .Secondary Crystallization of Poiy(Tetiamethy1ene Oxide). (Warner, Biown and Wetton)Terminal Solid Solubility of Hydrogen in the Zirconium-2.5 weight % Niobium Alloy.Thermochemical Propertie; of 'Ammonium Exchanged Type Omega 'Zeoli;e. (Weeks,Halides. (Shukla, Ahluwalia and Rao) . . .(Sinha) . . * .Kimak, Bujalski and Bolton) . . . .1 1PAGE223 1137714647992462190317922852872128812581333197218893532355198124701541064134575I, 12 Thermodynamic and Equilibrium Properties (including multiphase systems)Accurate Thermodynamic Analysis of the Rate Constants of Solvolysis of t-Butyl Chloridein t-Butanol.An unexpectedly High Negative Value of the Heat Capacity of Acti-vation. (Viana, Gonqalves and da Costa Campos) . 1541Aqueous Solutions containing Amino-acids and Peptides. Part 2: Gibbs Fkction andEnthalpy Behaviour of the Systems Urea + Glycine, Urea + a-Alanine, Urea + a-Aminobutyric Acid and Urea + Glycylglycine at 298.15K. Part 3: The OsmoticCoefficient at the Freezing Temperature of the Solutions of Aqueous Systems containingGlycine and some Alkali Metal Chlorides and some Tetra-alkylammonium Bromides(Lilley and Scott) . . . . . 184, 197Atomization Energies of Gaseous AI2Pd and AlPd. 268t-Butylcyclohexane as an Inert Solvent in n.m.r. Studies of Hydrogen Bonding. (Soon N& 1101Critical Properties of Binary Mixtures.(Hicks and Young) . 122Depression of the Freezing Point to Lithium by Nitrogen and by Hydrogeh. EutecticCompositions and Solid Solubilities. (Hubberstey, Pulham and Thunder) . . 431Derivation of Thermodynamic Functions of Ionization from Acidic Dissociation Constants.The Sigma Pest Method vis4-vis Polynomial Regression Procedures. Oves and Moseley) 1 132Equation of State for all Phases. Part 1 : Basic Isothermal Equation. (Seibold) . 273Excited States of Naphthols. Part 2: Molecular Orbital Calculations on SubstitutedNaphthols. (Rosenberg and Brinn) . . . . . . . . 448(Cocke, 'Gingerich and Chang12 SUBJECT INDEX-VOLUME 76, 1976Extension of Everett and Penney's Measurements of the Thermodynamics of the SystemBenzenefBiphenyl at 288.1 K.(Allen, Holmes and Walsh) .Heat of Dilution of Aqueous Solutions of Sodium Salts of Partially Sulphonated Pol+-styrenes. (Mjta, Okubo and Ise) .Heats of Adsorption of Water Vapour on NaX' and 'KNaX Zeolites at Different' Tern'-peratures. (Chuikina, Kiselev, Mineyeva and Muttik) . .Hydration-Dehydration Constants of a,a,a-Trifluoroacetophenone by Spectral andElectrochemical Methods. (Scott and Zuman) .Hydrogen Bonding in some Adducts of Oxygen Bases with Acids. Part 8; Proton ChemicalShifts and Thermodynamic Data on the Association of Chloroacetic Acids with SomeOxygen Bases. (HadZi and Smerkolj) .Ionic Solvation in Water+ Co-solvent Mixtures. Par; 4: Free Energiks of 'Transfer 0;Single Ions from Water into Waterft-Butyl Alcohol Mixtures. (Wells) .Isentropic Apparent Molal Compressibilities and Compressibilities of Ionization ofCarboxylic Acids in Aqueous Solution.(Hsiland and Vikingstad)Melting of Group VI Transition Metal Hexacarbonyls : Thermodynamic 'Parameters:(Fabbrizzi, Mascherini and Paoletti)Nuclear Magnetic Resonance Line Shape knalysis by the Method of "on-iinear' LeastSquares. (Moore)Oxygen-1 8 and Deuterium'lsotope Effect on the Freezing Point of Diluie Water + DioxanPhase Diagram and n.m.r. Study of the Lyotropic Liquid Crystalline Phases formed byLithium Perfluoro-octanoate and Water. (Everiss, Tiddy and Wheeler)Physicochemical Studies of Super-cooled Liquids. Cyclic Carbonates and a/3-UnsaturatedAldehydes. (Masood, Pethrick and Swinton)Possible Five-Coordination of the Copper(r1) Ion.The CuClz + Monodentaie Aromati;Amine (Isoquinoline) +Diluent (Chlorobenzene) System. (Uruska and Szpakowska)Resolution of the Far Ultraviolet Absorption Bands of Solvated Iodide. (Barker, Fox,Walton and Hayon) . . .Self-heating in the Decomposition of 3:Methyl-3-chlorodiazirh1e : Determination 0.fReaction Exothermicity and Correction of Arrhenius Parameters. (Archer andSolid and Liquid Crystalline Phases in t'he Sodium Dodecyl Suiphatej Hexadecanoic Acid < Water System. (McDonald and Peel) .Solubility of Long-chain n-Paraffins in Pentane and Heptane. (Madsen. and Boistelle)Solubility of Oxygen in Some Water+Alcohol Systems. (Cargill) .Solute Interactions in Dilute Aqueous Solutions. Part 1 : Microcalorimetric Study'of theHydrophobic Interaction.(Franks, Ped!ey and Reid) .Solvation of Tetrabutylammoniii Bromide in Water I- Acetonitriie Mixtures 'at 298.15 Kfrom Vapour Pressure Measurements of Dilute Solutions. (Treiner, Tzias, Chemla andStudies in Ion So1vat;on in Non-aqueous Solvents and 'their Aqueous Mixtures. Part 18:Enthalpies of Transfer of Alkali-metal Halides from Water to Dioxanf Water Mixtures ;Structural Effects and Comparison with Large Ions. (Feakins and Allan) .Thermodynamic Functions of Hydration of Alkali Metal and Halide Ions. (Jalenti andCaramazza)Thermodynamic Study of' the Deuteiium Isotope Effect in Hydrogen-bonded Systems.(Handa, Mattingley and Fenby) .Thermodynamic Study of the Linde Sieve '5A+ Ethane System. . (Richards, * Stroud andParsonage)Thermodynamic Study of the Linde' Sieve 5Ak Met'hane 'System. (Stroud, Richards;Limcharoen and Parsonage) ..Thermodynamics of the Systems NO; ='NO;ffO; and' NO,ktO:- = NO;<O; inThreshold Energy in the Abstraction Reaction between Hydrogen Atoms and Propane..,\-Transition in AgNO, at High Pressures. (Klement)Vapour-Liquid Equilibria. Ternary Non-Electrolyte Mixtures wiih Two l[l;volatileComponents : Squalane and Dinonyl Phthalate. (Ashworth and Hooker)Vapour Pressure and Enthalpy of Sublimation of 1 ,3,5,7-Tetranitro-lY3,5,j-tetra~azacyclo-octane (HMX). (Taylor and Crookes)Vapour Pressure Isotope Effects in Aqueous Systems. Part 7: The System ['HiIPyrihinef[2Hs]Pyridine+Hz0. (Chan and Van Hook) .Vapour Pressure Studies of Simple Hydrogen Sulphate Salts in khydious ktric Acid atVapour Pressures of Solid Benzene, Cyclohexane and Their Mixturks.(Ha, Morrison andRichards). .Viscosity of Aqueous Solkons of TINO;, TlzS04 and TiOH at 25'C. (Martinus andVincent) . . . . . . ..Solutions. (Jancso, Illy and Staschewski) . . . .Tyler) . .Poltoratskii) . . . . .Molten Alkali Nitrates. (Paniccia and Zambonin) . . .(Bayrakceken, Vidaud, Fink and Nicholas) . . . . . . . .0°C. (Dawber) . . . .PAGE5345041345119211886011441896826220317472025453441448227410782296359200731471 51355175994215121058303224072358321251051250AUTHOR INDEX-VOLUME 72, 1976PAGE PAGEAM-El-Nabey, Beshier A. . . . 2076 Bonner, Ronald F.. . . 545Adams, Paul A. . . . . . 397 Branch, Charles H. . . . . 2139Adeleke, B. B. . . . . . 1799 Breysse, M. . . . . . 1Abraham, M. George . . . . 2631 Bose, Kumardev . . . . 1633Abraham,MichaelH. . . . 955 Boudart, M. . 1723Adams, Gerald E. . . . j l , 2231 Bradley, John N. 8,558,1157, 18i0,2143, 2284Adeosun, Samuel 0. . . . . 2470 Brinn, Ira Mark . . . . 448Aharoni, Chaim . . . . . 400 Bron, Jan . . . . 1546Ahluwalia, J. C. . . . . 1288 Brown, D. Robert' . . . . 1792Airey, Peter L. . . . . 2441, 2452 Brown, D. S. . . . . . 1064Akitt, J. W. . . . . . 2132 Brown, W. . . . . . 485Albery, W. John . . . . 1618 Buckley, Denis N. . . 1896, 2431AIkaitis, Saulius A. . . . . 799 Bujalski, Robert L. . . . . 575Allen, Geoffrey . . . 534 Burfoot, G.D. . . . . , 963Allen, Peter E. M: . . . 1124 Burke,JamesF. . . . 1618Al-Saigh, Z. Y. . . 1697 Burke, Laurence D. . . : 1896,2431Ambidge, Peter F. . 1 1157, 18i0, 2143 Burrows, Hugh D. . . . . 163Amouyal, E. . . . . . 1274 Bursey, Maurice M. . . . . 417Amu, T. . . 485 Butler, John 1391Anderson, John S.' . . 1231 Buxton, George V: : 466, 1333, 1484,1884Aomura, Kazuo . . . 2893Archer, (Mrs) Wendy H. : . 1448 Cadman,P. . . 996, 1027, 1428Ash, Richard . . : . 2777 Caldin, Edward F. . li2, 963, 1856, 2645Ashworth, Anthony J. . . . 2240 Campos,M. V, da Costa . . . 1541Asmus, Klaus-Dieter . . . . 2324 Canesson, Paul . . . . . 2565Aveyard, Robert . . . . . 1609 Caramazza, Raffaele . . . . 715~yscough, Peter B. : . . 791,1770 Carnochan, Paul .. . . . 2355Carroll, William M. . . . 2016Bain,FrancesT. . . . . . 2516 Cassuto, Albert . . . , . 1919Baldwin, Roy R. . * . 1715 Chachaty, C. . . . . . 143Bamford, Clement H. . . 368, 221'8,2805 Chan, Chee-Yan . . . . . 1425Barber,Michael . . . . . 40 Chan,Derek . . . . . 2844Barker, B. E. . 344 Chan, T. C. . . . . 583Barraclough, Peter B. . 610 Chang, Shuya A. . , . . 296Barrer, Richard M. . 661,23~8,26~0,2777 Chapman, Alan G. . . . 2735AlIan, Christopher T. . . . . 314 Burdett, Nigel A. . . . . 245Ashton, Anthony F. . . . . 208 Campanini, R. . . . . 2638Avila, Maria J. . . 422 Cargill,Robert W. . . . . 2296Barnard, John A. : 1 14;6,2404 Chang, Chin-An. : . . . . 268Baruch, G. . . . . : 1963,2462 Che, Michel . . . . . 1553Barton, Allan F.M. . . 568 Chatfield, Dale A. . . . . 417Basosi, Ricardo . . . . . 1505 Chemla, Marius . . . . . 2007Bassanelli, R. . . . . 1848 Chew, B. . . . . 382Basu, Tushar Kanii . . . . 1889 Chitumbo, K. : . . . . 485Bates, Roger G. . . . . 2866 Christie, James R. . . . . 334Bayles, John W. . . . . . 1546 Christie, Margaret I. . . . . 1652Bayrakceken, Fuat . . . 1058 Chuikina, V. K. . . 1345Beatham, GeffreyH. . . . 2139 Chug, H. M. . . : ; 842, 858Beck,Gerhard . . . . . 2610 Clark, Alec T. . . . . . 1489Bennett0,H.P. . . . . . 2108 Clark, J. A. . . . . . 706Bensasson, R. . . . . 1274 Clarke,EricD. 1377Bevington, John C. . . 980 Clarke, John K. A. 1 9i7,1201Beyer, HermaM . . 6i4, 12il,2793 Claudel, B. 0 . 1Bicknell, R. T. M. . . . 307 Cleaver, Brian .. 16j0, 1861Bisby, R. H. . . . 51 Clements, Allan D. . . . . 1637Blandamer, Michael J. . . 2139 Cleugh Christopher J. . 1715Boccuzzi, Flora . I . . . 2722 Clifford, Anthony A. . 1997,2917Bolton, Anthony P. . . 575 Cocke, DavidL. . . 268Bombi, G. Giorgio . . 1972 Cocks, Alan T. . . . 1456Bond, Geoffrey C. . . '730, j45, 933 Coelho, F. Pinto . . 16313Boistelle, R. . . . . . 1078 Clune, Gerard . . . 1294Bojadjiev, D. T. . . 2815 Clyne, Michael A. A. . . . 22114 AUTHOR INDEX- VOLUME 72, 1976PAGE . . . 2185, 2744 . . . 2605. 1553 . . 1659. 1177 . . . 2341. . . 1877 . . . 2016382526, 16751294 : 20j1, 2044, 2061723* 2185, 2744 : 51, 1642, 2231. 1495, 1499. 2577, 2592. . 2~7'7,2592,2598PAGE. 1105 . 1165163344, 1990.359. 1637. 154. 2375Cole, David J. .Colman, P.Coluccia, SalvatoriComrie, C. M. .Cooney, Ralph P.Copp, David E. .Cordischi, Dante.Costencible, Martin L.Coughlin, BrendanCouper, A,.Cowie, John M. G.Cox, Brian G. .Cox, Richard A. .Crookes, Roy J. .Cullis, Charles F.Cundall, Robert B.Cunningham, JosephCurthoys, GeoffreyFoiey, T. .Folman, M.Formosinho, SebastiacFox, Malcolm F.Franks, Felix .Frey, Henry M. .Fripiat, J. 9.Fujiwara, Hideaki'Gal, Ivan J.Gardiner, Derek J.Garrett, Peter R.Garrone, EdoardoGentric, Emilie .Ghiotti, GiovannaGibbons, James J.Gill, D. S.Gingerich, Karl A:Goffredi, Mario .Gold, Victor .Gombar, Vijay .Gonqalves, Raquel M.Gonen (Geliebter), Y.Gough, David W.Grant, Michael W.Gray, Peter .Guarino, A.Gwyther, John R.Ha, H..Hadgraft, JonathanHad&, D. .Haji, Ali H. .Hall, Peter G. .HallC, J. C.Harnpton, Eric M:Handa,Y. P. .Harrison, Alex G.Harrison, Philip G.Hayhurst, Allan N.Hayon, E. .Healy, Thomas W.Hendra, Patrick J.Heng, Nian CheongHerdlicka, ConstanfaHertz, H. G. .Hicks, Colin P. .Hirobayashi, KazuoHbiland, Harald .Holmes, Paul .Holt, B. J. .Holt, Pauline M.Hooker, David M.Hooper, Robert M.Horowitz, A.House, William A:Hsu, C. C. .Hubberstey, Peter'Hucknall, David J.Hummel, AndriesIchikawa, KazuhikoIhm, s. K. .Ikenoue, Tsuneo .Illy, Hddy .Indovina, ValerioTnouye, Katsuya .Isa, Saadoon A. .he, Norio . .1 J.. 1150932161,2174.2722. 1329. 2722. 2197. 1559. 26879,436. 755. 1694. 1541. 901. 645 . 1362. 19971848. 1051. 1618 . 1188 . 93. 610. 2866. 2398. 13551601208, 245344, 1990. 2844. 2829. 568. 1861. 1559. 122 . 2785. 1441. 5342572044, 2061 . 224014io,i41913 i 7,2484Dainton, Frederick S.Dalla Betta, R. A.Danil de Namor, AngeD'Aprano, AlessandroDas, AsimK. .Davidson, Iain M. T.Davidson, R. StephenDavies, Donald H.Dawber, John G.De Battisti, AchilleDefosse, Camille.del Cerro, M. C. G.Delf, Michael E..de Lisi, RosarioDerwent, Richard G.de Wilde, Willy .Dickinson, EricDickinson, RonaldDickinson, ThomasDishon, MenachemDoetsch, Ingo H.Doncaster, Alan M.Doyle, B..Duffy, A. N. .Dumesic? James A.Duncan, Robert H.Dunne, Adrian .Dunsmore, Helen S.Dyball, Christopher J.. . . . 257 . . . 1723:la F. . . 955. 79 . . 1633 . . 1088, 1403, 1912. 2416 . . 2390 . 1738, 2125 . 2076i a C.. . . . 2565 . . . 883 . . . 1912 . . 436 . . 2031,2044,20611221 : 1997, 2917 . . . 1782, 2923. 686. 1342 . . . 1043. 2901, 2908. 1495 . 238. 191921 322289, 2605 . . . 495. 98013i0,Edge, A. Vernon .Ekpe, Udofot J. .Hey, Daniel D. .Elliot, A. John .Esteso, Miguel A.Everett, Douglas H.Everiss, Ethna .. . . . 2777 . . 1144 . . 876, 1584, 1685 . . 791, 1770. 1425203 1,. 2872 . 901 . 2709 . . . 619. 1747 . 45343 12185, 2744 . 1368Fabbrizzi, Luigi .Farmer, Victor C.Feakins, David .Fenby, D.V. .Fendler, Janos H.Feng,H.H. .Fernandez-Prini, R.Figuera, Juan M.Findlay, David M.Findlay, Tristan J. V.Fink, Richard D.. . . . 8961082 : 307, 3i4, 2661 . * 1355 . . 296 . . . 842, 858637422, 1534, 2265 . . . 1096. 1792. 1059. 2257. 764. 2375 . 2203. 2341. 12585401033, 1627 504AUTHOR INDEX- VOLUME 72, 1976 15PAGEIsraelachvili, Jacob N. . . . . 2526Ives, D. J. G. . . . . . 1132Jackson, Craig M. . .Jackson, SamuelD. . .Jacobs, Peter A. . . ,Jain, Dharam V. S. . .Jalenti, Roberto . . .James, Arthur M. . .Jameson, G. J. . . .Jancso, Ghbor . . .Janovskf, Igor . .Jaycock, MichaelJ. . .Jayson, Gerald G.Jenkins, Harry Donald BrookeJennings, Keith R. . .Jensen, David E. . .John, Christopher S.. .Jones, George A.Joos, Paul . . .Josimovik, L. J.Joyner, Richard W.. . 2685251 66i4, lGl, 2793 . . 1694 . . 715. . 803 . . 883 . . 2203 . . 1884 . 2709 . 1391 . . 353 . 16012618 : 1782, 2923. 2618. 2161. 285. 540Kaneko, Katsumi . . 1258Kaneko, Masamichi . 21 50Katz,M.G. . 1903, 2462Kawai, T. . . 833Kay, Robert L. . . . . . 1419Keir, Douglas A. 1685Kemball, Charles . : 81'8, 1782, 2512Kemsley, Kenneth G. . . 466, 1333Kerr, J. Alistair . . . 2044,2061Khoo,KeanH. . . . 2661Kimak, Diane G. 575Kirk, A. W. . : 996, 1027, 1428Kiselev, A. V. . 1345Kiwanuka, GeraldM. : . . 876Klaning, Ulrik K. . . . 513Klement Jr., William . . . 303Klonkowski, Andrzej . . 2552Kloow, G. . . 485Kluczkowski, Marek .2552Kniewald, Zlatko . . 987Wzinger, Helmut . . . . 2703Kogo, Kazutoshi . . . . 2150Kondow, T. . . . . . 8 3 3Krueger, Charles . . . 2197Kundu, Kiron K. . . . . . 1633Kunimori, K. . . . . . 833Lablache-Combier, A. . 143Lambert, Graham . . . 1770Lambert, R. M. . . . . 1659Land, Edward J. . . 2091Laschi, Franco . . . . 1505Lauransan, Jacques . 1329Laurie, Olive . : 1324, 2681Lawrence, Kenneth G. . . 307Leffler, Esther B. . 1618Le Narvor, Anne . . 1329Levin, P. F. . . 1519Libub, Wodzimierz : 2552Lilley, Terence H. . 1 i84, 197Lim, Yan Y. . 2876Limcharoen, Preedeeporn 1 . 942Keii, Tominagi . . . . 2150Krzyifanowski, Stanishw . . 1573Lai, Pin Pah . . 186, 181'8,i8i7,1840Lawson, Graham . 545Linart, Jean-Philippe .Liukkonen, SimoLiveri, Vincenzo TurcoLong, V.D. .Lorimer, J. Phillip .Lough, Roger M.Low, Hamish C. . .Lutfullah . . .Lyle, Samuel J. . .McAdam, Michael E. .McAlpine, Eoghan .Macca, Carlo .McCain, Colin C. .McCallum, Colin .McCanny, J.McCracken, David R. :McDonald, Malcolm P.McDowall, Joseph M. .McEwan, Iain J.McNicol, Brian D. .Madsen, H. E. LundagerMajer, J. R.March, Raymond E. :Marsden, Christine E. .Marshall, Roger M. .Martinus, Nicholas .Marx, Gunter .Mascherini, Renzo .Masood, A. K. M. .Mateo, Salvador .Mather, Roger E. .Matsumoto, Yoshio .Matthews, Colin J. .Matthews, G. Peter .Matthews, J. Ioan .Mattingley, B. I.Meares, P.Menendez, VicenteMeriaudeau, Paul .Mestdagh, M. M. .Mi&;, 0.I. . .Miguel, M. Da G. .Mineyeva, L. V. .Mingins, James .Mita, Kazuei .Mohazzabi, Pirooz .Moller, Bernard W. .Monk, Derek F. .Moore, Peter .Morrison, J. A. .Morterra, Claudio .Mortier, Wilfried J. .Moseley, P. G. N. .Muller, Heinz-D.Mulcahy, Joseph K. .Mullik, S. U. .Munnoch, Peter J. .Muttik, G. G. .Napper, Donald H. .Nazer, A. F. M. . .Nicholas, John E.Nicholson, DavidNicol, S. K.Nierzwicki, WitoldNigam, Santosh . .Ninham, Barry W. .Nip, Wing S. . .PAGE . . 2793 . . 2537,2836 . . . 436 . . . 2404 . . . 26611124 : 1360, 1707 . . 495 . . 1241. . 755 . . 2091 . . 1972 . . 334 . . 323. 509 . . 1464. 2274654 : 526, 1675. 2735. 1078. 1697. 545. 292385 : 654, 2505. 1419. 896.20 . . 112. 545 . 3891652238, 645, 2917. 1403 . 1355 . 1105 . 422. 1, 1499. . 154 . . 285 . 1631345' 2685, 2694564, 1033, 1627. . 290. . 2512 . 1584 . 826 . 1051. 2722 . 1877. 1132 . . 27031896 : 368, 2218. 1981 . . 1345. 2425 . . 910 . 1058. 29 . 2638 . 2552. 2324 . 2526 . . 22116 AUTHOR INDEX-PAOBNitta, Masahiro . . . . 2893Nome?Faruk . . . . . 296Nordine, Paul C. . . . 1526Noszticzius, Zoltan . . . 2537, 2836Nowatari, Hiroyoshi . . . . 2785Nozoye, Hisakazu . . . . 389Ng, Soon . . . . . . 1101Oakes, John . . 216,228, 1324, 2681Occhiucci, G. . . . . . 1848$herby, Ole . . . . . 513Ofenberg, H. . . . . . 143Ogawa, Kiyoshi - . . . 2893Okamoto, Byron Y. . . 2492Okubo, Tsuneo . . . 504, 1033, 1627Olteanu, M.. . . . 1670Onishi, Takaharu . . . 389, 833Ono, Yoshio . . . 2150O'Shaughnessy, Denis A. . . . 2661Pacia, Nicola . . . . . 1919Paniccia, Franco . . . . . 1512Paoletti, Piero . . 896Parboo, Dayaram'M. : . . 1856, 2645Parfitt, Roger L. . . . 1082Parkes, David A. . . . 1935, 1952Parrott, Trevor K. . . . 1456,2404Parsonage, Neville G. . . . 942, 1759Passiniemi, Pentti . . . 2537, 2836Paterson, Russell . . . 323,495Paul, Donald M. . . 1935Paul, Sylvia 0. . . . : 1546, 2829Pedley, Michael . . . . 359Peel, William E. . . 2274Pendleton, P. . . . . . 1114PCrez, Juan M. . . . . . 422PCter, Anna . . . 1201Pethica, Brian A. . 2685, 2694Pethig, Ronald . . . . 2355Pethrick, R. A. . . . 20Pethybridge, Alan'D. : . . . 64,73Phillipson, Nigel A.. . 257Pilling, M. J. . . 257Pitts, E. . . 1519Poltoratskii, Guinadi M: . 2007Posener, Marion L. . . 2231Possagno, E. . . . . 1848Povey, Andrew F. . . . 687Powl, John C. . 619Pratt, Graham . : 1589, 1733, 2477, 2769Pross, Addy . . . . . 755PuEar, Zvonimir . . . . . 987Pulham, Richard J. . . , . 431Purnell, Howard . . 85Quaegebeur, J. P. . . . . 143Quig, Alexander . . . 771Quinn, Colin P. . . . 706, 1935, 1952Quitan, Michael F. . . . 2289, 2605Radak, Vukosava M. . . 1150Rajbenbach, L. A. . . 941,1903, 2462Rao, C. N. R. . . I288Rastas, Jussi . . 2537, 2836Redpath, J. L. . 51Rees, Lovat V. C. 77i, 1809, 181'8, 1827, 1840Reid, David S. . . . . . 359Reid, Donald J. . . . . , 2139Reid, Euan .2829VOLUME 72, 1976Rendall, Henry M. . . . . 481Rengasamy, P. . . 376Riassian, M. . . . 925Richards, Edwin . . 942, 1759Richards, E. L. . . 1051Robb, Ian D. . . 1489Robb, J. C. . 1697Roberts, M. Wyn 540Rochester, Colin H. 876, 1584, 2498, 2753, 2930Rogers, David . . 1589, 2769Ronfard-Haret, J. C. . . I 143Rosenberg, Jerome L. . 448Rosner, Daniel E. : 842, S58, 1526Roy, Rabindra N. . . 2197Ruckenstein, E. . 764Rudham, Robert . : 1642, 1685Rudzinski, W. . . 453Russell, James D. . 1082Ruthven, Douglas M. . . 1043Sacchetto, Giuseppe A. . 1972Salai, Josip J. . . 1150Saleem, Syed M. . 1609Salim, Mohammed S. . . 1642Samman,N. . . . . 1495Saumagne, Pierre . . 1329Scheludko, A. . 281 5Scott, R. P. . 184, 197Scott, W.James . 1192Scurrell, Michael S. . : 8i8, 2512Searcy, Alan W. . . . . 290, 1889Seeley, M.-A. . . . 307Seibold: E. A. . . 273Sellers, Robin M. 1 799, 1464Sermon, Paul A. . . 730, 745Serrano, Maria T. . . 1534, 2265Shanson, Vivien H. . 2348.Sherwood, John N. . 1 2398, 2872Sherwood, Peter M. A. . 687Shimura, Michiko . . 2248Short, Richard T. . 2735Shukla, A. K. . . . 1288Sidebottom, Eric W. : . 2709Sime, Stuart J. . . 1144,2470Sime, Wendy J. . . 2470Sinclair, Roy S. . . 2091Singh, Surjit . . . . . 1694Sinha, V. K. . . . 134Slater, Richard M. : . 2416Smerkolj, R. . . . . 1188Smidt, Ruth E. . . 568Smith, Barry Trevor . . . . 355Smith, David Bradley . . 1241Smith, Edward A. 2876Smith, E. Brian 238, 6&5, 2917Smith, George D.'W. : . 1231Smith, Royston . . . 1489Smitham, James B. . . 2425Spiers, David J. . . 64, 73Spiro, Michael . 14iOY14i9, 1425,1477,1485Spitzer, Jan J. . . . . . 2108Sproule, R. C. . . . . . 509Srivastava, R. C. . . . 2631Staschewski, Dieter . . . . 2203Stone, Frank S. . . 2364Stone, W. E. E. . . 154Storey, Peter D. . . . . 85Straughan, Brian P. . . . 93PAGESchoonheydt, Robert A. . : 1;2,122AUTHOR INDEX-VOLUME 72, 1976 17Stroud, Henry J. F. .Sutton, marry C.Swallow, A. John .Swanson, A. .Swart, Edward K. .Swinton, F. L.Symons, hbrtyn C. R. *Szpakowska, hlaria .Takayanagi, Hiroshi .Tam, Nguyen The .Tamaru, Kenzi . .Tanaka, Kazuko .Taylor, DuncanTaylor, John A. G. :Taylor, John Watson .Taylor, Joseph F..Tchir, Morris F. .Tedder, John M.Tench, Anthony J. .Tepli, J. . .Terry, G. C. .Thomas, C. M. S. R. .Thomas, J. Kerry .Thompson, John F. .Thomson, Samuel J. .Thornton, Edward W. .Thunder, Anne E.Tiddy, Gordon J. T. .Tielen, Mia .Tiezzi, Enzo .Todd, John F. J.Toshev, B. V.Totterdell, Peter ni.Townsend, Rodney P. .Toussaint, Philippe .Trasatti, Sergio .Tregold, R. H. .Treiner, Claude .T r i m , David L.Triolo, Roberts .Tripathi, Jai B. P. .Trotman-Dickenson, A. F.Truscott, T. George .Turner, Irvine D. M. .Tutsch, R. .Tyler, Brian J. . .Tyler, J. Kelvin . .Tzias, Pierre .Ungarish, MoshePAQE . . 942, 1759 . . 2441,2452 . . . 1391 . . 2638 . . . 39720409, 1792,2876 . . 2381, 254521 50 : 257'7, 2592, 2598 .. 389, 8331121 : 3j4, 1114. . 2685, 2694 . . . 723 . . . 91710961177, 1300, 1707. 1553 . . . 285. . 1519. 238 . 2610. 1088251 6. . 431 . . . 1747 . . . 2793 . . . 1505. 5452815 : 14?7,1485. 661,2650 . 2301. . 2076 . . 509. . . 2007 . . 925 . 79933 : 966, 1027, 1428. . 2091 . 2829 . . 1559 . . 1448 . . 1782. . 20071 u i o , ni7,2484. 400UrFutia, G. . . 637Uruska, Irmina . 2381, 2545Uytterhoeven, Jan B. i76,6;4,1221, 1877,2793Valensin, Gianni . . . 1505van Assche, JanB. . . 376Vander Donckt, Emile . : 2301,2312Van Hook, W. Alexander . 58 3Van Sinoy, Alain . . 2301,2312Van Vooren, ClaudeVelghe, Firmin .Veltman, IanVernon, Charles A.Viana, Cesar A. N.Vickerman, John C.Vidaud, Patrick .Vikingstad, EinarVincent, Colin A.Voice, Philip J..PAQE . . . . 2301 . . . . 172 . . . 1733, 2477 . . . . 397 . . . . 1541 . . . . 40 . . . . 1058 . . . 1441 . . . 654, 2505 . . . . 2661Wifi, M.- .Williams, Ian M.Williams, Peter M. .Willocks, Elma .Willson, Robin L.Wilson, Christopher J. .Wilson, David N.Wojciechowski, B. W. .Wolstenholme, John .Wood, Robert H.Woolf, L. A. .Wright, John D. .Waghorne, W. Earle . . . 1294Walker, F. Ann . . 1856Walker,RaymondW. : . . 1715Walsh, David J. . 534Walsh, Robin . 100, 1212, 2137, 2901, 2908Walton, A. . . . 344Walton, John C. . 1360,1707Wan, J. K. S. . 1799Wardman, Peter . 1377, 2231Warman, John M. . . . 1368Warner, F. P. . . . 1064Webb, Geoffrey . . 2516Weiss, George PI. .. . 1342Werblan, L. . 307West, Kenneth 8. . . 8, 558Westerman, A. Valerie . 2498, 2753Wetton, R. E. . . 1064Wheeler, Barbara 'A. 1 1747White, Lee R. . . . 2526, 2844White, Terry 2197Whytock, David A. llY7, 18i0, 2143, 2284 . . 1165Weber, Bernard . . . . . 1919Weeks, Jr., Thomas J. . . 575Wells, Jean M. . . loo, 1212Wells, Cecil F. . . 601,910. 803 . . 925. 25162324 : 1362, 1856, 2645 . . . 2930. . 453 . . 40. . 2492. 1267. 1981Yasumori, Iwao .Young Colin, L. .Yue, Beatrice Y. .Zador, ErikaZaleski, Thomas A.Zambonin, Pier GiorgioZecchina, Adriano .Zimmerman, Donald N.Zuman, Peter .. 2785 . 122. 2685. . 1368 . 228415121553,2364. 409. 119Journal of the Chemical Society,Faraday Transactions I1TSSN 0300-923Journal of the Chemical Society, Faraday Transactions IISUBJECT INDEX-VOLUME 72, 1976PACE11, 1 Kinetic Spectroscopy (see also 11, 5 )Kinetic Spectroscopy in the Far Vacuum Ultraviolet.Part 2: Fluorine Atom ResonanceSpectrometry and the Measurement of F 2P Atom Concentrations. (Bemand andClyne). Part 3: Oscillator Strengths for the 33, 4s and 5s 3S-2p4 3P2 Transitions inAtomic Oxygen. (Clyne and Piper) . . . . 191, 2178Laser Fluorescence Study of the Hg(3P0) +N2 System. (Phiilips) 2082Laser Photolysis Studies of the Triplet State of Xanthone and its Ketyl' Radical in Fluid,E-t4A2 Luminescence and 4A2-+2E, ,TI(;&,) Absorption Spectia of the Cr(en):'+ Ion.Nanosecond Laser Studies of Photophysical'Pr&sses in the Benzene + TetracyanobenzeneMolecular Complex.(Craig and Rodgers) . 1259Quantitative Chemically Induced Nuclear Polarization (CIDNP) Study of the' Kine'tics okthe Photolysis of Pivalophenone in Various Solutions. (Firth and McLauchlan) . 87Rate Measurements of Reactions of OH by Resonance Absorption. Part 5: RateConstants for OH+N02(+M)+HN03 (+M) over a Wide Range of Temperatureand Pressure. (Anastasi and Smith) 1459Structure of Contact Ion Pairs in the Ground and First'Excited States. 'Aromatic Closed:Shell Anions containing a Five-membered Ring. (Vos, Maclean and Velthorst) . 63Solution. (Garner and Wilkinson) . 1010(Flint and Matthews) . . . . . . . 579II,2 Photophysics (fluorescence, phosphoresence, luminescence, dispersion, dichroism, etc.)Collisional Quenching of Nz ( A 3.ZL; v = 0,l) by N Atoms, Ground State N, and a PyrexSurface. (Vidaud, Wayne, Yaron and von Engel) .. 1185Effect of Concentration on the Triplet Yield of Pyrene in Pokmethylmet'hacryiate. (Avis,Avis and Porter) 51 1Energy Transfer from Excifed NO, to Moledular Oxygen. (Giachardi, Harris A d Waynej 619Excimer Emission in the Thennoluminescence of Gamma-Irradiated Hydrocarbon Glasses :Some New Spectra. (Al-Jarrah, Brocklehurst, Evans) . 1921Formation of CF: Ions in Photoionization of Hexafluoroethane. 860Isotope Effects in the Quenching of Electronically Excited Atoms. Part 4: Quenching oi1(5,P+) by Hydrogen and Deuterium Halides, H,O and D20. (Donovan, Fotakis &Golde) . . . . . . . 2055Long Range Energy Transier by Dipoie-Dipole and Exchange Interactions in Rigid' Mediaand in Liquids.(Pilling and Rice) 792Luminescence of Benzoic Acid and Methyl Benzoa'te at i7K. '(Acuha, Ceballos'and Moler;) 1469Mechanism of Intermolecular Energy Transfer between Tris-(acetylacetonato) lanthanoidMechanism of Quenching of the Triplet States of Organic Compounds by Tris-(p:dike;onatojComplexes of Iron(III), Ruthenium(II1) and Aluminium(II1). (Wilkinson and Farmilo) 604Phase-shift Studies of Hg(3P0) Reactions. Part 5: Kinetics of Hg, Excimer Reactions in thePresence of Nitrogen. (Ong, Freeman, McEwan and Phillips) . . 183Photochemical Hydrogen Abstractions as Radiationless Transitions. Part '1 : Ketones,Aldehydes and Acids. Part 2 : Thioketones, Quinones, Aza-Aromatics, Olefins andAzobenzenes. (Formosinho) .. 1313, 1332Quenching of Infrared Chemiluminesence. Part 4: Rates of Energy Transfei fromCO(49 v< 12) to Diatomic Hydrides and Deuterides. Part 5 : Rates of Energy Transferfrom CO(49uG 18) to Polyatomic Molecules. (Braithwaite and Smith) . . 288, 299Quenching of Toluene Fluorescence by Oxygen. (Lewis and Ware) . . 1851Reactivity of the ( l ~ l g ) ~ and 'dg States of Oxygen Produced by Direct Lase; Excitation.(Evans and Tucker) . . . . 1661B31fO: - X12: Systems of 2712 and 291 Molecular Constanfs, Laser-excited Fluore-scence and Franck-Condon Factors. tYee) . 2113Temperature Dependence of the Deactivation of Triplet Aromatic Molecuies by' MetalIons. (Marshall, Philipson and Pilling) .. 830Triplet-Triplet Extinction Coefficients of Anthracene and 9-Bromoanthracene'Dete;minedby a Ground State Depletion Method. (Ledger and Salmon) . . 883(Si& and Danby)Complexes in Solution. (Neilson and Shepherd) . 557Photophysical Processes in Flourinated Aceiones. * (Mekalfe'and Phillips) . . 1574222 SUBJECT INDEX-VOLUME 72, 197611, 3 Quantum and General Theory (including va!ence theory, ab initio calculations, computerAb Initio Study of Some Phenomena Associated with Core Electron Ionization. (Adams)Antiferromagnetism in Transition Metal Complexes. Part 7 : Critique of the HeisenbergModel and a Re-examination of the System of Three Copper(I1) Ions in a Linear Array.Applications of a Simple Molecular Wavefunction. Part 11 : Extension of FSGO methodto open-shell treatments.(Pakiari and Linnett) .Applications of a Simple Molecular Wavefunction. Part 12 : Openlshell Floating SphericaiGaussian Orbital Calculations for some Atoms and Ions. Part 13: Open-shellCalculations for Hydrogen-bridge Structures. (Pakiari and Linnett) . 1281,Part 14: Potential Barriers in Some Small Related Molecules. (Pakiari, Semkow 2ndLinnet t)Applications of a Simple Molecular Wavefunction. P&t 15: Spectroscopic Constants ofSelected First-row Diatomic Hydride Molecules. (Semkow and Linnett)Applications of a Simple Molecular Wave function. Part 16: Bond Angles and OrbitalsA Useful Theorem in Simple Molecular Orbital Theory. (Dkon) 'Calculation of the Electronic Structure for the Manganate and Hypomanganati Ions b y theSelf Consistent Field &Scattered Wave Method.(Jasinski and Holt) . .'B-Chemical Shifts of Diboranes, Polyboranes, Carboranes and Coupling ConstantsIJ("B'H), IJ(lLB'lB). (Kroner and Wrackmeyer) .Derivation of Molecular Spectra from the Polarized Spectra of Monklinic Crystals andits Application to the Electronic Spectrum of Bis(meth0xyacetato)-diaquacopper(u).(Hitchman) .Electronic Structure of the Chlorine Pseudohalides 'ClNCO and CCNNN: (Kosmus,Emission of Electrons from Solutions.' (Brodsky 'and Tsareviky) .Enumeration of the Kekule Structures in Conjugated Hydrocarbons. (Randic) 'Exchange Interaction in Polynuclear Complexes. Part 1 : Principles, Model and 'Appli- .Exchange Interaction in Polynuclear Complexes.Part 2: Antiferromagnetic Coupling in Bi-Excitation Functions for the Reactions of Tritium Atoms with HF and DF. '(Mal&me-Geometrical Isomerism in Vinylmethylene. (Chung) .Graph Theory of Free Radicals. Validation of a Recent Assertion and its Reiation' to theGround Electronic State and Geometry of the CO, Radical Lion.' (So)Iterative Variation of Charge Dependent Atomic Orbital Expcnents in ApproximateMolecular All-valence Electron Linear Combination of Atomic Orbitals (L.C.A.O.)Methods. (Figeys, Geerlings and Van Alsenoy) .Modulated Perturbation Theory for Molecular Interactions: Par't 1 : An Exact Skcond-order Calculation for the Ground State of H:. (Magnasco, Battezzati and Figari) .Molecular Graphs having Identical Spectra. (Randic, TrinajstiC and ZivkoviC) .Monte Carlo and HNC Calculations for Molten Potassium Chloride.(Adams)Monte Carlo Trajectory Study of the Family of Reactions H+X,+HX+X (X= F, Ci, Br, I).(Pattengill, Polanyi and Schreiber) .Non-Empirical Valence-Electron Calculations on the Diatomii Halogens and Interhaiogens..(Hyde and Peel) . .Rational Function Approximation of the Configuiation'Interaction Optimized''C,+ GroundState of Hz and HeZt. (Leclerc) . . . .Reorientation of Water Molecules free from Hydiogen Bonding. iEvans)Second-Order MS-MA Calculation of the First Excited State of Ht by Modified Pei-turbation Theory. (Battezzati and Magnasco) . .Self-consistent Group Function Calculations of the Ethane Barrie;. (Musso, Vallini andMagnasco) .. .Spin Correlation in the Geminate Recombination of Radical Ions in Hydrocarbons.Part 1 : Theory of the Magnetic Field Effect. (Brocklehurst) .B311(O+) States of IF, ICl and IBr. Part 1 : Calculation of the RKR Turning Points andFranck-Condon Factors for the B-X Systems. Part 2: Observation and Analysis ofthe Excitation Spectra of IF and ICl. (Clyne and McDermid) . . 2242,Study of Hz and He;+ Using Three- and Four-Parameter Non-integral-n 1s Basis Functions.Theory of the F: Surface Centre'in MgO. isharma and Stoneham)Vibrational-Rotational Levels and Wavefunctions of Diatomic RKR Poten'tials. ' Vari-simulation, etc.)(Jotham, Kettle and Marks) . . . .of Singlet CH2. (Leok Peck Tan and Linnett) . . .Nachbaur and Faegri, Jr.) . . . .. .cation to the Binuclear Complexes of Chromium(m). (Kahn and Briat) .nuclear 0x0-bridged Iron(m) Complexes. (Kahn and Briat) .Lawes) . . . . . .Pairing Theorem. (Honeybourne) . . .(Leclerc) . . . *ational Approach. (Baraldi, Momicchioli and Bruni) . . . . . .PA0 B38312564 112881298150322332821304228354802178123226814418784563464671 5222441372897571755213850810211869225275991 388SUBJECT INDEX--VOLUME72,1976 2311, 4 Relaxation Phenomena (dielectric, magnetic, ultrasonic, etc.)Consideration of Dielectric Relaxation and the Kerr-Effect Relaxation in Relation to theReorientational Motions of Molecules. (Beevers, Crossley, Garrington and Williams)Coupled Relaxation in AX2 Spin Systems.Dependence of Effective Relaxation Times onMethod of Measurement and Application to Determining Internuclear Distances.Dielectric and Optical Studies of a Nemat'ogen i4, 4-n-Heptyl-cianob&henyl), (Davies,Dielectric Relaxation of Tri-n-butylammonium Picrate in Benzene Solutions. (Badiali,Cachet, Cyrot and Lestrade) .Dielectric Studies of Non-electrolyte Solukns. ' Par; 3 : ConfoAational Equilibria inlY2-Dichloroethane and Dimethyl Carbonate. (Thiebaut, Rivail and Greffe) . .Dynamic Viscosity of Dilute Polymer Solutions at High Frequencies of Alternating ShearElectro-optical Kerr Effect in Solutions of Benzylidene kniline and its Derivatives.Out of Plane Atomic Vibrations and Relaxation Mechanisms. Metal Chelates and0,('2'5) Relaxation in Collisions.Part 2 : Temperature Dependence of ;he Relaxaiion byHydrogen. (Braithwaite, Ogryzlo, Davidson and Schiff)Rotational Dynamics of CH3C1 and CH,CF, in the Fluid State. (Davies,'Evani and Evan;)Spin-lattice Relaxation Studies of Organophosphoris Compounds. (Harris and McVicker)The Kerr Constant of Water and other Pure Liquids at 633nm. (honey, Battaglia,Ferfoglia, Millar and Pierens) . . . . . .Ultrasonic and Viscoelastic Relaxation in Solutions of Poly(2,k-Dimethyl-p-phenyleneOxide). (Evman, North, Pethrick and Wandelt) . . .Vibrational Relaxation in OCS Mixtures. Part 1 : Measured Relaxahon Times for Pure OCSand for OCS in Mixtures with Helium-4. Helium-3, normal Deuterium, ortho-Deuterium,HD, normal Hydrogen and para-Hydrogen.(Simpson, Gait and Simmie) . .(Scrivens and Heatley) . . .Moutran, Price, Beevers and Williams) . . . . .Dielectric Relaxation in Eugenol. (Alper, Barlow and Kim)' . . .Stress. (Cooke and Matheson) . . . . . . . .(Beevers and Williams) . . . . .Disiloxanes. (Dasgupta) . . . .Theory of Non-linear Dielectric Effects in Liquids: (Malecki) . . . .11, 5 Spectroscopy (a) Microwave, infrared, RamanCentrifugal Distortion of Carbonyl Sulphide in Excited Vibrational States. (Smith) .Cryogenic Photolysis Studies. Part 2: Infrared Spectrum of Nitrosomethane Monomer.Effect of Pressure and Temperature on the Intermolecuiar Mean Square 'Torque in LiquidCS2 and CCL. (Evans and Davies) . . . . .Hydrogen Bonding in the Gas Phase. Part 3 : ' Infrakd S'pectroscopic Investigation ofComplexes formed by Phenol and by 2,2,2-Trifluoroethanol.(Hussein, Millen andMmes) . . . . . . . . . . .Part 4: Infrared Spectroscopic Investigation of O-H.-O and C-H-N Complexes :Alcohol+ Ether and Trichloromethane-t Amine Systems. (Hussein and Millen) .Infrared and Far Infrared Spectroscopic Studies of the Adsorption of Water Molecules onInfrared, Raman and Force Field Studies of Methyl- and Perdeuteriomethil-niercury(n)lnfrared Spectra and Hydrogen Bonding of Monoalkali Salis of Malonic Acid and the&Infrared Spectra of Matrix-isolated Species; Reaciion Produck of MgFz'with Group I andInfrared Study and Thermodynamics of Hydrogen Bonding in Dietiylene Glycol MonoalkylEthers. (Prabhumirashi and Jose) . . . .Microwave Spectrum and Non-Planarity of 2-Amhopyrimidine. (Lister, Lowe andPalmieri) .. . . . . .Model Interpretation of the Far 'Infraied Absorptions k Compressed Gaseous and LiquidBromotrifluoromethane, CBrF,. (Davies and Evans) . . .Models of the Orientational Autocorrelation Function from Far Infrared Absorption &Liquid and Rotator Phases. (Evans) .Molecular Electrostatics. Part 2: Experimentai Techniquk of 'Electhc Field InducedInfrared Absorption Spectroscopy of Liquids. Part 3 : Liquid-Phase Electric FieldInduced Infrared Absorption in Tetrachloroethylene, Tetrabromoethylene, Diphenyl-acetylene and But-2-yne. Part 4 : Determination of Disordered-Multipole InternalElectric Fields in Liquids from the Infrared Intensity of Formally Forbidden Bands:Studies on Diphenylacetylene and Tetrachloroethylene. (Jones) .. 1397, 1406,Pure Rotational &Raman Spectra of I6O2, 160180 and I8O2. (Edwards, Good andLong . . . . . . . . . . . . . .(Barnes, Hallam, Waring and Armstrong) .High-Area Alkali Halide Surfaces. (Smart and Sheppard) . * .Halides. (Goggin, Kemeny and Mink) .Dialkyl Derivatives. (Belhekar and Jose) . .Group II Fluorides. (Kana'an, Hauge and Margrave) .PAGR148221 641447934123120246792171171620751901229 17241 04195741 722981120668669370710252191199117219204072714218624 SUBJECT INDEX-VOLUME 72, 1976Pure Rotational Raman Spectra of the Chlorine Species, 35C12 and 35C137C1. (Edwards,Pure Rotational Raman Spectrum of Fluorine.(Edwaids, Good and Long) .Raman Spectroscopic Study of Semicarbazide Hydrochlorise above and below the Ferro-Rayleigh Scattering. Depolarisation Ratios of Cyclohexane, Caibon Tetrachloride andResonance Raman Spectrum of the Tetrabromof&rate(m) Ion. (Clarke’ and Turt lei *.Rotational Brownian Motion in Liquid and Plastic Crystalline CBr4 from Far InfraredSimplified Treatment of S tepanov’s Vibrational Predissociation Effect in HydrogembondedSolvation Spectra. Part 50: Spectrophotornetric Studies of the Solvation of Nitrate Ions inSpectroscopy at Very High Pressures. Part 8: An Infrared Study of Shear-Stress-LducedTransitions in Ammonium and Sodium Nitrates. (Adams and Sharma) . .“Symmetrical” and Asymmetrical (NH ... N)+ Hydrogen Bonds.Infrared Investigations.(Brzezinski and Zundel)Use of Generalized Langevin Thkory tb Des’cribe Far Infrared Absorptions in ”on-dipolarLiquids. (Davies and Evans)Vapour Phase Raman Spectra of the Moiecules MH4(M C,Si,Ge ‘or Sn) and MF4(M = C,Si or Fe). Raman Band Intensities, Bond Polarisability Derivatives andBond Anisotropies. (Armstrong and Clark) . . . . .Vibrational Band Shape and Intensity Studies on Molecular Motions and Interactions inCondensed Phases. Part 3: Effects of Complexation on the Molecular Dynamics ofPyridine. (Yarwood) .Vibrational Spectra and Molecular Confoimation of ‘Propargyl Ethyl’ Ethe;. (Charles,Cullen and Owen) .Vibrational Spectroscopy at Very High Pressu;es. Part 6: Infiared ‘Spectra of‘ SilverNitrate Polymorphs.(Adams and Sharma). Part 7: 1.r. Spectra of Potassium Nitrate.(Adams and Sharma) . . . . . 848,GoodandLong) . . . . . . . . .electric Phase Transition. (Fawcett and Long)Benzene. (Pierens) . . .Induced Absorptions. (Davies, Evans and Evans) .Species. (Robertson) . . . . . . . .Protic and Aprotic Media. (Findlay and Symons) . .(b) electronic (visible, absorption and emission)Absorption Spectra of Doped Anthracene Crystals. Determination of the Direction ofElectron Energy Loss Spectrum of Nitrous Oxide. (Dance and WalkerjElectronic Structure of Some Simple Third-row Hydrides and Flourides. (Findlay)’ 1Intensities of Vibronic Origins in the Electronic Spectra of Amino and Aquo CoordinationIonisation of Hydrog5n Sulphide, Seienide‘ and *Tellu;ide by Electron’ Impact.(Balkis,Ion-Pair Formation of the Carbanions of Xanthene and Thioxanthene Studied by theirAbsorption and Fluorescence Spectra. (Vos, Rietveld, MacLean and Velthorst) .Low Energy Electron Impact Spectra of some Simple Alkynes. (Stradling, Baldwin,Magnetic Circular Dichroism Studies of the Interaction of Molecular Iodine with OrganicNear Ultraviolet Optical Activity of Chiral Pyridine Derivatives (Chin-Yah Yeh andRole of Hyperfine Structure in Atomic Absorption. ’ Osciilator ‘Strengths in Br ‘and I.Rotational Analysis of the 2A’+iA” Emission Band Systkm of‘H02 i t 1.43 pm. (Freedmanand Jones) .Spectroscopic Studies on Single Crystals haiing the Fluorite Lattide. Part 1 :‘The Funda-mental Absorption Edge; Urbach’s Rule and the Debye Temperature in CeO,.(Griffiths, Davies and Hubbard) .. .Study of Elementary Reactions by Atomic’ Resdnance Absorption with a Non-re’versedSource. Part 1 : The Reaction of C1 +O3-tC1O+O2. (Clyne and Nip) .Translational Energy Release in the Loss of Fluorine Atoms from the Ions SFZ , CF:, andC2FZ. (Simm, Danby, Eland and Mansell) . . . . . .Use of the Memory Function to Simulate the Debye and Poley Absorptions in Liquids.(Evans and Evans) . . . . . . .the Transition Moment of the Dopant. (Bridge and Gianneschi)Complexes. (Flint) .Gaines, Ozgen, Ozgen and Flowers) .Loudon and Maccoll). . . . . . . . .. .Solvents. (El-Kourashy and Grinter) .Richardson) . .(Tellinghuisen and Clyne) . .9279843132108188521471153820206921 271194119673511344162221053887215241636871186033 178 32077658384261169(c) photoelectronAnalysis of the X-Ray Photoelectron Spectra of Transition Metal Compounds usingApproximate Molecular Orbital Theories.(Sherwood) . . . 179SUBJECT INDEX-VOLUME 72, 1976 25PAGEBonding Studies of Compounds of Boron and Elements of Groups 3-5. Part 16: Ab InitioSCFMO Calculation and He(1) Photoelectron Spectra of Halogen-bridged DimericGroup 3 Metal Halides and Methylmetal Halides. (Lappert, Pedley, Sharp andCharacterization of Surface State Strkture'on the (lli) Fa& of a Clean Copper 'SingleCrystal using Mercury Adsorption and Angular-resolved Photoelectron Spectroscopy.(Lloyd, Quim and Richardson) .. . 1036Exchange Splitting of the Chromium 3s Signals. in the X-iay Photoeiectron Spectra df&CI-(CN)~ and &Cr(NCS)6. (Orchard, Stocco and Thornton) , 1045He(1) Photoelectron Spectrum of the P2(X1Zg) Molecule. (Bulgin, Dyke and Morris) . 2225He(I) Photoelectron Studies of C-Nitroso-compounds. (Egdell, Green, Rao, Gowenlock andPfab) . . . . 988He(1I) Photoelectron'Specira of Diatomic Aikali Halides. (Potts and Williams) . . 1892High Resolution Photoelectron Spectrum of Hydrazoic Acid. (CvitaS and Klasinc) 1 240Photoelectron Spectra of Phenazine N-Oxide and some of its Derivatives. (Albini and Markj 463Photoelectron Spectrum of Nitrosyl Chloride. (Abbas, Dyke and Morris) . . . 814Photelectron Spectrum of Sulphur Trioxide.(Alderdice and Dixon) 372Ultraviolet Photoelectron Spectra of Thiazyl Chloride. (DeKock, Shehfeh; Lloyd andRoberts) 807Vacuum Ultraviolet Photoelectron Spectroscopy df Transient' Species. Part 61 A St'udy okVibrationally Excited Hydrogen and Nitrogen. (Dyke, Jonathan, Morris and Sears).Part 7: The Methyl Radical. (Dyke, Jonathan, Lee and Morris) . . 597, 1385Valence Orbital Photoelectron Spectroscopic Studies of Free Molecules with Zirconium MX-Ray Photoelectron Spectroscopic Studies of Some Iodine Compounds. (Sherwodd) . 1805Guest) . . . . 539Soft-X-Ray Excitation. (Allison and Cavell) . . . 118(d> electron spin resonanceAnisotropic Rotational Diffusion. An e.s.r. Investigation of the Anisotropic InteractionDetermination of the Acidity Constants or somi Phenol * Radical Cations by means ofElectron Paramagnetic Resonance Investigation of Oxygen Photoadsorption &d itsReactivity with Carbon Monoxide on Titanium Dioxide : the 0:- Species.(Meriaudeauand Vedrine) . 472Electron Spin Resonance of the Mn2+ Ion in the Study of the' Mobility of Water Adsorbedon Silica Gel and ?-Alumina. (Burlamacchi, Martini and Ottaviani) . . . 324Electron Spin Resonance Studies of Cation Radicals of Some Alkylphosphines. (Iwaizumi,Kishi, Isobe and Watari) . 113Electron Spin Resonance Study of Certain Met'allised Dyes absorbed into 'Wooi. (DkElectron Spin Resonance Study of Solute-Solute Interactions in Aqueous Solutions con-taining Transition Metal Ion Chelates of 4,4',4",4"'-Tetrasulphophthalocyanine.(DeBolfo, Smith, Boas and Pilbrow) . . . 481Electron Spin Resonance Study of the Reactions 0; Hydrogen' Atoms in Aqueous SulphuricAcid Glasses. Part 2: Reaction with Amino-acids. Part 3: Reaction with Bio-chemicals containing Sulphur. Part 4: Reaction with Simple Peptides. (Falle, Daintonandsalmon) . . 2001, 2014,2019201Hg Quadrupole Tnteraciion in the Electron Spin Resonance of the CH2HgC1 Radical.(Kerr, Wargon and Williams) . . . . . 552Kinetic Effects in the Electron Spin Reson'ance Spectra of some Semiquinones. iDixonMossbauer Studies of Electron Spin Relaxation and Radioiytic Effects' in Diluted Tris-Orientational Order of a Spin Probe Dissolved in Nematic Liquid' Crystals. An EiectronQuadrupole Relaxation and Asymmetric Linewidth Effects' in the E.S.R.Spectra of aBromoacyl Nitroxide. (Hudson and Treweek) . . a55Radiation Mechanisms. Part 10: Comparison between the Effects 'of Fast NeutronIrradiation and W o y-Irradiation of a Range of Ionic and Non-ionic Materials.(Mishra and Symons) . . . 747Temperaturedependent Hypekne Coupling Cbnstants in Eledtron 'Spin Resonance.Part 4: Out-of-Plane Vibrations of the Ring Protons in the Cation of p-Phenylenedia-mine. (Bullockand Howard) . . . . . . . . 4 6 9Tensor. (Luckhurst and Setaka) . . . 1340Electron Spin Resonance. (Dixon and Murphy) . 1221Bolfo, Smith, Boas and Pilbrow) . . . . . 495and Murphy) . . . 135(acetylacetonato) irc?n(ru). (Bancroft and Sham) . . 1706Resonance Investigation. (Luckhurst and Yeates) .996(e) nuclear magnetic resonance, quadruple resonanceConformation and Reorientation of Acetophenone in Solution. A Proton and DeuteriumMagnetic Resonance Study in a Nematic Solvent. (Emsley, Lindon, Street and Hawkes) 13626 SUBJECT INDBX-VOLUME 72, 1976Investigation of the Hydrogen Bonding in Chlorocarboxylate Anions using 35Cl QuadrupoleResonance Spectroscopy. (Lynch, Waddington, O'Shea and Smith) .Isotropic Proton HyperEne Coupling Constants of Two Cationic Nitroxides. (Fox) .Molecular Motion in Solid n-77 Molecular Complexes. Part 3: Pulse N.m.r. Measurementson Solid Charge-Transfer Complexes of Naphthalene and Pyrene. (Fyfe, Harold-Smithand Ripmeester) .Nitrogen Nuclear Magnetic Resonance' Spectroscopy. Part 6 I Corrklation of "N ChemicalShifts and Nuclear Quadrupole Coupling Constants in Nitroso (Nitrosyl) Compounds.(Mason) .Nuclear Magnetic R&ona& Gvestigation 'of PykdineL4-aldehyde' Oriented in a NematicLiquid Crystal-Internal Rotation and a Molecular Reorientation.(Orrell and Slk)Nuclear Quadrupole Resonance of Charge Transfer Complexes. Part 3: A I4N and 35Cln.q.r. Study of the 1 : 1 Complex of 3,5-Dichloropyridine with Iodine Monochloride.Ongm of Isotropic Shifts in Lanthanide Complexes: A Study of the Temperature Depen-dence of the H n . m .r. Spectra of the Te t rakis-N,N-die th y ldi t hiocarbama t olant hana t e(m)Anions. (Hill, Williams and Zarb-Adami) .Studies of lg9Hg Nuclear Shielding Anisotropies and their Relation to Isotropic ChemicalShifts. (Kennedy and McFarlane)Structure of Tetraethylammonium tetrakis-k,N-diethyidithiocarbamatolanthanate(& IonPairs in Solutions.(Hill, Roberts, Williams and Zarb-Adami) . . . .Structures of 1,3,5-Trichloro- and 1,3,5-Trichlorotrifluoro-benzene Derived from n.m.r.Spectra of Nematic Solutions. (Emsley and Lindon) .Temperature Independent Contribution to the Paramagnetic Susceptibility of Copper(;)(Bowmaker) . .Acetate. (Hill) . . .cf) neutron scatteringInelastic Neutron Scattering by Water in an Ordered Tobacco MGsaic Virus Solution.Inelastic Neutron Scattering from the Alkali 'Metai Borohydrides and Calcium Borohydride.Inelastic Neutron Scattering from Zirconium Borohydride. (To&inson' and Waddington)Interactions between &-Ethylene Ligands studied by Inelastic Neutron Scattering.Internal Torsional Modes in Methyl Haiogenocarbons Studies' by Inelasiic NeutrohInternal Torsional Modes in Mixed Methyl Halogeno-compounds.of Group IV ElkmenisLibrational and Torsional Modes in Hydrazinium, N2H$+, Salts Studied by Inelastic NeutronMolecular Rotations in the Plastic Phases of C6FgH3 and Ck F12. (Leadbetter, Tbrnbuiland Smith)Structure and Dynamics of Microcrystalline Graphite, Graphon, by Neutron Scattering.(Gamlen and White) .Torsional and Librational Modes of the Monomet'hylankonium ion, CH3NH:, in it's Salts,Studied by Inelastic Neutron Scattering. (Ludmanm, Ratcliffe and Waddington) .Torsional Modes in Multimethylammonium Halides. Studies by Inelastic NeutronScattering. (Ratcliffe and Waddington) .. .(Hecht and White) .(Tomkinson and Waddington) .(Howard, Waddington and Wright)Scattering. (Ratcliffe and Waddington) .Studied by Inelastic Neutron Scattering. (Ratcliffe and Waddington) .Scattering. (Ludman, Ratcliffe and Waddington) . .Neutron Diffraction Studies on Collagen. {Whitk, Miiler and Ibei) .. . .PAOE1980975226920649411964149416531267143663 14395281245513182118401741220543544617591935(g) ion cyclotron resonance, mass spectrometry etc.Comparative Chargeexchange Mass Spectrometric and Argon-sensitized RadiolyticProduction of Gas-Phase Radical Anions by Reaction of 0-- Ions k t h Organic Substrates.Studies on Methanol. (Jonsson and Lind) . . 906(Dawson and Jennings) .. 700II, 6 Statistical MechanicsAdsorption of Fluids. Improved Calculation of the Density Profile. (Navascues) . 2035Colloidal Dispersions. A Study of their Order using the Percus-Yevick Equation.Conformational Properties of a Polymer 'Con&ed between Two Adsorbing S&faces.(Chan, Davies and Richmond) 1584Continuous Charge Distribution Models of Ions in Poiar Media. ' Part' 3: The Effects ofTetragonal and Octahedral Distortion. Part 4: Planar Elliptic Ring Systems.(Schmidt) . 1048,1061Derivation and Interpretation of the Spectra of Aggregates. ' Part'4: Adiabatic Theory ofExciton Interactions in Dimers. (Gianneschi and Kurucsev) . . . 2095(Keavey and Richmond) . . 77SUBJECT INDEX-VOLUME 72, 1976Double Layer Interaction of Two Charged Colloidal Spherical Particles of a ConcentratedDispersion in a Medium of Low Dielectric Constant.Part 4: Conducting Particles inEffect of Damping Mechanisms on Electron Transfer Reactions. (Schmidt) . . .Electrostatic Models in the Theory of Solutions. Kharkats, Kornyshev and VorotyntsevEnergy of Interaction between a Monolayer and a Dielectric Adsorbent. (Duniec andGeiation in Concenirated' Critkally 'Brandhed Polymer Solutiork. Percolzhon &lingHard-Sphere Fluid Equation of State. (Woodcock)Molecular Electrostatics. Part 1 : Theory of Disordered-Multiple 'Inteial Electric 'Fieldsin Fluids. (Jones)Molecular-statistical Calcuiation' of the Thermodynamic Characteiistics 'of Adsorpfion ofSaturated and Unsaturated Hydrocarbons on Graphitized Thermal Carbon Black.Origin Invariance of the Fully Retardeh Rofational Strength.(King)Potential Energy Curves and Bronsted Exponents in Proton-transfer Reactions. (hell) :Quantum Collective Model of Ionic Solvation. (Schmidt)Quantum Collective Treatment of Inner Sphere Reactions. Part 1.' Part 2: ContributionsReaction Kinetics of Polymer Substitutents : Neighbouring-&oup Effect's for 'Ideal Mole-Reduction of Certain Matrix Expressions in the Statistical Theory of Chain MoleculeRole of Collective Behaviour in Polyatomic Molecules. a (Schmidt)Study of Physical Adsorption using the Mean Spherical Model. (Mitchell and Richmond)Theory of Self-Assembly of Hydrocarbon Amphiphiles into Micelles and Bilayers.Three-dimensional Lattice Model for the WaterlIce System.* (Bell' and Salt) . .Wien Dissociation in Very Low Intensity Electric Fields. .Contact. (Feat and Levine) . . . . . . .Ninham) .Theory of Intramolecular Bond Cycles. (Stauffer) . . . .(Kiselev and Poshkus) . . . . .from the Ionic Solvation Surface. (Schmidt) . . 1125,cules with Unique Ends and Related Model Schemes. (Boucher) . .Configurations. (Madsen) .(Israelachvilli, Mitchell and Ninham) . . .(McIlroy and Mason)XI, 7 Thermodynamics (reversible and irreversible)Adsorption Potential of Hz and N2 on 100 Plane of a NaCl Distorted Lattice. (EphrairnandFolman) . . . . . . . .Application of the Flory-Huggins Theory to Nematic&tropic Phase Equilibria.(Kronberg and Patterson) .Calculated Molecular Orientational Disorder in Lthra'cene Crystals. (Craig; Ogilke andChemical Effects of 'Nuclear Tkmsformati'ons in the Alkaii Metal Chlorides.Part 4:Effect of Solute Size and Shape on Orientational Order in Liquid Crys'tal $stems.Equations for the Repulsion Component of the LattiA Energy as' Deribed from a'DirectMinimsation of the Total Lattice Energy. (Jenkins) . . . .n-Fluid Models and Phase Equilibrium. (Hicks) .Generalized Treatment of Alkanes. Part 5 : Branching and Buttressing Effects:(Somayajulu and Zwolinski) . . .Glass Transition in the Hard-Sphere Model.' (Woodcock) : :Interpretation of Rotational Disorder in Crystalline Paraterphenyl in terms of Non-bondedInteractions. (Ramdas and Thomas) . . .Intersystem Crossing and Internal Conversion in Benzene Vapour at Low Pressures.(Forrnosinho and da Silva) .. . . .Investigation of Tautomeric A-H-a-B + A-...H-B+ Equilibrium by Linear and Non-linearIonization Potentials, Electron Affinities and Screening Constants. Part - 8 : FurtherDevelopments. (Baughan) . . . .Low Temperature Crystalline Phase Transition in Some Eipasolite-Hexachlbrides.(Schwartz, Watkins, O'Connor and Carlin)Model Fluid Mixture which Exhibits Tricritical Points. Part 1. ' (Guerrero, Rowlinsonand Morrison) .Molecular Motion and Oiientat'ional 'OrdeE in a' Nematic Liquid Crystal. An EiectronResonance Investigation. (Brooks, Luckhurst, Pedulli and Roberts) .Perturbation Expansion for Onsager's Linear Law for Wien Dissociation of a . WeakElectrolyte. (Mason and McIlroy) .Prediction of Ordered and Disordered States in Colloihal Dispersions.* (Snook and VanMegen) . .Rate of Homogeneous Electron Transfer Reactions in Polar Soivents' in the AbnormalRegion. (Schmickler) . . . * . . .Reynolds) . .Doped Alkali Chloride Matrices. (Maddock, Suh, Kasrai and Raie)(eonberg, Gilson and Patterson)Dielectric Polarization. (Malecki) .. .27PAGE50117363611513135473 13989502252088109911441697827107416131525765906711686160325716731569423221 316671251204412141275565197065 121952163028 SUBJECT INDEX-VOLUME 72, 1976PAGEStudy of Extended Defects in Molecular Crystals by the Atom-Atom Potential Method.Transverse Observations of Williams Patterns in the Nematic Liquid Crystal MBBA:Part 1 : Slip Planes in the Anthracene Crystal.(Mirsky and Cohen) . 2155(Watanabe and Jennings) . . . . . . . . . 173011,8 Transport Phenomena (see also I, 6)Continuous Charge Distribution Models of Ions in Polar Media. Part 1. (Schmidt andMcKinley). Part 2: Self and Interaction Energies for Soft Charged Ring SystemsDissolved in a Polar Medium. (Schmidt) . 143, 171Effect of Purification on Frequency Dependence of the Electrical Properties of CopperLarge Scale Intramolecular Motion in Polymers. (King and’Treadaway) : : . 1473Permeation Time Lag Analysis of “Anomalous” Diffusion. Part 1 : Some Considerationson Experimental Method. (Roussis and Petropoulos) . . 737Photoconductivity of TCNQ Single Crystals in the Presence of Electron Donor Gases.(Alderdice and Calvin) .. . . 1916Switching in Poly(N-vinylcarbazole) Thin Fi’lrns. * (Sadaoka and Sakai) . . 1911Phthalocyanine Discs. (Sadaoka and Sakai) . . 37AUTHOR INDEX-VOLUME 72,1976PAGE PAGEAbbas, Muniem1. . . . . 814 Craig,D.P. . . . . . 1603Acuiia, A. U. . . . . . 1469 Crossley, J. . . . . 1482Adams, David B. . . . . 383 Cullen, Frances C: . . . . 351Adams,D. J. . . . 1372 Cvitas, Tomislav . . . . . 1240Adams, David M. . . 848, 1344, 2069 Cyrot, Alain . . . . . 1231Albini, Angelo . . 463Alderdice, David S. . . 372, 1916 Dainton, Sir Frederick S. . 2001, 2014, 2019Al-Jarrah, Mustafa . . . . 1921 Danby, C. J. , . . . 426, 860Allison, David A. . . . . 118 Dance, Donald F. . . . .2105Alper, Turhan . . . . 934 Dasgupta, Sunil . . . . 1716Anastasi, Christopher . . . . 1459 da Silva, Abilio M. . . . . 2044Armstrong, J. Ronald . . . . 1 Davidson, J. A. . . 2075Armstrong, Robert S . . . 11 Davies, Brian 1584Aroney, Manuel J. . . 724 Davies, Graham J: 46, 1194, 1206, 1901,2147Avis, E. . . . . 511 Davies, Manse1 . . . . 1447Avis, P. . . . . 511 Davies, Mervyn J. . . . . 765Dawson, J. H. J. . . 700Badiali, Jean-Pierre . . . 1231 De Boifo, Joan A. . . : 481, 495Baldwin, Michael A. . . 871 DeKock, R. L. . . 807Balkis, T. . . 524 Dixon,R. N. . 372Banc;oft, G. Michael . . . 1706 Dixon, William T. . : i35,282,1221Baraldi, Ivan . . 887 Donovan, Robert J. . . . . 2055Barlow, A. John . . . 934 Duniec, JacekT. 1513Barnes, Austin J.. 1 Dyke, John M. . 547,8i4,1385,2225Battaglia, Maurice R. . . 724Battezzati, Michele . . 22, 508 Edwards, H. G. M. . . 865,927,984Baughan, E. C. . . . 1275 Egdell, Russell . . . . . 988Beevers, Martin S. . . 1447, 1482, 2171 Eland, J. H. D. . . . . . 426Belhekar, A. A. . . 2191 El-Kourashy, Abdel-Ghany . 1860Bell, G. M. . 76 Emsley, James W. . 1365, 1436Bell, Ronald P. . . . 2088 Ephraim,A.Ben . . . 671Bemand, Peter P. 191 Evans, Dennis F. . . 1661Boas, John F. : 481, 495 Evans, Gareth J. . . 1169, 19dl,2147Boucher, Ernest A. . 1697 Evans, Margaret . 1921Bowmaker, Graham A. 1964 Evans, Myron W. 40, 72j, 1169, 1194,Braithwaite, Martin . : 288, 299, 2075 1206, 1901, 2138, 2147Bridge, N. James . . . 1622Brocklehurst, Brian . . . 1869, 1921 Faegri, Jr., Knut .802Brooks, S. A. . . . 651 Farmilo, Alan . . . 604Bruni, Maria C. . . . . 887 Fawcett,V. . . . 313Brzezinski, Bogumil . . 2127 Fkat, G. R. . 501Bulgin, Denis K. . . 2225 Ferfoglia, Robert . . 724Burlamacchi, Leo . . . 324 Figeys, Hubert P. . . . 715Findlay, Robert H. . . . . 388Cachet, Hubert . . . . . 1231 Findlay, Tristan J. V. . 820Calvin, Melvin . . . . . 1916 Flint, ColinD. . . : 579, 721Carlin, Richard L. . . 565 Flowers, M. C. . . . . . 524Cavell, Ronald G. . . . . 118 Folman, M. 671Ceballos, A. . . . . 1469 Formosinho, Sebastigo J. : 131'3, 13j2,2044Chan, Derek . . . . 1584 Fotakis, Constantine . . . . 2055Charles, Stuart W: . . . 351 Fox,KatherineK. . . . . 975Chin-Yah Yeh . . . . 331 Freeman, Colin G.. . . . 183Chung, C. S. . . . 456 Freedman, Philip A. . . . . 207Clark, Robin J. H. . 11, 1885 Frith, P. G. . . . . 87Clyne, Michael A. A. . i91, 783, 838, 2178, Fyfe, Colin A. : . . 2269Cohen, Mendel D. . . , . 2155 Gaines, A. F. . . . . . 524Cooke, Brian J. . . . . . 679 Gait, P. D. . . . . 417Craig, Bruce B. . . . . . 1259 Gamlen, P. H. . * . . . 44629Briat, Bernard . . . . 268, 1441 Evman, E. . . 1957Brodsky, A. M. . . 1781 Falle, Howard R. : 200'1,2oi4,2oi9Bullock, Anthony T. . . . 469 Figari, Giuseppe . . . . 222242, 22530 AUTHOR INDEX-VOLUME 72, 1976Garner, A. . . .Garrington, D. C. .Geerlings, Paul .Giachardi, D. J. .Gianneschi, Leon P. .Gilson, Denis F. R. .Goggin, Peter L.Golde, Michael F. .Good, E. A. M.Gowenlock, Brian 'G.:Green, Jennifer C. .Greffe, Jean-Louis .Griffiths, Trevor R. .Grinter, Roger .Guerrero, Manuel I. .Guest, Martyn F. .HHHHHHHHHHHHHHHHHHHHallam, Harry E. .arold-Smith, Duane .hrris,G.W. .arris, Robin K.auge, R. H. .hwkes, Geoffrey E. ..eatley, F.:echt, Anne Marie .[icks, C. P. .Ell, H. Allen 0.511, N. J. .5tchman, Michael A.[olt, smith L. .[oneybourne, Colin L.[oward, Christopher B.[oward, Joseph .[yde, Robert G.[ubbard, Hugh V. St. A.[udson, Andrew .[ussein, M. Ali .lsobe,Taro .Israelachvili, Jacob N. .Iwaizumi, Masamoto .Jasinski, Jerry P. .Jenkins, H. Donald B. .Jennings, Barry R. .Jennings, K. R. .Jonathan, Neville .Jones, David E.H. .Jones, W. Jeremy .Jonsson, Bengt-Orjan .Jose, C. I. .Jotham, Richard W.I(ahn, Oliver .Kana'an, Adli S. .Kasrai, M. . .Keavey, Rosemary P.Kemeny, Gabor .Ken, Carolyn M. L.Kettle, Sidney F. A.Kharkats, Yu. I. .Kim,MinG. .King,F.W. .Kmg, T. A.Kiselev, A. V. .Kishi, Takashi .Klasinc,Leo .I(eMedy, John D.PAGE . 1010. 1482. 715619 : 1622,2095. 1673. 10252055'865, 927, 984. 988. 988. 2024. 765. 1860. 1970. 539. 1. 2269. 619. 2291. 1991. 1365. 2164. 439423 : 1267, 1494. 631. 54. 1304. 34. 469. 513. 571. 765855 : 686,693. 113. 1525. 113PAGEKornyshev, A. A. . 361Kosmus, Walter . 802Kronberg, Bengt . : 16j3, 1686Kroner, Jurgen . . 2283Kurucsev, Thomas .. . 2095Lappert, Michael F. .Leadbetter, Alan J. .Leclerc, Jean-Claude .Ledger, Michael B. .Lee, Edmond .Lestrade, Jean-Claude .Levine, S. .Lewis, Colin .Lind, Johan .Lindon, John C.Linnett, John W. (the late)Lister, David G. .Lloyd, D. Robert .Long, D. A. .Loudon, Alexander G. .Lowe, Susan E. .Luckhurst, Geoffrey R.Ludman, Clifford J. .Lynch, Roderick J. .. . . 539. 2205. 755,759. 883. . 1385. 1231. 501. . . 1851906' 1365, 14361298, 1503, 2233 . . 920807, 1036* 313, '865, 927, 984. 871920 : 651, 996, 1340. . 1741, 1759. 198064i, 1281, 1288,Maccoll, Allan . 871McDermid, I. Stuart . : : 2242,2252McEwan, Murray J. . . 183McFarlane, William . 1653McIlroy, Douglas K. . : 590, 2195Mclauchlan, K.A. . 87MacLean, C. 63, 1636McVicker, Elizakth . 2291Maddock, A. G. . . 257Madsen, H. E. Lundager : 527Magnasco, Valerio . . 22, 508, 1021Malcolme-Lawes, David J. . . 878Malecki, Jerzy . . . 104, 1214Mansell. P. I. . . . . . 426McKinley, J. M. . 143- 1304 Margrave, J. L. . . . . . 1991. 1569 Mark, Franz . . . 4631730 Marks, John A. . . . 125+ 700 Marshall, E. J. . . . . 830. 597, 1385 Martini, G. 3 24398, 1397, 1406, 1421 Mason, David P. . : 590, 2195 - . 207 Mason, Joan . . . . 2064906 1 1721,2191. . 125. 268, 1441 . . 1991. . 257 . . 773. . 1025. . 1653 . . 552. . 125 . . 361. . 934 . . 225 . . 1473 . . 950 . . 113 . . 1240Matheson, Andrew J. . . . 679Meriaudeau, Paul . . 472Millar, Donald .. 724Millen, D. James . 686, 693Mines, Geoffrey W. : : . . 686Mink, Janos . . . . 1025Mitchell, D. John . : 1525, 1613Molera, M. 3. . 1469Momicchioli, Fabio 887Morris, Alan . . 597, 814, 1385, 2225Morrison, Graham . . 1970Moutran, Rafik . . 1447Murphy, David . . 135, 1221Matthews, Anthony P. . . . 579Metcalfe, John . . . 1574Miller, A. . 435Mirsky, Kira . 2155Mishra, Shuddhodan P. 747MUSSO, G. F. . . . . . 102Nachbaur, Edgar .Navascuhs, G. . .Neilson, J. Duncan .Ninham, Barry W. .Nip, Wing S.North, Alastair M:O'Connor, Charles J. .Ogilvie, J. F. . .Ogryzlo, E. A. . .Ong, Kean Ghee . .Orchard, Anthony F. .Orrell, Keith G.O'Shea, Terence A. :Ottaviani, M. FrancescaOwen, Noel L. .Ozgen, G. .Ozgen, I.T. . .Pakiari, AIi €3. .Pattengill, M. D.Patterson, DonaldPedley, J. Brian .Pedulli, G. F. .Peel, J. BarriePethrick, Richard A.Petropoulos, J. H.Pfab, JosefPhilbrow, John R.'Philipson, N. A. .Phillips, David .Phillips, Leon F. .Pierens, Raymond K.Pilling, M. J. .Piper, Lawrence G.Polanyi, J. C. .Porter, Sir GeorgePoshkus, D. P.Potts, Anthony W:Prabhumirashi, L. S.Price, Alun H. .Quinn, Charles M. .Raie, M. . .Ramdas, SubramaniamRandiC, M.Rao, C. N. RamachandraRatcliffe, Christopher I.Reynolds, P. A. .Rice, Stephen A.Richardson, Frederick S,Richardson, Neville V. .Richmond, Peter .Rietveld, G. A. .Ripmeester, John .Rivail, Jean-Louis .Roberts, J .Roberts, P. J. .Roberts, R. Geoffrey .Robertson, Gerald N..Rodgers, Michael A. J.Roussis, P. P.Rowlinson, John S.Sadaoka, Yoshihiko .Sakai, Yoshiro .AUTHOR INDEX-VOLUME 72, 1976 31. . 802 Salmon, G. Arthur . 883,2001,2014,2019 . . 2035 Salt, D. W. . . . 76 . . 557 Schiff, H. I. . . . . 2075 . . 15i3, 1525 Schmickler, W. 307 . . - 838 Schmidt, Parbury P. 143, 17i, 1048, 106i, 1074, . . . 1957 1099, 1125, 1144,1736Schreiber, J. L. . . . . 897 . - 565 Schwartz,Robert W. . . . . 565. . . 183 Semkow, Andrew M. : . . 1298, 1503 - . - 1045 Setaka, Morio . * . . . 1340 . - 941 Sham,TsunK. . . . . . 1706 . . 1980 Sharma, R. R. . . . 91 3 . . . 324 Sharma, ShivK. . . . 848, 1344,2069. . 524 Shehfeh, M. A. . . . . 807. 524 Sheppard, Norman . . . . 707641, 1281, 1288, 1298 $hemood, Peter M* A* .. 1791, 1805 . . 897 Sik, Vladimir . . . . 941 . 16j3, 1686 Simm,I. G. . , . 426, 860 . . . 539 Simmie, J. M. . . . 417. . . 651 Simpson, C. J. S.'M. : . . . 417 . . 571 Smart,Roger St. C. . 707. 1957 Smith, Ian W. M. . : 288, 299, 1459. 737 Smith, John A. S. . . . . 1980988 Smith, John G. . . . . . 2298 : 481, 495 Smith, P. M. . . . 2205 . . 830 Smith, Thomas,D. . . . 481,4951574 Snook, Ian . . . . . 216183, 2082 So, S. P. . . . . 646. 724, 2108 Somayajulu, Gollakota R. . . . 2213. . 2178 Stocco, Gian-Carlo : . . . 1045, . . 897 Stoneham, A.M. . . . 913 . 511 Stradling, Roderick S. . . . . 871. 950 Street, Joan M. . . . . 1365. 1892 Suh, I. S. . . . 257. . . 1721 Symons, Martyn C. R. . , . j47, 820 . 1447Tan, Leok Peck . . . . 2233 . 1036 Tellinghuisen, Joel .. . . 783Thiebaut, Jean-Marie . . . . 2024. . 257 Thomas, JohnM. . . 12511251 Thornton, Geoffrey . . . 1045 : 232, 244 Tomkinson, John . . . 528, 1245988 Treadaway, M. F. . . . . 1473 mi, 1759 1821 Treweek, Roger F. . . . . 855. 1603 Tsarevsky, A. V. . . . . 1781. 792 Tucker, JohnN. . . . . . 1661. . . 331 Turnbull, A. . . . 2205. 1036 Turtle, Philip C. . . . . 1885PAGF PAGE. . 1603 Scrivens, James H. . . . . 2164 . - 2075 Sears, Trevor . . 597. 351 Sharp, Graham J. . . . . 539Shepherd, T. Maurice . . . 557. 792, 830 Stauffer, D. . . . 13541846, 1935 Trinajstit, N. . . . . . 244773, 1584,. .. .. .. 379, . 379,161316362269202465 1807126711531259737197019111911Vallini, G..Van Alsenoy, Christian .Van Megen, William .Vedrine, Jacques C. .Velthorst, N. H. .Vidaud,P. H. . .von Engel, A.Vorotyntsev, M. A. :Vos, H. w.Waddington, Thomas C.Walker, Isobel C.1759,. . . 1021. . . 715 . . 21647263, 1636. . . 1185 . . . 1185 . . 361. 63, 1636513, 528, 1245, 1741,1821, 1840, 1935, 1980 . . . 21032Wandelt, B.Ware, William R.Wargon, Jorge A.Waring, Stephen .Watanabe, HiroshiWatari, Fumiowatkins, Steven F.Wayne, R. P. .White, J. W. .Wilkinson, FrankWilliams, David .Williams, FfranconWilliams, GrahamWilliams, Terence A.AUTHOR INDEX-VOLUME 72, 1976PAGE . . . . 1957 . . . . 1851 . . . 552 . . . 1 . . . 1730 . . , . 113 . . 565. . 435, 439,446. . . 604, 1010. . . 1267, 1494 .. 552. . 1447, 1482,2171. . . 1892. . &I, 1185Woodcock, Leslie V.Wrackmeyer, BerndWright, C. J. .Yaron,M. . .Yarwood, Jack .Yeates, R. N. .Yee, Kim. K. .?arb-Adami, NoelZivkovit, T. .Zundel, GeorgZwolinski, Bruno J.PAGE . . . . 731 . . , . 2283 . . . . 513. . . . 1185 . , . 967 . . . 996 . . . . 2113. . 1267, 1494 . . . 244. 2127. 221THE FIFTH ANNUAL GENERAL MEETING OF THE FARADAY DIVISION of The ChemicalSociety was held at 9.00 a.m., on 9th September 1976, in the Molecular Sciences Lecture Theatre,The University of Sussex, with Professor D. H. Everett, M.B.E., M.A., D.Sc., C.Chem., F.R.I.C.,in the Chair.MinutesThe Minutes of the Fourth Annual General Meeting of the Faraday Division, which had beencirculated previously, were taken as read and confirmed.Annual ReportDuring 1975 the Faraday Division held two General Discussions and one Symposium.Thefirst Discussion, No. 59 on ‘Physical Adsorption in Condensed Phases’ was held at the Universityof Bristol in April and attracted more than 150 participants including 35 from overseas. Thesecond Discussion, No. 60, on ‘Electron Spectroscopy of Solids and Surfaces’ was held at theUniversity of British Columbia, Vancouver, Canada in July and was the 5th Faraday Discussionto be held in North America since 1952. About 170 participants attended the Discussion in-cluding 35 from outside North America and 55 from the U.S.A. The Division was indebtedto Professor McDowell for the initial invitation to visit Canda, and to him and his CanadianOrganisation for their most successful efforts in obtaining financial support from the Universityof British Columbia, The Chemical Institute of Canada, Physical Chemistry Division, NorthAmerican industry (viz.Atomic Energy of Canada, Canadian Marconi Company, Dow ChemicalCompany, Dupont of Canada, Fisher Scientific Company, Imperial Oil Ltd., National ResearchCouncil, Research Corporation of America), and the Government of British Columbia. TheFaraday also recorded its grateful thanks to the Royal Society for a generous contributiontowards the travel expenses of the European participants. Symposium No. 10 on ‘ProtonTransfer’ was held at Stirling in September and coincided with the retirement of Professor R. P.Bell who opened the meeting with the 17th Spiers Memorial Lecture entitled ‘The Developmentof Ideas about Proton Transfer Reactions’.150 participants were present at the Symposiumincluding over 50 from overseas.In addition to the published meetings the Division was also represented at the Annual Congressat York, in April, where a Symposium was arranged jointly with Perkin Division and E.S.R.Group on ‘Electron Spin Resonance Spectroscopy of Free Radicals’ and at the Autumn Meetingin Reading where an informal discussion on ‘Interpretations of the Properties of NaturallyOccurring Multicomponent Solutions such as Sea Water and Body Fluid’ was held. An informalhalf day meeting was arranged in London on ‘Pliotogalvanic and Photovoltaic Aspects of SolarEnergy Conversion’ and the Division collaborated with the Institute of Physics on a meeting on‘Interatomic Forces in Condensed Matter’ held at Reading in April.The 1975 Bourke Lectures entitled ‘Kinetic Information from Chemical Lasers’ were given byProfessor G.C. Pimentel (University of California, Berkeley, U.S.A.) at the Universities ofCardiff, Reading and Heriot-Watt. The Centenary Lecture by Professor R. Hoffmann (CornellUniversity, U.S.A.) on ‘Theoretical Aspects of Penta-Coordination’ was allocated to the Faradayand Dalton Division and was given at a half-day Symposium in London.The Marlow Medal for 1975 was awarded to Dr. G. Duxbury (University of Bristol) for hiscontributions to many aspects of experimental and theoretical spectroscopy.It was with great regret that Council recorded in November, the death of Professor J.W. Linnett,F.R.S. Professor Linnett was the last President of the Faraday Society and the first Presidentof the Faraday Division. At the time of his death he was a Vice-president of the Division andthe President Elect of The Chemical Society.In 1975 the eight subject groups affiliated to the Division continued to make valuable contri-butions by arranging specialist group meetings which included meetings on the following topics:Applications of Lasers in Chemical Kinetics (Gas Kinetics Group)Phase Separation and Phase Equilibrium in Polymer Solutions (Polymer Physics Group)The Hydrogen Economy (Electrochemistry Group34 ANNUAL GENERAL MEETINGPotential Energy Surfaces (Theoretical Chemistry Group)Surface Science (Surface Reactivity and Catalysis Group)Rheometry (Polymer Physics Group)Molecular Spectroscopy and Neutron Scattering (Neutron Scattering Group)Electrochemistry of Lead (Electrochemistry Group)Excitations of Surfaces and Adsorbed Molecules (Neutron Scattering Group)International Symposium on Gas Kinetics (Gas Kinetics Group)Molecular Beams (Molecular Beam Kinetics Group)Polymers at the Liquid-Solid Interface (Colloid and Interface Science Group)Chemisorption and Catalysis (Surface Reactivity and Catalysis Group)Organic Electrochemical Synthesis (Electrochemistry Group)Novel Electrode Materials (Electrochemistry Group)Pseudo Potentials (Theoretical Chemistry Group)Electrical Methods of Machining, Forming and Coating (Electrochemislry Group)Diffuse and Small-angle Neutron Scattering from Disordered Materials (Neutron ScatteringSpin Waves (Neutron Scattering Group)Mass Transport in Ceramic Materials (Electrochemistry Group)The Structure and Dynamics of Liquids (Neutron Scattering Group)Group)Membership of the Division in 1975 was 4,363 comprising 2,903 U.K.members and 1,460 membersfrom overseas.Faraday Division Newsletter No. 2 was distributed to members with the February issue of‘Chemistry in Britain’.3 Treasurer’s ReportThe Treasurer reported on the action taken by Council following the resolution passed in 1975‘that Council be requested to seek an increase in the allocation of funds to the Faraday Divisionfor the organising of conferences’.At the time of the resolution, it had not been possible toincrease the funds because all Divisions had agreed to freeze expenditure at the 1974 level for aperiod of 3 years. However, that period was over in 1976/7 and a request by all Divisions for a50% increase in the allocation to the Divisions Committee had been granted and a decision onthe allocations to individual Divisions was awaited. In the meantime, it had been possible toincrease by 50 % the sum available to Organising Committees following a decision that the incomefrom the sale of preprints be accrued to the Faraday Division.In 1976, it had also been agreed that a Division making a saving against its ‘other cost’ budgetwould be allowed to carry forward to the following year, half the saving achieved up to a maxi-mum of half the annual allocation to the Division.4 Elections to CouncilThe members of the Council of the Faraday Division of The Chemical Society to take office fromMarch 1977 were as follows:PresidentPROF.D. H. EVERETT, M.B.E., M.A., D.Sc., C.Chem., F.R.I.C.Vice-presidents who have held ofice as PresidentPROF. C.E.H.BAWN, C.B.E.,Ph.D.,F.R.S. D~.T.M.SUGDEN,C.B.E.,M.A.,S~.D.,C.C~~~.,PROF. G. GEE, C.B.E.,Sc.D., C.Chem.,F.R.I.C.,PROF. SIR GEORGE PORTER, M.A., Sc.D.,F.R.I.C., F.R.S.F.R.S.C.Chem., F.R.I.C., F.R.S.PROF. R. P. BELL, M.A., C.CHEM., F.R.I.C.,F.R.S., F.R.S.E.Vice-Presiden tsPROF. A. D. BUCKINGHAM, M.A., Ph.D.,PROF. P. GRAY, M.A., Sc.D., C.Chem., F.R.I.C.PROF. M. MAGAT, D.Sc., D.Phi1.PROF.J. S. ROWLINSON, M.A., D.Phil., C,Chem.,DR. H. A. SKINNER, B.A., D.Phil., C.Chem.,PROF. F. C . TOMPKINS, DSc., C.Chem.,PROF. D. H. WHIFFEN, M.A., D.Phil., D.Sc.,C.Chem., F.R.I.C., F.R.A.C.I., F.R.S. F.R.I.C.F.R.I.C., F.R.S.F.R.I.C., F.R.S. C.Chem., F.R.I.C., F.R.SANNUAL GENERAL MEETING 35Ordinary MembersDr. W. J. Albery, M.A. D. Phil.Dr. J. H. Baxendale, D. Sc.PROF. MANSEL DAVIES, Sc.D., C.Chem., F.R.I.C.DR. W. J. DUNNING, M.B.E., Ph.D., C.Chem.,PROF. F. FRANKS, D.Sc., C.CHEM., F.R.I.C.DR. D. N. HAGUE, M.A., Ph.D., C.Chem.,DR. G. R. LUCKHURST, PH.D.PROF. A. M. NORTH, D.Sc., F.R.S.E., C.Chem.,DR. B. A. THRUSH, M.A., Sc.D.DR. D. A. YOUNG, D.Sc., M.INsT.P.F.R.I.C.F.R.I.C. F.R.I.C.Honorary SecretaryPROF.F. C. TOMPKINS, D.Sc., C.Chem., F.R.I.C., F.R.S.Honorary TreasurerPROF. P. GRAY, M.A., Sc.D., C.Chem., F.R.I.C.The President thanked Professor W. C. Price, Professor N. B. H. Jonathan, Professor I. M.Mills, Dr. R. Parsons and Dr. B. A. Pethica, the retiring members of Council, for their services.5 Future ActivitiesThe President reviewed future activities of the Faraday Division and drew attention to the increasein Divisional activities since amalgamation. A full programme of Discussions and Symposiawas planned for 1977 and the Division would also contribute informal discussions to the Annualand Autumn Meetings of the Society. In addition to the Bourke Lectures by Professor R.Gordon (Harvard), the Division would also be allocated half-day Symposia arranged aroundendowed lectures of the Society and the President reminded members that these were Faradaymeetings and urged them to encourage colleagues to support them.Council was continuing to collaborate with other Societies; the second of the biennial JointMeetings with the Deutsche Bunsen Gesellschaft, the SocietC de Chimie Physique and theAssociazione Italiana di Chimica Fisica was to be held in Germany in 1976 and the third wasplanned for France in 1978.Also, two meetings sponsored jointly with the Institute of Physicswere to take place in September 1977.Professor Murrell proposed that members of the Division be reminded that they were invitedto suggest topics for Discussions and it was agreed that a notice to this effect should appear inthe Faraday Transactions and in ‘Chemistry in Britain’NOTICES TO AUTHORS-NO.7/1970Deposition of Data-Supplementary Publications SchemePreambleThe growing volume of research that produces large quantities of data, the increasing facilitiesfor analysing such data mechanically, and the rising cost of printing are each making it verydifficult to publish in the Journal in the normal way the full details of the experimental datawhich become available. Moreover, whilst there is a large audience for the general methodand conclusions of a research project, the number of scientists interested in the details, andin particular in the data, of any particular case may be quite small. The British LibraryLending Division (B.L.L.D.) in consultation with the Editors of scientific journals, has nowdeveloped a scheme whereby such data and detail may be stored and then copies madeavailable on request at the B.L.L.D., Boston Spa.The Chemical Society is a sponsor ofthis scheme and has indicated to the B.L.L.D. its wish to use the facilities being madeavailable in this “Supplementary Publications Scheme”.Bulk information (such as crystallographic structure factor tables, computer programmesand output, evidence for amino-acid sequences, spectra, etc.), which accompany paperspublished in future issues of the Chemical Society’s Journal may in future be deposited,free of charge, with the Supplementary Publications Scheme, either at the request of the authorand with the approval of the referees or on the recommendation of referees and the approvalof the author.The SchemeUnder this scheme, authors will submit articles and the supplementary material to theJournal simultaneously in the normal way, and both will be refereed.If the paper is acceptedfor publication the supplementary material will be sent by the Society to the B.L.L.D. whereit will be stored. Copies will be obtainable by individuals both in the U.K. and abroadon quoting a supplementary publication number that will appear in the parent article.Preparation of MaterialAuthors will be responsible for the preparation of camera-ready copy according to thefollowing specifications (although the Society will be prepared to help in case of difficulty).(a) Optimum page size for text or tables in typescript: up to 30 cm x 21 cm.(b) Limiting page size for text or tables in typescript: 33 cm x 24 cm.(c) Limiting size for diagrams, graphs, spectra, etc.: 39 cm x 28.5 cm.( d ) Tabular matter should be headed descriptively on the first page, with column headings(e) Pages should be clearly numbered.recurring on each page.It is recommended that all material which is to be deposited should be accompanied by someprefatory text. Normally this will be the summary from the parent paper and authors willgreatly aid the deposition of the material if a duplicate copy of the summary is provided.If authors have the facilities available the use of a type face designed to be read by computersis encouraged.DepositionThe Society will be responsible for the deposition of the material with the B.L.L.D. TheB.L.L.D.will not receive material direct from authors since the Library wishes to ensurethat the material has been properly and adequately refereed.3Action by the SocietyThe Society will receive a manuscript for publication together with any supplementarymaterial for deposition and will circulate all of this to referees in the normal way. Whenthe edited manuscript is sent to the printers the supplementary material will be sent fordeposition to the National Lending Library who will issue the necessary publication number.The Society will add to the paper, at the galley proof stage, a footnote indicating whatmaterial has been deposited in the Supplementary Publications Scheme, the number ofpages it occupies, the supplementary publication number, and details as to how copies maybe obtained.AvailabilityCopies of Supplementary Publications may be obtained from the B.L.L.D.on demand byorganisations which are registered borrowers. They should use the normal forms andcoupons they use for all requests. Others may obtain them at the rates shown below.Costs include postage (airmail where available). Cheques should be made payable to‘The British Library’. Hard copy will normally be provided.United Kingdom 5p per pageEurope 21.25 per 10 pagesOutside Europe 21.65 per 10 pages.Pro forma invoices are sent in all cases where normal forms and coupons are not used.All requests for Supplementary Publications should be addressed as follows :M.J. P. Chillag,British Library Lending Division,Boston Spa,Wetherby,West Yorkshire LS23 7BQ,United Kingdom.In all correspondence with the B.L.L.D. or the Society authors must cite the supple-ment ary publication number.International CollaborationA similar scheme (known as the National Auxiliary Publications Service) is being operatedin the U.S.A. by the American Society for Information Science. Similar schemes are alsobeing contemplated in other countries. The provision of reciprocal arrangements for theexchange of supplementary data between the various national deposition centres is beinginvestigated.3NQTICE TO AUTHQRS-NQ. 911974NomenclatureFor many years the Society has actively encoxaged the use of standard I.U.P.A.C.nomenclature and symbolism in its publications ;IS an aid to the accurate and unambiguouscommunication of chemical information between authors and readers.Although theJ.U.P.A.C. rules for naming organic compounds have now gained wide acceptance amongstchemists, mainly because they have been in existence for a number of years, those for naminginorganic compounds are of more recent origin and for this reason their acceptance is lessgtneral .In order to encourage authors to use I. U.P.A.C. nomenclature rules when drafting papers,atkntion is drawn to the following publications in which both the rules themselves andguidance on their use are given.‘Nomenclature of Qrganic Chemistry, Sections A, B, and C’, Butterworths, London,‘Nomenclature of Inorganic Chemistry’, Butterworths, London, 1971.‘Manual of Symbols and Terminology for Physicochemical Quantities and Units’,In addition to the above publicatioiis, provisional rules for the naming of organometalliccompounds, amino-acids, carbohydrates, carotenoids, and steroids, and rules of stereo-chemistry are available from the:2nd Edition, 1971.Butt erwor t hs, London, 1 970.I.U. P.A. C. Secretariat ,Bank Court Chambers,2-3 Pound Way,Cowley Centre,OXFORD OX4 3 Y F .It is recommended that where there are no I.U.P.A.C. rules for the naming of particularcompounds or authors find difficulty in applying the existing rules, they should seek theadvice of the Society’s editorial staff.3NOTICE TO AUTHORS-NO. 10/1976Authentication of New Compounds(1) It is the responsibility of authors to provide fully convincing evidence for the homo-geneity and identity of all compounds they claim as new.Evidence of both purity andidentity is required to establish that the properties and constants reported are those of thecompound with the new structure claimed.(2) In the context of this Notice a compound is considered as new (a) if it has not beenprepared before, (b) if it has been prepared before but not adequately purified, (c) if it hasbeen purified but not adequately characterised, ( d ) if, earlier, it has been assigned an erroneousconstitution, or (e) if it is a natural product synthesised for the first time. In preliminarycommunications compounds are often recorded with limited characterising data ; in spiteof (c) above later preparations of such compounds are not considered as new if the propertiespreviously reported are confirmed ; the same applies to patents.*(3) Referees are asked to assess, as a whole, the evidence in support of the homogeneityand structure of all new compounds.No hard and fast rules can be laid down to cover alltypes of compounds, but the Society’s policy remains unchanged in that evidence for theunequivocal identification of new compounds should normally include good elementalanalytical data ; an accurate mass measurement of a molecular ion does not provide evidenceof purity of a compound and must be accompanied by independent evidence of homogeneity.Low-resolution mass spectroscopy must be treated with even more reserve in the absence offirm evidence to distinguish between alternative molecular formulae. Where elementalanalytical data are not available, appropriate evidence which is convincing to an expert inthe field will be acceptable, but authors should include, for the referees, a brief explanationof the special nature of their problem.(4) Spectroscopic information necessary to the assignment of structure should normallybe given. Just how complete this information should be must depend upon the circum-stances; the structure of a compound obtained from an unusual reaction or isolated froma natural source needs much stronger supporting evidence than one derived by a standardreaction from a precursor of undisputed structure. Authors are reminded that full spectro-scopic assignments may always be treated as a Supplementary Publication where theirimportance does not justify their inclusion in the published paper.(5) Finally, referees are reminded of the need to be exacting in their standards but at thesame time flexible in their admission of evidence. It remains the Society’s policy to acceptwork only of high quality and to permit no lowering of present standards.* New compounds should be indicated by underlining the name (for italics) at its first mention(excluding headings) in the Experimental section only, and by giving analytical results in the form :(Found: C, 63.1 ; H, 5.4. C13Hi3N04 requires C, 63.2; H, 5.3 %). If analytical results forcompounds which have been adequately described in the literature are to be included, they shouldbe given in the form : (Found : C, 62.95 ; H, 5.4. Calc. for C13H13N04 : C, 63.2 ; H, 5.3 %).Analyses are normally quoted to the nearest 0.05 %.3Publication of Theoretical and Computational PapersThe Primary Journals Committee has been considering future policy towards the publicationof papers with a heavily computational content, particularly where these involve standardmethods, such as semi-empirical or ab initio calculations of molecular electronic propertiesusing readily available computer programs. Many such papers report what would be con-sidered ‘routine work’ in other areas of chemistry and have often included extensive detail.A specialist sub-committee formulated a set of proposals which were circulated to a largerepresentative sample of theoretical chemists and met with general acceptance. These, withthe comments on them, form the basis of this notice.The Primary Journals Committee recognises that computational work can play a valuablerole in chemistry, and will probably continue to do so on an increasing scale. It accepts thetime-honoured principle that the first criterion for publication of a paper by the Societyshould be the worthiness of the chemical problem considered, rather than the particulartechniques employed by the author. For example, the use of a new computing algorithm,or the modification of a program, would not usually, on its own, provide sufficient justificationfor publication.The Primary Journals Committee recommends to authors the following guidelines for thepreparation of computational papers, so that the material can be presented concisely andeffectively.(i) Papers should be submitted to the appropriate journal: a paper containing in-novations in theory to Faraday Transactions 11, one in which the computations areincidental to the chemistry to Perkin, Dalton or Faraday I Transactions. Papersconcerned mainly with computational details are unlikely to be accepted.(ii) The purpose of the paper and the precise objectives of the calculations performedshould be clearly stated: the results obtained should be reported only in so far asthey relate to those objectives.(iii) Many papers use a routine procedure based on a well documented method, be itsemi-empirical or ab initio. It is then sufficient to name the particular variant,referring to key papers in which the method was developed, to cite the computerprogram used, and to indicate briefly any modification made by the author. Areview of theoretical background would be out of place, but an author should saywhy he considers the method adequate for his purposes.(iv) Extensive tabulation of numerical results, such as the magnitudes of atomic orbitalcoefficients, electron populations, contour maps of molecular orbitals and electrondensities, and peripheral material of a similar nature, is normally unnecessary.Lengthy line-by-line discussion of such material is, as a general rule, quite unaccep-table. Where an author considers that there is a special need to make such materialavailable to other workers, as with highly accurate computations, for example,then this may be deposited with the British Library as a Supplementary Publication.Such material should be submitted with the main paper, clearly distinguished fromit, and referred to in the main text.Guidelines can never provide sufficient criteria for acceptance or rejection of a paper.Critical assessment of the theoretical methods used in a computation, and of their suitabilityfor the purpose in hand, will continue to be entrusted to specialist referees who must alsodecide whether the results are new and advance science.4

ISSN:0300-9599    

DOI:10.1039/F197672BA001

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Single-pulse Shock Tube Studies of Hydrocarbon PyrolysisPart 5.-Pyrolysis of NeopentaneBY JOHN N. BRADLEY* AND KENNETH 0. WESTDepartment of Chemistry, University of Essex, Colchester, EssexReceived 29th January, 1975The thermal decomposition of neopentane has been studied in the single-pulse shock tube over thetemperature range 1030-1300 K. The experimental results are fully explained by the generalizedmechanism for alkane pyrolysis proposed by Bradley (Proc. Roy. Suc. A, 1974, 337, 199) providedthe same special features are included i.e. " forbidden " radical isomerizations, hydrogen atom attackon olefins, and '' high " rates for methyl radical abstraction reactions. Optimization by computerof the critical reaction parameters leads to the following rate constants(1)CH3+CSH12 + CH4+CSH11 (2)H+ C4Hs -+ C4H9 (14)neo-C5H12 -+ t-C4H, + CH3k, = 3.3 x 1OI6 exp( - 336 kJ mol-'/RT) s-lkz = 6.6 x 10" exp( - 90 kJ moI-'/RT) dm3 mol-' s-lkI4 = 1.6 x 1O'O exp( - 6.3 kJ rn~l-~/RT) dm3 mol-I s-IThe reaction behaviour is also sensitive to the reactionsCH3 + C4Hs -+ CH4 + CIH, (19)C4H9 -+ C3H6 + CH, (6)C4H9 + CzH4+CzH5 (32)although absolute rate constants obtained for them cannot be regarded as reliable.A general mechanism for the pyrolysis of alkanes at high temperatures has beenproposed previously, using isobutane as an appropriate hydrocarbon to test thearguments.The experimental technique and the computational procedures havesince been improved and the investigation has been extended to neopentane.Neopentane was selected because, as with isobutane, there is only one likelyinitiation step, i.e.,CH3 CH3I II ICH3 CH3CH3-C-CH3 + CH3-C* + *CH3but it is somewhat simpler than isobutane in having all its hydrogen atoms identical.The absence of any additional complexities means that it provides an ideal test of themechanism proposed previously and particularly of the importance of the " forbidden "modes of radical decomposition.EXPERIMENTALThe apparatus and experimental procedure have been described in previous papers inGeneral purpose grade neopentane (>98 %), supplied by B.D.H.Ltd,, was purified bythe s e ~ i e s . ~ - ~J . N. BRADLEY AND K . 0. WEST 9bulb-to-bulb distillation in vacuo followed by preparative g.1.c.using an alumina column.G.1.c. analysis demonstrated that the purified neopentane contained less than O.OO0 1 % ofother C1-C5 hydrocarbons and mass spectral analysis showed that higher hydrocarbons didnot exceed 0.01 %. Experiments were conducted with mixtures of 0.1, 0.5 and 1.0 % neo-pentane in high purity argon. For some runs 100,500 or 10oO p.p.m. of oxygen were addedto the 1 %mixtures.The experiments were conducted on all these m'xtures over the range 1050-1300 K. Thereaction times fell in the range 0.6-1.6 ms and reflected shock pressures in the range 300-400kN m-'.The products were analyzed by g.1.c. using a Porapak N column. This column wasunable to separate propane from propylene and absence of the former was confirmed bysplitting the product stream in two and analyzing one stream on an alumina colum.Integration of the kinetic equations by computer was carried out using the Gear predictor-corrector method as before, but in this case the integration procedure formed a sub-routine within an optimization program which manipulated the rate constants until a satis-factory fit to the experimental data had been achieved.This progrm is basically that devel-oped by Broyden for the solution of simultaneous non-linear differential equations, withmodifications by Dr. J. Ford of the Computing Centre, University of Essex. The mostimportant of these is that the rate constants are converted to trigonometric functions in orderto keep them within prescribed bounds. In this example, with about thirty rate equations andfive adjustable rate parameters, optimization typically required 80-100 iterations, with amaximum of about 200.RESULTSOverall rate constants for neopentane pyrolysis have been calculated from the lossof the parent hydrocarbon assuming reaction orders of 5, 1 and 3.No significant3.0nrl L-Y,--.-0rlM0 -2.00.8103 KIT1.0FIG. 1 .-Arrhenius plot of the apparent overall first-order rate constants for neopentane pyrolysis. +, 0.1 % neopentane ; x , 0.5 neopentane ; 0, 1.0 % neopentane ; V, 1 % neopentane with100 p.p.m. oxygen; A, 1 % neopentane with 500 p.p.m. oxygen; H, 1 % neopentane with 1OOOp.p.m. oxygen10 PYROLYSIS OF NEOPENTANEdifference could be detected in the standard deviations obtained by least-squaresanalysis of Arrhenius plots based on each of the three sets.An Arrhenius plot ofthe first-order rate constants is shown in fig. 1 and the data are fitted best by theexpression k = 2.88 x lo9 exp(- 159 kJ mol-'/RT) s-l although this should not betaken to imply that the reaction obeys first-order kinetics. Addition of oxygen tothe neopentane had no measurable effect on the nature and extent of the decomposi-tion although similar amounts are known to affect the pyrolysis of fluorinated hydro-carbons.The major products of the reaction were isobutene, ethane and methane, withsmaller quantities of allene, methylacetylene, propylene, acetylene and ethylene. Noattempt was made to analyze for hydrogen although mass balance considerations showthat it must have been formed.At conversions greater than 50 %, minor quantitiesof pentene and of isobutane were also detected. The amounts were too small to allowidentification of the pentene isomers. The product yields changed with temperatureand to a lesser extent with time, the most significant change being the increase inconcentration of ethylene and propylene with temperature at the expense of theisobutene. These effects of temperature on the product yields are illustrated in fig. 2.20113M)0-I100 12000I ICO 1200temperature/KFIG. 2.-Variation of product yield with temperature at a constant reaction time of 1 ms.In the absence of a unique reaction order, any data averaging must be treated assuspect and for the purpose of subsequent analysis ten representative experiments wereselected which covered the range of the experimental conditions.All the experimentschosen were free from measurable shock attenuation and showed product recoveriesin excess of 90 % of the original reactant. These experimental data are listed intable 1J . N. BRADLEY AND K . 0. WEST I1COMPUTER SIMULATIONIn an earlier paper,l the following schematic mechanism for alkane pyrolysis wasproposed :initiation : R-R’ + R+R’(rupture of C-C only)(attack by CH3 and H on parent)propagation : CH3+RH + CH,+RH + RH + H2 + Rradical decomposition(to H or lower radical + olefin)ethane reactionsR -+ olefin+ R’H atom addition to olefins H+olefin + R.On this basis the detailed mechanism for neopentane pyrolysis can be represented byreactions (1) to (16) in table 2.As one of the main objectives of the present studywas to assess the importance of the so-called “ forbidden ” isomerizations, thesereactions were excluded from the mechanism in the first instance.tempera-turc/K1295126512301220120511801170114011301100TABLE 1 .-RESULTS OF EXPERIMENTS SELECTED FOR COMPUTER SIMULATIONreaction comer-timelms sion/% CH4 C2H4 C& C2H2 C3H6 C3H4-A C3H4-M i-Caa i-C4Hlo i-CsHlo1.05 58.3 8.9 14.7 16.3 1.9 5.5 10.5 11.5 29.6 0.8 0.31.1 51.7 7.6 9.4 16.8 1.6 4.5 9.0 7.5 43.1 0.4 0.10.85 25.7 5.3 3.0 16.8 0.7 2.0 4.5 2.2 65.0 - -0.7 16.5 4.7 1.9 16.7 0.3 1.5 2.9 1.2 70.8 - -0.8 15.4 4.6 0.9 16.1 0.2 0.9 1.5 0.6 75.2 - -1.0 14.6 4.9 0.4 15.5 0.1 0.6 1.1 0.2 77.2 - -0.95 32.9 5.8 4.0 17.1 0.9 2.8 5.1 3.7 60.6 - -1.2 24.5 5.3 1.8 16.1 0.3 1.3 3.1 0.9 71.2 - -0.9 14.2 5.3 0.4 15.2 0.1 0.6 1.0 0.2 77.2 - -0.6 6.1 4.9 0.2 15.2 - 0.3 0.4 - 79.0 - -The yields are quoted as percentages of the total quantity of neopentane decomposed.C3H4-A and C3H4- M denote allene and methylacetylene respectively.To avoid confusion, no attempt was made in the model to distinguish the con-centrations of the different radical isomers present.This means that C4H9 denotesboth t- and iso-species and C3H7 both iso- and n-species. This gives the mechanismadded flexibility and removes some unwanted “ degeneracy ” which arises whenseveral reactions lead to a kinetically-identical result.As it stands the mechanism is inadequate to explain the experimental results sinceit contains no routes leading to allene, methylacetylene and acetylene. Acetylenewas only a minor product and it seemed reasonable to make the assumption that itwould be formed either from ethylene, e.g., via the sequenceCH3 + C2H4 + C2H3 + CH4H+ C2H4 + C2H3 + H2C2H3 + C2H2 +H,or from a precursor of ethylene, e.g., via the ethyl radicalC2H5 + C2H3+H2CZH3 + C2H2 + H12 PYROLYSIS OF NEOPENTANERather than complicating the mechanism further, the small acetylene yield wastherefore added to the amount of ethylene formed.A corresponding assumption was not considered suitable to deal with the alleneand methylacetylene because of the larger quantities involved and it was thereforenecessary to incorporate in the mechanism a reaction sequence leading to C3H4, nodifferentiation being made between the two isomers. It is believed that C3H4 isformed from the product, isobutene, either by direct decompositionC4Hs -+ C3H5 +CH, (17)C3H5 -+ C3H4+H (1 8)TABLE 2.-sUMMARY OF REACTIONS AND RATE DATA USED IN INITIAL SIMULATION-13-14IIII111III1IIIII1133-1I1I1reactionAl Kassel(dm3 mol-1 s-1 or s-1) E/kJ mol-1 correction12 -+ C4H9+CH3 (1) 1 . 1 7 ~ 10171 -+ C4Hs+ CH3 (4) 1 .Ox 1014-I9 -+ C3Hs+CH3 (6) 1 .6 ~ 101437 4 C2H4-k CH3 (8) 4'0 x 101312 -+ CH++CSHl1 (2) 5 . 0 ~ 10"12 -+ Hz+CSHll (3) 1 . 0 ~ lo1'39 + Cq.Hs+H (5) 4 . o ~ 10133 7 -+ CsH6-I-H (7) 2 .0 ~ 10143 5 -+ CJI4+H (9) 3 . o ~ 1013H6 -+ CH4+CzHS (10) 5 . 0 ~ 10"& j -+ Hz+CzH5 (11) 1.oX 10"36 S CHjfCH3 (12,13) 5 . 0 ~38 C4H9 (14) 3 . 2 ~ lolo34 + C2H5 (16) 9 . 3 ~ 1O1O-+ C3H4+H (18) 3 . 2 ~ loz3H7 + C3H4+ CH3 (21) 1 .Ox lOI436 -+ C3H7 (15) 7 . 2 ~ 10938 -+ C3H5$CH3 (17) 6.3 X3 8 4 CH4+C4H7 (19) 5 . 0 ~ 10''38 Hz+C4H7 (20) 5 . 0 ~ 10''H6 -+ CH*+C3H5 (22) 6.3 X 10''k&j -+ 8 2 + CBHS (23) 5.0 X 10"12 4 C4H1o+CsHll (24) 5 . 0 ~ 10":12 -+ C ~ H ~ + C ~ H ~ I (25) 5 . 0 ~ 1O'l112 4 CZH6+C5Hll (26) 2 . 0 ~ 10'33 --* GHiz (27) 1.ox 10''33 * C4H10 (28) 1 . 0 ~ 1O'O34310915718013717313817038.589.938.56.35.011.737036720110920320.932.220.910910952.700or by the abstraction of hydrogenCH3 +C4H8 + C4H7 + CH4H + C4H8 -+ C4H7 +H,C4H7 -+ C3H4+CH30.9 --0.90.50.50.230.230.16--0.13i --0.50.23 --0.6----I --classIIII11111I11VVI11II1I, 1IVVIVIVII1I11VVIVVVVV(19)(20)(21)and both sequences were added to the reaction mechanism.Abstraction frompropylene was also included as a possible source, e.g.,CH3 + C3H6 -+ CH4 + C3H5 (22)H+C,H, -+ H P + C ~ H ~ . (23)Formation of C3H5 radicals directly from propyleneC3H6 + CSHS +J . N. BRADLEY AND K . 0. WEST 13is a much slower process becay$e it involves rupture of a C-H rather than a C--Cbond.Although previous work had demonstrated that attack by radicals other than Hand CH3 on the parent hydrocarbon was unimportant, it was considered desirable toreassess this hypothesis, particularly for C3H5, and reactions (24) to (26) representingattack by C4H9, C3H5 and CzH5 respectively were included in the initial analysis.In the same way, reactions (27) and (28), representing radical combination, wereincorporated even though the earlier work had illustrated that methyl radical combi-nation to ethane was the only reaction of this type which had to be considered.Rate constants for reactions (4), (5), (6), (7), (8), (9), (lo), (12), (f4), (15), (16),(22), (23) and (26) were taken directly from the references quoted in table 2.kl wasobtained by averaging the results of Tsang l4 and of Halstead et aZ.l Because of thepresent uncertainty in the rates of methyl radical abstraction reactions, k, was treatedas a variable throughout, the value quoted in table 2 merely serving as a suitablestarting point.k3 was estimated by combining the activation energy quoted by Trostand Steacie l6 with the pre-exponential factor for the corresponding reaction withi~0butane.l~ kl has been measured by several groups of workers and an averageof the literature values was emp10yed.l~’~~ k13 and k24 were derived from the corre-sponding forward reactions k,, and kl and the appropriate equilibrium constants.k17 has been measured in this laboratory : 2o separation into Arrhenius parameterswas achieved by estimating the activation energy from thermodynamic data. kl 8 andkZ1 were obtained by considering the entropy changes involved in the transition statein order to predict the pre-exponential factors, the activation energies being derivedfrom the overall thermochemistry. k19 and k,, were arbitrarily set equal to k, andkzo to k23.kZ7 and k28 were assigned the value of lolo dm3 mol-l s-l typical ofradical recombination reactions.The complete system was then integrated by computer for several sets of experi-mental conditions. For comparison with the experimental data, it was assumed thatmethyl radicals present at the end of the reaction time combined to form ethane : thiswas borne out by computer simulation of the expansion process. The other radicalconcentrations were sufficiently low to be neglected. Each rate constant in turn wasmultiplied by a series of factors between 50 and 0.02 and also by zero.Histogramsfrom the computations are illustrated in fig. 3 for a typical experiment conducted at1200 K with a reaction time of 900 p s . From such histograms it is possible to cate-gorize the importance of each step in terms of the classification suggested in theprevious paper :(I) reactions whose rates determine the overall kinetics ; (11) reactions which havelittle effect on the overall rate but influence the product distribution; (111) reactionswhose rates are unimportant, above a certain minimum, but are nevertheless essentialto the mechanism ; (IV) reactions which definitely occur but which have little influenceon the reaction; (V) reactions which do not occur to any significant extent.The classification obtained has been included in table 2.It will be immediately apparent that the arguments of the earlier paper (a) thatattack on the parent hydrocarbon by radicals other than CH3 and H, and (6) thatradical recombinations other than methyl + methyl are unimportant, are confirmed bythe present work.It is therefore possible to omit reactions (24) to (28) from furtherconsideration.The analysis also shows that the C3H4 compounds arise due to the abstractionof a hydrogen atom from the isobutene product (1 9) and (20) and do not involve eitherdirect decomposition of isobutene (17) or hydrogen atom abstraction from propylen14 PYROLYSIS OF NEOPENTANE(22), (23). It is worth commenting that all subsequent reactions of propylene appearto be unimportant although the same cannot be said of isobutene.It is thus possible to associate the characteristic reaction behaviour with the ratesof six reactions and to a considerable extent to correlate specific features with specificrate constants, thus :reaction (1) controls the overall reaction rate ; reactions (12) and (1 3) control themethyl radical concentration responsible for propagation ; reaction (2) controls thepropagation rate and the [CH,] yield; reaction (19) controls the [CH,] and [C,H4]yields ; reaction (14) controls the [C,H,] yield ; reaction (1 1) controls the [C,H4] yield.GOLO20030201001050302010030 r90 r7050302 1 6 8 10 12 1L 16 18 20 22 U 26 28reaction numberFIG.3.-The effect on the computed product yields of varying the values of the (non-optimized) rateconstants for a typical experiment at 1200 K with a reaction time of 900 ps (shaded area denotesx 10, open area denotes x 0.1).Attempts were then made to optimize the mechanism by varying the rate constantsk l , kZ, klz, k14 and kI9 until the computed yields of the major products matched thoseobserved experimentally. The rate of abstraction of a hydrogen atom from an alkanewas further assumed to be linearly dependent on the number of hydrogen atoms avail-able. k l l was then allotted a value equal to one-half the quoted value of k3 and k l J . N. BRADLEY AND K . 0. WEST 15was varied with k2 to maintain the relation k,, = 0.5 k2. k,, was tied to k12 viathe equilibrium constant.As with isobutane, all attempts failed to match the experimental yield of ethylene.The only way this problem could be overcome within the bounds of the mechanismwas to relax the constraint that kll should equal 0.5 k3.However optimizationrequired the quite unacceptable situation that kll should be two orders of magnitudegreater than k3 and even then the mechanism failed to account for the decrease inrelative yield of isobutene with temperature.The only acceptable solution was to permit the occurrence of "forbidden"isomerizations as in the isobutane pyrolysis. The available reactions areThe yield of pentene is quite sinall so that reaction (29) is unlikely to be of significance.Reactions (30) and (31) both generate C2 and C3 hydrocarbons in equal amounts andwould not provide the necessary " flexibility " in the ethylene yield.Reaction (32)serves the purpose admirably since it provides a unique source of ethylene : furthermorethe addition of hydrogen atoms to isobutene by reaction (14) generates radicals withexcess energy in two isomeric forms : t-butyl (CH3)3C- and isobutyl (CH3)2CHCH2*Rearrangement of excited isobutyl radicals certainly seems more feasible than the otherforbidden isomerizations.With the inclusion of k32 as an additional variable parameter, it was necessary tospecify the value of one of the other rate constants and that of k12 was chosen ashaving the most reliable literature value. It was then possible to determine rateconstant expressions for the six reactions which satisfied the complete set of experi-mental data.These are collected in table 3.TABLE 3 .-RATE CONSTANTS OBTAINED BY COMPUTER OPTIMIZATIONreaction rate constant expressionC5H12 -+ C4H9+CH3 (1) kl = 5 . 0 ~ 1015 expCH3+C5HI2 -+ CH4+C5H11 (2) k2 = 6 . 6 ~ lo1' expH+C4Hs + C4H9 (14) k14 = 1 . 6 ~ 1O'O expCH3+C4H8 -+ CH4+C4H7 (19) kI9 = 2 . 6 ~ loi3 exp(-318 kJrn~l-~/RT)s-l(- 90 kJ mol-'/RT) dm3 rnol-' s-'(- 6.3 kJ rnol-'/RT) dm3 rnol--l s-'(- 11 1 kJ rnoP1/RT) dm3 rnol-I s-'(- 92.1 kJ mol-l/RT)C4H9 3 C3H6+CH3 (6) kS2/k6 = 7 . 2 ~ lo3 expC4Hg -+ C2H4+ CzHS (32) }standarddeviationin loglo k0.1 10.220.290.820.12It should be noted that, as the number of variable rate constants in the computersimulation was chosen to match the quantity of independent experimental data avail-able, the fit was exact, i.e., to within the rounding errors.Uncertainty in the experi-mental measurmeents then appeared as scatter on the Arrhenius plots used to providethe complete rate constant expressions. The standard deviations listed in table 3shows that the rate constant expressions for k , , k , and k4 are very sntisfxtory bu16 PYROLYSIS OF NEOPENTANEthat the reaction for (19), which is a secondary reaction involving the olefin product,is far less reliable. It was possible to show that no other set of rate constants wouldfit the experimental data, assuming that the correct mechanism had been obtained.There is, of course, no way of demonstrating that the mechanism itself is unique,which is the reason why this particular approach has been adopted.Trace quantities of isobutane and pentene were observed at the highest tempera-tures.Computations showed that the former could be accounted for by reaction (24)provided k24 was about one-tenth the value of k2. This value seems reasonableconsidering the steric restrictions which inevitably accompany the reactions of t-butylradicals.Various routes to the pentenes are available. The simple radical recombinationsC3H5 +C2H5 + C5H10C4H7 +CH, + CSH10C3H7+C2H3 -+ C5H10were tested with rate constants of 3 x 1O'O dm3 mol-' s-l and failed to produce sig-nificant quantities of pentene. The isomerization of the neopentyl radical by reaction(29) is another possibility but seeins unlikely as the radical is not formed with excessenergy.A more probable route is via the addition of methyl radicals to isobutenewhich yields (CH3)2c CH2CH3 with excess energy in a reaction directly analogousto (14).CH3 + CH3--C=CH2 --+ CH3-C*-CH2-CHjI ICH3 CH3The three decomposition reactionsCH3-C-CH2-CH3 + CH2-C-CH2-CH3 + HI ICH3 C&1CH3ICH3+ CH3-C=CH-CH3 + H-+ CH3-C-CH2 + CH3all obey the P-bond breaking rule and if the first two are together responsible for 10 %of the total this would account for the yield of pentene observed.An attempt was made to simulate the small yields of acetylene by means of themechanismCH3 + C2H4 -+ CH4 + C2H3H + CzH4 --+ H2 + C2H3C2H3 + C2H2+Husing literature values for the first two rate constants 11* 21 of 2.0 x lo1' exp(-41.8kJ mol-l/RT) dm3 mol-l s-l and 1.82 x 1O'O exp( -27.6 kJ mol-l/RT) dm3 mol-' s-'respectively.As the mechanism contains no other reactions of C2H3, the third rateconstant may be chosen quite arbitrarily. It proved impossible to reproduce theacetylene yields even by increasing these rate constants by two orders of magnitude.It seems therefore that the alternative routesuggested in an earlier paperCZH, + C,H,+H,must be responsible for acetylene formationJ . N. BRADLEY AND K. 0. WEST 17DISCUSSIONThe most important conclusian of this work is that the mechanism proposed inthe investigation of isobutane pyrolysis applies to the pyrolysis of neopentane. Notonly is the same basic mechanism involved but also it is necessary to include the samethree types of process as before, i.e., radical decomposition via “ forbidden ” routes,methyl radical attack on alkanes with “ high ” reaction rates for such reactions, andaddition of hydrogen atoms to olefins.Although it is possible that other alkanes mayreveal particular problems, it is evident that the general mechanism for alkane pyrolysismay be considered proven. The work has alsO produced rate constants for six hightemperature reactions. Since the experimental technique has been refined followingthe previous work, the present findings should be more accurate.It is worth mentioning here that the previous paper implied a discrepancy of abouta factor of ten between the initiation rate of isobutane pyrolysis measured by thepresent technique and that recorded earlier by Konar, Marshall and Purnell.22 As0.8 1.0 1.2 1.410’K/TFIG.ci.-Comparison of rate constant reiations for the initiation reaction (1).this cast some doubt on the validity of the technique, it is reassuring that these authors 23have now reassessed their measurement and have reported a revised value for the ratetechnique which effectively removes the discrepancy.The optimization leads to a rate constant k, for the initiation reaction of neo-pentane pyrolysis of 5.0 x 10’ exp( - 3 18 kJ mol-’ /RT) s-l . This rate constant iscompared with the results of Tsang,14 Halstead et aZ.15 and Baronnet et aLz4 in fig. 4and it will be observed that the agreement is excellent.This is very reassuring sincethere have been unexplained discrepancies between rate constants obtained with th18 PYROLYSIS OF NEOPENTANEsingle-pulse shock tube in earlier work. The temperature range is too limited toprovide an accurate breakdown into the separate Arrhenius parameters and as RRKMcalculations show that the reaction must be close to its high pressure limit it is moresatisfactory to select an activation energy equal to the bond dissociation energy.The rate constant expression then becomes 3.3 x 10l6 exp( - 336 kJ mol-l/RT) s-l.As the rate constants for reactions (2) and (10) were constrained by the relationk l o = 0.5 k2, it is more satisfactory to discuss the results in terms of klo for whichother measurements are available.At 1200 K, Clark, Izod and Kistiakowsky ’’estimated a value of 2 x lo8 dm3 mol-1 s-l while Pacey and Purnell 26 obtained6 x lo7 dm3 mol-1 s-l. The present work gives a value of 4 x lo7 dm3 mol-’ s-l whichseems to support the lower of the two earlier measurements. The rate constantexpressions for k2 and klo seem entirely justified and add further weight to theobservation of non-Arrhenius behaviour for such reactions.The value for k14 is one-half that reported previously lo from measurements madeat lower temperatures and the agreement must be considered very satisfactory. It isdoubtful whether any rate constants reported for hydrogen atom addition to olefinscan justifiably be extrapolated to temperatures above 1000 K and there is considerableneed for additional experimentation in this area.The value obtained for the ratio kS2/k6 cannot be considered accurate as the productconcentrations are not particularly sensitive to this ratio.However there does seemto be a significant discrepancy between the present value and the value of 1.007 x lo6exp( - 173.7 kJ mol-l/RT) quoted previous1y.l This may be associated with the factthat, in the present system, C4H9 radicals are formed by H atom addition to olefinsso that both iso- and t-isomers occur, initially with excess energy. The reactionpressures also differed substantially between the two investigations.The value estimated for k19 must be regarded as suspect, first because it is a second-ary reaction involving one of the products, and secondly because other reactionssuch as (20) could be involved. The rates of the latter cannot be satisfactorily assessedbecause they are in competition with other hydrogen atom reactions to which thedecomposition is insensitive since they fall in class III.The authors wish to express their gratitude to the Hydrocarbon Research Panelof the Institute of Petroleum for the award of a studentship to one of them (K.0. W.).J. N. Bradley, Proc. Roy. SOC. A, 1974, 337, 199.J. N. Bradley and M. A. Frend, Trans. Faruhy Soc., 1971, 67, 1.J. N. Bradley and M. A. Frend, J. Phys. Chem., 1971,75,1492.J. N. Bradley and K. 0. West, J.C.S. Faruhy I, 1975, 71,967.C. G. Broyden, Mathematics of Computation, 1965, 19, 577 ; Computer J., 1969, 12,406.J. N. Bradley and K. 0. West, unpublished results.S. W. Benson and H. E. O”ea1, Kinetic Data on Gus Phase Unitnolecular Reactions (NationalBureau of Standards, NSRDS-NBS21, 1970).P. D. Pacey and J. H. Purnell, J.C.S. Furudzy I, 1972, 68, 1462.(Butterworth, London, 1972).’ K. H. Anderson and S. W. Bcnson, J. Chem. Phys., 1964, 40, 3747.lo J. A. Kerr and M. J. Parsonage, Evaluated Kinetic Data on Gas Phase Addition Reactionsl 1 A. F. Trotman-Dickenson and E. W. R. Steacie, J. Chern. Phys., 1951, 19, 169.l 2 B. de B. Darwent and R. Roberts, Disc. Faruhy Soc., 1953, 14,55.l 3 P. J. Boddy and E. W. R. Steacie, Canad. J. Chem., 1960,38, 1576.l4 W. Tsang, J. Chetn. Phys., 1966, 44, 4283.M. P. Halstead, R. S . Konar, D. A. Leathard, R. M. Marshall and J. H. Purnell, Proc. Roy.Soc. A, 1969,310,525.IG W. R. Trost and E. W. R. Steacie, J. Chem. Phys., 1948, 16, 361J . N. BRADLEY AND K. 0. WEST 19l7 A. F. Trotman-Dickenson and G. S. Milne, Tables of Bimolecular Gas Reactions (NationalBureau of Standards, NSRDS-NBS9, 1967).K. Schofield, Planet. Space Sci., 1967, 15,643.l9 R. R. Baidwin and A. Melvin, J. Chem. SOC., 1964,1785.2o K. 0. West, Ph.D. Thesis (University of Essex, 1975).21 V. V. Voevodsky and V. N. Kondratiev, Progr. Reaction Kinetics, 1961,1,41.22 R. S. Konar, R. M. Marshall and J. H. Purnell, Trans. Farahy Soc., 1968,64,405.23 R. S. Konar, R. M. Marshall and J. H. Purnell, Int. J. Chem. Kinetics, 1973, 5,1007.24 F. Baronnet, M. Dzierzynski, R. Martin and M. Niclause, Compr. rend. C, 1968, 267, 937.2 5 T. C. Clark, I. P. J. Izod and G. B. Kistiakowsky, J. Chem.Phys., 1971, 54, 1295.26 P. D. Pacey and J. H. Purnell, J.C.S. F4ruday I, 1972, 68,1462.(PAPER 5/196

ISSN:0300-9599    

DOI:10.1039/F19767200008

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Physicochemical Studies of Super-cooled LiquidsCyclic Carbonates and cc,P-Unsaturated AldehydesBY A. K. M. MASOOD AND R. A. PETHRICK*Department of Pure and Applied Chemistry, Thomas Graham Building,University of Strathclyde, Glasgow G1 1 XL, ScotlandANDF. L. SWINTONSchool of Physical Sciences, New University of Ulster,Coleraine, Northern IrelandReceived 3 1st January, 1975A range of measurements are reported on a series of substituted cyclic carbonates and a$-unsatur-ated aldehydes. The properties studied include the zero shear viscosity, thermal pressure coefficient,adiabatic compressibility, specific heat at constant pressure and the density. Certain of the liquidsstudied show a marked tendency to supercool and to exhibit pre-freezing phenomena. The magni-tude and temperature dependence of the properties studied are discussed in terms of cluster formationoccurring above the melting point.The source of the molecular interactions responsible for thecluster formation is discussed.Cluster formation or restriction of free isotropic rotation ’- has been suggestedas a prerequisite for the observation of pre-freezing phenomena in bulky covalentmolecular systems. The a priori prediction of the occurrence of pre-freezing pheno-mena requires a detailed understanding of the importance of the intermolecularpotential, the molecular anisotropy and of the chemical structure on local mobilityin the liquid state. The present study was undertaken in an attempt to identify theorigins of the observed variations of the physicochemical properties of a series ofsimple liquids.Previous acoustic attenuation studies of the cyclic carbonates andof the a,P-unsaturated aldehydes suggested that these systems exhibit very largetemperature coefficients of viscosity and a marked tendency to supercool.The cyclic carbonates form an ideal group for this type of study since they arerigid molecules of essentially similar size.6 Within the group studied the directionand magnitude of the dipole moment varies significantly. The a,a-unsaturated alde-hydes were studied for comparison purposes since they have a dipole of similarmagnitude but are flexible structures and possess significantly different rotationalvolumes. Studies of these two closely related groups of organic compounds allowsthe effects of size, flexibility and intramolecular potential to be identified.EXPERIMENTALFour cyclic carbonates were studied : Q-rnethyl-l,3-dioxolan-2-one, (propylene carbonate)obtained from B.D.H., 4-chloromethyl-l,3-dioxolan-2-one, (4-chloromethyl carbonate)obtained from Ralph N.Enianuel and Fluka A. G. (both samples were found to have identi-cal physical properties), 4-chIoro-1,3-dioxolan-2-one and 4,5-dichloro-1,3-dioxolan-2-oneobtained from Fluka. The three aldehydes, cinnamaldehyde, a-methylcinnamaldehydeand a-n-hexylcinnamaldehyde were obtained respectively from May and Baker, Kodak and2A . R. M. MASOOD, R . A . PETHRICK AND F . L . SWINTON 21K & K Laboratories. All samples were redistilled under reduced pressure and dried overmolecular sieves before use.In the case of 4-chloro- and 4,5-dichloro-l,3-dioxolan-2-onedecomposition is accompanied by darkening of the sample. Precautions were taken toavoid decomposition influencing the experimental observations. No detectable chemicalinstability was found in the remaining compounds studied. The physical properties, boilingpoints and refractive indices agree well with literature data.7*The following physical properties were measured on the cyclic carbonates and thea,B-unsaturated aldehydes.(i) Thermal expansion coefficient (ap) and density (p) were measured using a variety ofdilatometers calibrated with standard fluids and capable of being used below room tem-pera t ure .(ii) Thermal pressure coefficient at constant volume (yU) was obtained using an apparatuswhich is a modification of that originally described by Gee et aL9(iii) The adiabatic compressibility (&) was obtained from sound velocity measurementsas described elsewhere.' O(iv) The specific heat at constant pressure (C') was obtained using a Perkin Elmer DSCdifferential scanning calorimeter calibrated against indium and n-octane.l ' The highestinstrumental sensitivity and a scan rate of 8 K per minute were used. These data werecollected over a limited temperature range of 20 K per scan and are assumed to have anaccuracy of better than & 5 %. It should be appreciated, as will be discussed later, that thecurves obtained are sensitive to the precise thermal history of the sample.(v) The zero shear viscosity (Q) was obtained using a series of calibrated Ubbelohde sus-pended level viscometers (BS.IP.SL(S)71).12 All the liquids were passed through a sinterglass filter to trap solid particles.The temperature precision of all the experiments was better than +O.l K except in thedetermination of thermal pressure coefficient and the adiabatic compressibility where it waskO.003 K and *O.Ol K respectively.The pressure was measured in the thermal pressurecoefficient experiment to better than kO.0068 bar.RESULTS AND DISCUSSIONThe cyclic carbonates form an ideal system for the study of possible correlationsbetween the nature of molecular interactions and the observed bulk time volumeaveraged thermodynamic properties.indicated that slight puckering of the ring may occur in the case of the highly sub-stituted dichloro compound whilst the remainder possess slightly skewed planarstructures.The a,B-unsaturated aldehydes possess a flexible structure due to internalrotation of the carbonyl group and hence significantly different spatial extensionsand intermolecular interactions.Spectroscopic studies of the cyclic carbonatesVISCOSITY DATAThe cyclic carbonates and the unsaturated aldehydes were studied over a tempera-ture range from just above their melting points to approximately 353 K and theresults are shown in fig. 1. Most simple liquids exhibit linear plots of bog (q) againstreciprocal temperat~re,~ however exceptions to this ideal behaviour have been ob-served in the region of the melting point in certain systems.1 If these deviations werelarge the liquids showed a marked tendency to form glasses.Earlier studies of anumber of rather complex organic molecules such as the phenylbenzenes l5 and theterphenyls, indicated that the observation of so-called pre-freezing phenomena maybe associated with either cluster formation or with a restriction of the free isotropicrotatiofl of the molecules in the system. Both 4-methyl-l,3-dioxolan-2-one and4,s-dichloro- 1,3-dioxolan-2-0ne show only slight tendencies to supercool, exhibitalmost ideal Arrhenius behaviour and form glassy solids. The 4-~hloromethyl-l,3-dioxolan-2-one and 4-chloro- 1,3-dioxdan-2-0ne both show significant departun22 CYCLIC CARBONATES AND OI,~-UNSATURATED ALDEHYDESfrom ideal Arrhenius behaviour and possess a marked tendency to supercool.Bothliquids can be supercooled up to twenty degrees below their melting points and yetstill form apparently stable liquids. The three aldehydes show deviations from theideal Arrhenius behaviour similar to those observed in the cyclic carbonates.103 KITFIG. 1 .-Experimental viscosity against temperature relationships for the cyclic carbonates and theunsaturated aldehydes. A, 4-chloromethyl-l,3-dioxolan-2-one (m.p. 270 K) ; B, 4-chloro-1,3-dioxolan-2-one (m.p. 240 K) ; C, 4,5-dichloro-l,3-dioxolan-2-one (m.p. 273 K) ; D, 4-methyI-1,3-dioxolan-Zone (m.p. 232 K) ; E, a-n-hexyldnnamaldehyde (m.p. 282 K) ; F, cinnamaldehyde (m.p.275 K) ; G, cc-methyl cinnamaldehyde (m.p.265 K). Melting points indicated by arrows.The enhanced viscosity of the liquid as the melting point is approached may beconsidered in terms of the occurrence of cluster formation. If a volume fraction ofthe liquid consists of regions that move together like colloidal particles, the actualviscosity ve will be enhanced relative to that of the hypothetical supporting mono-molecular fluid tfm according to the equationwhere 9 is the volume fraction of clusters and the above equation can be shown tohold approximately provided that 9 does not exceed 0.3.l Applying this treatmentto the above systems and assuming that the viscosity of the monomolecular fluid canbe obtained by extrapolation of the linear high temperature region leads to fig.2.The plots are approximately linear as expected from the simple theory. If it is assumedthat cluster formation is controlled by a simple distribution equation then a plot ofy,/vm = 1+2.54+7$2 (1A . K . M. MASOOD, R. A . PETHRICK AND F . L . SWINTON 23log [( 1 - 4)/4] against 1 /T yields the mean enthalpy of formation for a cluster. Thedata obtained from this analysis are summarized in tabk 1. It is clear from the datathat the stabilization energy is larger in the cyclic carbonates than in the unsaturatedaldehydes. The errors in the determination of the enthalpies shown in table 1 arelarge although it would appear that it is a balance between the enthalpy and entropywhich is primarily responsible for cluster formation in these systems."t3.5 4.0 4.5103 KITFIG.2.-Plots of log 4 against reciprocal temperature. I$ is the volume fraction of clusters calcu-lated from eqn (1) (key as fig. 1).TABLE 1 .-EQUILIBRIUM DATA FOR CLUSTER FORMATION DERIVED FROM VISCOSITY MEASURE-MENTScompound4-chloromethyl-l,3-dioxolan-2-one4-methyl-l,3-dioxolan-2-one4-chloro-l,3 -dioxolan-2-one4,5-dichloro-l,3-dioxolan-2-onea-methylcinnamaldehydea-n-hexy lcinnamaldehy decinnamaldehydetemperaturerange/K278-303237-247243-293283-270293-270320-277305-270enthalp y I entropy /kJ mol-1 kJ mol-1 K-121.9 0.75420.2 0.84514.9 0.62712.7 0.5854.23 0.2807.03 0.3558.50 0.426THERMAL PRESSURE COEFFICIENTSThe thermal pressure coefficients were measured over a comparable temperaturerange to that used in the study of the viscosity for the cyclic carbonates and are shownin fig.3. These molecules behave abnormally in that their thermal pressure coeffi-cients are typically one and a half to two times larger than those found in comparableorganic liquids and also exhibit a tendency towards temperature independence astheir melting points are approached. Normal liquids exhibit thermal pressurecoefficients which fall continuously with increasing temperature.l The therma24 CYCLIC CARBONATES AND CL,#~-UNSATURATED ALDEHYDESpressure coefficient reflects the combined effects of " free " volume and the strengthof the intermolecular forces betwea the constituent molecules. The low values ofthe " compressibility " observed in the cyclic carbonates would suggest that themolecules are relatively closely packed but sufficiently disordered not to form solids.DENSITIESThe density data presented in table 2 indicate that 4-methyl-l,3-dioxolan-2-onehas a significantly higher molar volume than that of 4-chloro-l,3-dioxolan-2-one atcomparable temperatures.These molecules have similar " molecular " volumes andthe difference in their molar volumes indicates large differences in the magnitude ofthe " free " volume of these systems. A lowering in the free volume appears to beconsistent with the occurrence of deviations from ideal behaviour accompanying an12 6 0 3 0 0 3 4 0TIKFIG, 3.--y,,, the thermal pressure coefficients for the cyclic carbonates (key as fig. 1).increase in the cohesive energy.If it is assumed that deviations in the transportproperties are associated with the effects of free volume it may be expected that adiscontinuity in the thermal expansion coefficient similar to that observed in polymersin the vicinity of the glass transition temperature should be observed. No such dis-continuities were observed within the precision of these experiments. It may thcre-fore be suggested that the deviations from ideal behaviour must arise as a consequenceof enthalpic and entropic effects as much as from free volume limitations.ADIABATIC COMPRESSIBILITYContrary to the observations of the thermal pressure coefficients the adiabaticcompressibilities of the cyclic carbonates and unsaturated aldehydes shown in Q.4exhibit no significant deviations from apparently linear behaviour. Note, however,that those liquids with high values of the adiabatic compressibility also show the leasttendency to depart from ideal behaviourA . K. M, MASOOD, R. A . PETHRICK AND F . L . SWINTON 25SPECISIC HEAT AT CONSTANT PRESSUREThe specific heat at constant pressure for the cyclic carbonates was measured overan extended temperature range covering the region of interest in the viscosity studies,fig. 5. The plots obtained are similar to those previously reported for terphenyl l7TABLE 2.-DENSITIES OF CYCLIC CARBONATES AND UNSATURATED ALDEHYDESp/g ~ r n - ~ = a+b(T/K-273.2)a4-methyl-l , 3-dioxdan-2-one 1.241 154-chloromethyl- 1,3-dioxolan-Z-one 1.482 034,5-dichloro-l,3-dioxolan-2~one 1.619 16Cchloro-1,3-dioxolan-2-one 1.552 34cinnamaldehyde 1,089 5a-me t hylcinnamaldeh yde 1.058 2a-n-hexylcinnamaldehyde 1.049 5b x 1030.621 70.955 81.099 71.400 10.8610.877 50.860and the other glass-forming solids.The specific heat plots shown in fig. 5 representthe average of a number of measurements. In practice the exact curve is a functionof the thermal history of the sample. In the case of the study on terphenyl l7 it waspossible to obtain the specific heat data for a crystal of the material. In the presentcase it proved impossible to seed a crystal and the corresponding data are not available.263 2 83 3 0 3 323T KFIG. 4.-&, the adiabatic compressibility (key as fig. 1).It was found that for the glassy material the general shape of the curve changed littlewith thermal cycling and the uncertainty in the data reported is approximately ;fi: 5 %.Comparison of the traces with the previous thermodynamic observations Suggeststhat a correlation exists between the upturn at the high temperature end of the plateauregion and the onset of the ideal behaviour in these systems.A detailed investigationof the traces indicated that certain of the molecules possess exo- and endo-thermi26 CYCLIC CARBONATES AND C@UNSATURATED ALDEHYDESproperties which are modified by thermal cycling. No melting transition wasobserved in 4-methyl-l,3-dioxolan-2-one ; however, 4,5-dichloro- 1,3-dioxolan-2-0neshowed semblances of such a process at 269 K. In the latter system the amplitudeof the transition was very much a function of the thermal history of the sample.Transitions were observed with variable amplitude in both 4-chloro- and 4-chloro-methyl-l,3-dioxolan-2-one at respectively 264 and 285 K.It is clear that the exo-therms are not associated with “ melting ” transitions which should occur 10-20 Klower than these temperatures and it is more reasonable to suggest that these observa-tions may in some way be attributed to the onset of ‘‘ free ” isotropic rotation of thewhole molecule. In all cases the magnitude of the transitions were small and difficultto quantify and have therefore not been included in fig. 5. A correlation betweenthe observed specific heat and free rotation has been proposed for anisotropic mole-cules and is compatible with the above data.2* The glass transition temperatureshave not been satisfactorily established for these materials but may be expected tocorrelate with low temperature change in slope of the specific heat curve.The sen-sitivity of the curves and transitions to the thermal history of the sample would suggestthat a free rotational model should be favoured but does not preclude these effectsarising from the break-up of local structure in the 1iq~ids.l~25T/KFIG. 5.-Cp, the heat capacity at constant pressure (key as fig. 1).CALCULATION OF THE PAIR-WISE INTERACTION ENERGYConsideration of the basic structures of the cyclic carbonates suggests that signifi-cant dipolar interactions may occur via the carbonyl group.Calculations wereperformed using van der Waals and dipolar interactions, the former being calculatedon the basis of standard Lennard-Jones 6-12 potentials as described elsewhere.2oThe pair of molecules were assumed to line-up with their carbonyl groups parallelbut in opposite directions. In this configuration the planes of the rings will beparallel and the separation between the rings is taken as a variable. The carbonyldipole moment is assumed to have a value of 10.7 x C m and the van der WaalA . K . M. MASOOD, R . A . PETHRICK AND F . L . SWINTON 27interactions up to 600 pm are considered to be significant. The interaction potentialwas calculated at a series of separations and minimum energy condition obtained byan iterative process. The minimum in the potential (fig.6 ) occurs at approximately320 pm and has a stabilization energy of 4.57 kJ mol-I. It is apparent from this cal-culation that the carbonyl interactions do in fact form a source of significant inter-action which may be considered as the driving force for the formation of clusters inthe liquid but do not totally explain the observed effects. A similar dipolar inter-action may be expected to occur between the carbonyl groups of the unsaturatedaldehydes.32I- 2- 3- 4\ 300 400 500 600FIG. 6.-Potential energy diagram for the pair-wise interaction of cyclic carbonate rings.CONCLUSIONThe measurements reported on the cyclic carbonates and unsaturated aldehydessuggest that supercooling is associated with the occurrence of a large configurationalentropy l9 accompanied by a significant enthalpy of association arising from pairwiseintermolecular interactions and often a limitation on the free volume of the system.The cyclic carbonates exhibit deviations from ideal behaviour as a result of cluster-ing favoured by dipolar interactions involving the ring carbonyl groups.This cluster-ing may involve a significant number of molecules forming dynamic cylindrical struc-tures. The non-ideal nature of the clusters which may be associated with the aniso-tropy of the molecules adds to the configurational entropy of the liquids which inturn leads to an increase in the viscosity. It is perhaps significant that the occurrenceof a dipole component perpendicular to the carbonate ring assists the cluster formationand leads to the marked deviations from ideal behaviour.The perpendicular com-ponent will assist the alignment of the rings and stabilise the pairwise interactionfurther. It is clear that a more detailed understanding of the mechanism responsiblefor the observed premelting phenomena requires characterization of the detailedmotion of the constituent molecules28In the unsaturated aldehydes the pendant group appears to produce cooperativeinteractions and leads to the observed deviations from ideality. It is also clear thatin the latter series the strengths of the interactions are lower than in the cyclic carbon-ates (table 1) and it must be assumed that configurational effects possibly involvingthe flexible end-groups play an important role in the observed behaviour.CYCLIC CARBONATES AND CC,/?-UNSATURATED ALDEHYDESA.R. Ubbelohde, Melting and Crystal Structure (Clarendon, Oxford, 1965).D. B. Davis and A. J. Matheson, Disc. Furuday Soc., 1967, 43, 216,D. B. Davis and A. J. Matheson, Trans. Fnraday Sue., 1967, 63, 596.R. A. Pethrick, E. Wyn-Jones, P. C. Harnblin and R. E. M. White, J. Chem. Soc. A , 1969,1852.C. J. Brown, Acta Crysi., 1954,7, 92.N. F. Grishchenko and V. N. Pokorskii, Nefteppererab Nefiekhim., 1966, 33 (Chem. Abs. 1966,54960~).P. C. Hamblin, Thesis (University of London, 1968).G. Allen, G. Gee, D. Mangaraj, D. Sims and G. J. Wilson, Polymer, 1960, 1,467.Perkin Elmer manual for DSC-1.A. R. Ubbelohde, J. Inst. Petroleum, 1973, 23, 427.’ R. A. Pethrick and E. Wyn-Jones, Trans. Faraday Soc., 1970, 66, 2483.lo R. A. Pethrick, J. Phys. E., 1972, 5, 571.I 3 A. D. Wilson and R. A. Pethrick, Spectruchim. Acta, 1974,30A, 1073.l4 W. T. Laughlin and D. R. Uhlrnann, J. Phys. Cheni., 1972,76,2317.l6 J. N. Andrew and A. R. Ubbelohde, Proc. Roy. SOC. A , 1955, 228, 435 ; R. J. Greet and D.l7 S. S. Chang and A. B. Bestul, J. Chem. Phys., 1972, 56, 503.l9 J. F. Martin, in Chemical Thermodyizainics (Spec. Periodical Rep., Chem. SOC., London, 1973),2o R. L. Cullough and P. E. McMahon, Trans. Faruday SOC., 1964, 60, 2089.A. C. Ling and J. E. Willard, J. Phys. Chem., 1968, 72, 1918.Turnbull, J. Chern. Phys., 1967, 46, 1243.J. F. Counsell, E. B. Lees and J. F. Martin, J. Chem. SOC. A, 1968, 1819.vol. 1, p. 156.(PAPER 5/210

ISSN:0300-9599    

DOI:10.1039/F19767200020

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Molecular Theory of Adsorption in Pore SpacesPart 2.-Thermodynamic and Molecular Lattice Model Descriptionsof Capillary CondensationBY DAVID NICHOLSONPhysical Chemistry Laboratories, Department of Chemistry,Imperial College, London SW7 2AYReceived 3rd March, 1975A new thermodynamic analysis, which avoids some of the limitations of previous treatments,is made of the process of adsorption and filling in cylinders. Expressions for the surface tensionare derived for a molecular lattice model and relationships with the Gibbs and Frenkel, Halsey,Hill equation examined. The special nature of the latter equation is discussed and compared withthe lattice model. Results for a nitrogen-like system at 77.4 K are compared with predictions fromvarious thermodynamic equations.It is found that aq adsorption cgrrectim to the Cohan equationis necessary for the best agreement but that none of the thermodynamic expressions tested were ableto predict the molecular results.There is considerable uncertainty concerning the part played by adsorption forcesin capillary condensation in mesopores. Nevertheless extensive use is made of thisphenomenon in pore size distribution analysis where a simplified picture of isolatedcylinders is often ad0pted.l A common procedure is to employ either the Kelvinequation for desorption or the Cohan equation for adsorption, corrected for adsorbatethickness. Broekhoff and de Boer showed that the Cohan equation, which appliesto a film of adsorbate on the cylinder wall, does not correspond to thermodynamicallystable conditions and they introduced an additional term which restores this stabilityand which depends on the adsorbent field.The derivation of this corrected equationhas been criticised however and the correction has been largely ignored in inakingpore size distribution analyses.Apart from the question of the rale played by the adsorbent field, there is additionaluncertainty because the bulk fluid approximations used in thermodynamic treatmentsmay not be applicable to systems of small radius or to thin films of adsorbate. Theselimitations are expected to apply outside the micropore regime, i.e., even whenmesopore behaviour (adsorption plus capillary condensation) is found.An evaluation of the problem is possible in terms of the lattice model developedin Part 1 and enables some insight to be gained into the process of adsorption incylinders.In this paper calculations based on the lattice model are compared withthe thermodynamic approach using as a reference point the relative pressure at whichcondensation occurs.EQUATIONS BASER ON THERMODYNAMICSPLANAR ADSORBENTConsider a planar adsorbent of area A in the presence of X molecules of adsorbatecontained in a system of volume V (bounded by the adsorbent as one face), entropy S,230 DESCRIPTIONS OF CAPILLARY CONDENSATIONtemperature T and chemical potential p. The total differential of the internal energyU isdU = TdS-p dV+y dA+p dX. (1)The adsorbent is assumed to be unperturbed by the adsorbate. y can be definedin terms of the diagonal components of the pressure tensor bywhere the z axis is perpendicular to the surface and z = h is in the homogeneous gasphase at a great distance from the adsorbent surface.The tangential component ofthe pressure tensor pT is equal to pxx = pry and the normal component p equals pzz.For the adsorptive interface at T, pzz = p o , the saturation vapour pressure, and ybecomesS hY o = 1 [Po-P;(z)l dz. (3)LR = U+pV-TS-yA (4)(5)- hA free energy C2 can be defined byand the Maxwell relations derived from (4) lead to a total differential for the chemicalpotentialwhere the bars denote partial derivatives with respect to X at constant T, p , y. At alarge distance from the surface in the homogeneous gas phasedp = - S dT+ Vdp-A dydp = - S , dT+ V, dp.(6)Eqn (5) at constant temperature is the Gibbs isothermAd?- Vdp = -dp. (7)A more familiar form of this equation is obtained by introducing (6) with v 4 7,and an ideal gas phase assumption to giveA dy = k,Td lnp. (8)WPIPo) = -Pf(t,), (9)A dy = -flf’(t,) dt,. (10)The adsorption isotherm can be expressed in terms of the adsorbate thickness onthe plane surface t, asin whicb p/po is the relative pressure, p = l / k J and tp and the function f will bediscussed more .fully below. Eqn (9) with (8) givesThe spreading pressure # ( X ) can be found from (7), (8) or (10) by integratingbetween limits which correspond to X = 0 and X . Alternatively integration of (8)from X to X = oc) at p = po givesBA(y -yb) = pv@ -PO) - 1 In (pko)? (1 1)where the ideal gas condition has been used with eqn (6), A = U / d X = A/X andAh = V.In eqn (1 1) yb applies to the solid covered with a Duplex film of adsorbatemany molecular diameters thick andwith ysL the interfacial tension between adsorbent and adsorbate.Y b = YO+YSL (12D. NICHOLSON 31ANNULAR ADSORBATE IN A CYLINDERHere the adsorbate density decreases radially towards the centre of the cylinder,the pressure in the radial direction is a function of radius r. For a bulk fluidapproximation the pressure can be divided into two parts :dense phase p(r) = ps = constant ; r (rp- t )rarefied phase p(r) = pa = constant ; r < (rp - t ) (1 3)where rp is the radius of the cylinder and t the thickness of the adsorbate on thecylinder walls; as will be seen below t can be determined in more than one way.Eqn (1) is nowwhere R1, R2 are principal radii of curvature and C1, C2 the conjugate potentials;for an annular fluid R1 = - r and C2 dR2 = 0.Eqn (14) leads toand y is now dependent both on position and curvature of the interface. It is usualto choose y to have its minimum value with respect to r which leads to the Laplaceequation; in the present context this iswhere ym is not necessarily identified with y defined for the plane surface. The negativesign appears in (16) because the area of the cc-b interface decreases with increasingvolume.The difference between the chemical potential of the adsorbate film at ps and thesame phase with a plane surface under saturated vapour pressure ps is expressed bythe conditionIf phase a is an ideal gas and vp is constant for an incompressible dense phase,eqn (17) givesd U = TdS-pSdVg-p,dV,+YdA+Cl dRi+CzdR2+pd-Y (14)dp = -S dT+ Vj dpp+ V, dpa-A dy-C dr (1 5)(PB -Pa) = - ~ m / ( r p - t), (16)Pa) - PO) = P ~ T , PP) - P~(T, PO).(17)where the final equality is obtained by introducing eqn (1 6).Eqn (1 8) would be the Kelvin equation for the adsorbate film in a cylinder, if thefirst term on the right-hand side was neglected. Melrose has given a detaileddiscussion of the importance of this term (usually small) and of the consequencesof neglecting the compressibility of P (which can be significant).The foregoing discussion emphasises the fact that both ym and t involve someuncertainties in the present context.Even if the curvature dependence of ym isneglected it must be expected to vary with the thickness according to eqn (8)-(10).For example the left-hand side of eqn (9) can be integrated between y& and ymgivingand A for a film of thickness t in the cylinder is given byaA at av, 32 DESCRIPTIONS OF CAPILLARY CONDENSATIONEqn (19) with (20) giveswhich, after substitution in (1 8) and rearrangement givesTHE SLAB THEORY OR FHH EQUATIOKThe Frenkel, Halsey, Hill (FHH) equation can be writtenIn(p/pO) = -KF/lS,in which KF is a positive constant. The equation can be derived both from thermo-dynamic reasoning and from a perturbation theory * to give a value of s = 3.0.Several experimental investigations have indicated that s is less than 3 for realadsorbents and this diminution is attributed to surface heterogeneity effects.A rnodi-fied form of eqn (23), obtained by fitting experimental isotherm data, has been usedby de Boer and co-workers.2The FHH equation is of special interest here because the adsorbate is treated asa slab of fluid in the field of the adsorbent. This description is more likely to becorrect for thick films of adsorbate (t > 2 layers) and accords rather well with theassumptions leading to the derivation of eqn (22). In particular the value of y foran infinitely thick film will simply be yo and eqn (22) becomesThis equation would be the same as that derived by Broekhoff and de Boer if thesecond term on the left-hand side was neglected and the second term on the right-handside was replaced by their t-curve.The equation also carries the implication that onlythe adsorbate/vapour interface is relevant to capillary condensation.When the second terms on both sides of eqn (24) are neglected the remainingexpression is the Cohan equation.To conclude this section a derivation of the FHH equation from the lattice modelof Part 1 is given. A comparison with calculated isotherms is made in the Resultsand Discussion section.In the slab theory the adsorbate consists of iz layers with fractional occupationequal to that of the reference state. When this condition is imposed on eqn (17)of Part 1 the entropy term and adsorbate interaction term vanish leavingIn (PlPo) -C E mi JT- (25)The adsorbent-adsorbate interaction function mi = - I/$ for a planar continuumadsorbent and inverse sixth power attraction between individual atoms.The distancezi of the ith layer from the surface is measured in units of the adsorbate moleculardiameter ro and to a close appr~ximation,~ zi = i-3, thus (25) isThe number of layers n is related to the thickness t, by 6’a = t, where 6’ is the(= 0,816 5 for a cubic close packed lattice). thickness of each layer in ro unitD. NICHOLSON 33After carrying out the summation in eqn (26), rearranging and substituting for n theslab theory result is obtained :The constant 4.35 in eqn (27) is for a cubic close packed lattice and E is definedas 2E(Zo)/3kB where E(zo) is the potential energy minimum.MOLECULAR EQUATIONS BASED ON THE LATTICE MODELPLANAR SYSTEMSIn the lattice model the surface tension can be derived by several routes; onewhich is convenient and direct is to integrate eqn (1) to givewhere Z is the grand partition function,and for the most probable occupation set chosen from the sum over all occupationswhere Q is the canonical partition function given by eqn (9) and (1 1) of Part 1 andj?p is given by eqn (12) of Part 1.When these equations are substituted into (30)the result for a planar lattice of k layers isP(U-TS-pN) = P(-pV-yA) = -In= (28)/ M y = -lnZ+flpV (29)I n 3 = lnQ+XPp (30)where M is the number of sites in a layer ; @& is the adsorbate interaction term andE* is the well depth of the 6-12 interaction.The equation of state for the reference fluid is given by eqn (18) of Part 1 whichfor a lattice with k layers can be writtenwhere 8 is the fractional occupation of the lattice for a bulk homogeneous referencestate at (po,T).For the adsorbate a similar expression describes the gas phase at a large distancefrom the surface, in this case p o is replaced by p and 6 by eg, the fractional occupationof the gas phase at (p,T).In eqn (32) the term a is given byppo V = Mk[ - ln (1 - 0) + 36’a-j (32)and by expanding the interaction term in (31) it can be shown that this becomes #12awhen = 8, = 8 and k is large compared with the range of the interaction. Anexpression for yo is now obtained from (31) and (32) as a sum of contributions fromeach layer.where 6 is the area per m01ecule.~ A comparison with eqn (3) shows that for thelattice model Asp+(z) dz is replaced by the sum over i in eqn (31).Eqn (31)can therefore be interpreted as a sum of pV contributions, one from each layer.When Og replaces 8 and (0,’) for adsorbate in contact with adsorbent is used,eqn (33) gives y.1-34 DESCRIPTIONS OF CAPILLARY CONDENSATIONCYLINDRICAL SYSTEMSFor adsorbate in a cylinder eqn (31) becomeswhere the (Oil is now a solution for the lattice model equations in cylindrical geo-r n e t r ~ . ~ The external gas phase equation of state for a fractional occupation eg isand V here is the cylinder volume. Eqn (34) and (35) can be substituted in (29) togive a lattice model equation for pAy, (where the subscript c emphasises that theresult is for cylindrical geometry).Clearly the product Aye is invariant to placementof the interface for a given cylinder.Some further insight into the link between the thermodynamic and molecularequations can be gained by writing pa, ps from eqn (13) as the mean values,P/? = P(l)pdr/Sm r,-2 r dr; pa = J::ot p(r)r dr/S?' 0 r dr. (36)It can then be shown, after some algebraic manipulation, that(37)2(rp - t>ri(Pa - Pi)t k2 Ym = c l < i < kwhere p i , given by flZpiV = In Z, can be found from (34). Although eqn (37) canbe considered as the cylindrical analogue of eqn (3) it cannot be evaluated withoutassigning values to t and pa. The latter is usually identified with the external gasphase pressure, but eqn (36) shows that pQ would equal this pressure only when thecylinder of radius rp- t lies totally within a region where the adsorbent field is zero.THICKNESS OF THE ADSORBATE LAYERSeveral definitions of thickness of the adsorbate layer are possible; three, whichare of particular interest, are considered here.A natural definition of thickness can be given in terms of the Gibbs excess withrespect to the homogeneous gas and dense phases pg, pz at (p,T).In generalised formthe defining equation iswhich can be solved for V(t) the volume enclosed by a surface at thickness t. Inplanar geometry eqn (38) giveswhere GM = E(Oi - Og) is the number of filled layers in the surface excess. It is worthnoting that neither (38) nor (39) implies that the adsorbate necessarily has the densitypz at any point.t, = sw,/(e-eg) (39)For an adsorbate in a cylinder eqn (38) can be solved to givet,, = rp 1- - [ (BgT;)+]where 0' is the fractional filling of the cylinder = XCxi/CMi for the lattice model.If it is assumed that an adsorbed rnonolayer fills to the same fraction 0 as thD. NICHOLSON 35I.C30.90.-(2.8s-0.70C.6 0dense reference state then eqn (39) defines the number of such layers in the surfaceexcess.A formal thickness for the adsorbate can be defined in an analogous way.An adsorbate thickness can also be found 2 * lo by solving eqn (24) and in particularthe value at which this equation predicts filling can be found from the conditiona(p/po)/at = 0 ; some further detail is given below, the result of this calculation givesa value of t = tE.--RESULTS AND DISCUSSIONIn this section the properties of eqn (24) are compared with results for the mole-cular theory based on the lattice model.Isotherms were calculated for spherical nitrogen-like molecules using the para-meters; r0 = 4.15, E* = 95 K, E = 750 K, T = 77.4 K and the range of radii2.0 < rp < 33.0 in ro units.The isotherms are similar to those obtained for Ar at80 K except that step structure is very much less evident. There is a two phaseco-existence region for Y, > 4.0. A plot of (p/p0)*, the relative pressure at which thephase transition ocurs, against rp is shown in fig. 1.*040 t G2.30 - I 0 . 2 dc\. I 00 -4- - .w.01 I I I IC 10 2 0 3 0rPFIG.1.-Relative prcssure at condenstion as a function of cylinder radius for a nitrogen-like adsor-bate at 77.4 I<.An isotherm for the same system with a plane surface was calculated and the dataused to evaluate y from the appropriate version of eqn (33) as explained in 3.1.A calculation of Byo for the reference fluid was also made. /?y is shown as a functionof p/po in fig. 2. It may seem surprising at first sight that y < 0, but analysis ofeqn (33) and the calculated (&> shows that a large negative contribution comes fromthe first one or two layers where Oi > (1 - Og). This means that these layers aredenser than the bulk reference fluid wouid be at (p,T) with a consequently largenegative contribution from the logarithmic (i.e., entropy) term in eqn (33).Th36 DESCRIPTIONS OF CAPILLARY CONDENSATIONmagnitude of this term very probably highlights the limitations of the model, never-theless the abnormally high density of the layers near to the wall is a realistic feature.It is clear from eqn (33) that non-zero contributions to y or yo can only come fromlayers in which 13, is not equal to a homogeneous bulk phase value. For the referencestate, zero contributions occur when Oi = I3 or 0; in the liquid or gas-like phases eitherside of the interface. For an adsorbate phase, contributions to y fall to zero at avalue of i which increases with p and for which Oi + Og. However when p is veryclose to p o a second region of zero contributions to y appears which separates thefirst few layers with Qi > 8, due to proximity of the adsorbent, from a region withthe structure of the reference state interface. This is illustrated in fig.3.15.0 --13.01 ' 4*0r(PIPO)FIG. 2.-Surface energy as a function of relative pressure for adsorption at a plane surface.iFIG. 3.-Adsorbate density profile over 40 layers at p/po = 1.00.In fig. 4, eqn (23) is tested for the plane surface results from the lattice model; anexcellent fit was found for 1.8 < OM < 6.0 but the value of s (= 2.87) was less than 3.A similar result was obtained for Ar-like molecules at 80 K with s = 2.88. In viewof the approximations necessary to derive eqn (27) it is not surprising that s # 3 butit is of interest that the result is not much higher than that found for experimentD.NICHOLSON 37isotherms and that surface heterogeneity effects do not occur here. The value ofthe constant KF (= 15.3) was likewise much lower than would be predicted fromeqn (27). An expression for y from eqn (23) can be found by substitution in eqn (8)and integration to givewhich predicts y > yo and positive. The apparent contradiction between this resultand y calculated for the lattice model (fig. 2) can be resolved by the conjecture thatan isotherm of the form of eqn (23) accounts only for the field effect on a film ofadsorbate caused by replacing the adsorbate fluid by adsorbent, but includes noallowance for the entropy change. This model certainly underlies all derivations ofeqn (27) and must be presumed to extend to the general empirical form (23).It might, , ,\ - 3.00 . 2 0.4 0 . 6 0 . 8 1.0 1.2 1.4 1.6 1.8la OMFIG. 4.-Test of the FHH equation for nitrogen-like adsorbate at 77.4 K.also be conjectured that eqn (41) is only relevant to the adsorbate/vapour interface[cf. eqn (12)] and is thus particularly suited to representf(t) as in eqn (24). At thesame time the foregoing discussion of y makes it clear that its components in eqn (12)are not distinguishable at p/po < 1 .O which adds to the difficulties of finding a reliablethermodynamic equation to describe adsorption in mesopores.The table compares lattice model calculations for the left-hand side of eqn (24)with various estimates based on the right-hand side38 DESCRIPTIONS OF CAPILLARY CONDENSATIONThe following parameters were used for these calculations : vb was equated withthe molar volume of the dense reference state (poO0)-l where po, the number densityof the filled C.C.P.lattice = J2 and 8 was found to be 0.949 6 for the energy para-meters &* = 95 K, T = 77.4 K. As in Part 1 the reduced temperature was used inthe calculations. From the equation of state, eqn (31), flVBpo = 0.045. The con-stant was found to be 0.508 from eqn (33) (about half the experimental valuefor N2 at 77.4 K). Together with the FHH isotherm parameters given in the preced-ing paragraph these results, inserted into eqn (24), giveln(p/po) + 0.045(1- p/po) = - [;;::) - +l:.:'i] -TABLE 1 .-THERMODYNAMIC AND LATTICE MODEL PREDICTIONS FOR THE RELATIVE PRESSURE OFCONDENSATION IN CYLINDERS'D4.134.955.766.587.398.219.851 1.4813.1114.7516.3819.6422.9126.1829.4432.71(A)W P b e ) '3- 0.045-p/pO)* tGC-1.270 2.22-0.911 2.59-0.715 2.89-0.528 3.30-0.467 3.39-0.385 3.59-0.299 4.00-0.219 4.4-0.170 4.7-0.145 4.9-0.133 5.2-0.103 5.6-0.087 6.0-0.075 6.3-0.053 6.6-0.043 6.8tE2.763.163.543.904.244.575.195.776.326.837.338.259.119.9210.6711.40(B)-0.SOSl(rp- t c 3- 0.266-0.215- 0.177-0.155-0.127-0.110- 0.087- 0.072- 0.060 - 0.052 - 0.045- 0.037- 0.030- 0.026- 0.022- 0.020(C)epn (40)wlth t = tGC- 0.752- 0.528- 0.405- 0.31 1- 0.271- 0.233-0.177-0.140-0.117-0.102- 0.087- 0.071- 0.065- 0.054-0.043-0.040(D)epn (40)- 0.63 1- 0.460-0.356- 0.286- 0.237- 0.201-0.152- 0.120- 0.099- 0.084- 0.072- 0.056 - 0.046- 0.038- 0.033- 0.040with t = tE (A)/@) (A)/(C) (A)/@)4.77 1.69 2.014.24 1.73 1.984.04 1.77 2.003.41 1.70 1.853.68 1.72 1.973.51 1.65 1.923.44 1.69 1.973.06 1.56 1.832.81 1.45 1.722.80 1.45 1.742.96 1.53 1.852.81 1.45 1.842.90 1.34 1.922.94 1.38 1.982.40 1.28 1.632.20 1.10 15.2Values of tE were found by iterative solution of the equation obtained from thecondition 8(p/po)/8t = 0; lo which, froni eqn (42) givesA zeroth approximation was obtained from the solution lo for s = 3 which with theparameters used here isDirect iteration of (43) is slow but is accelerated by setting t(') = +(t(f-1)+P-2)) andis easily performed on a modern desk calculating machine.The Gibbs thickness defined by eqn (40) was estimated at the transition value(p/po)* from the calculated isotherms, the uncertainty in each value can be quite largeas indicated in fig.5 ; the tabulated values were estimated from the best line as drawnin the figure.The ability of the thermodynamic equations (24) or (42) to predict the molecularlattice model results is tested by calculating ratios of the right-hand side to the left-hand side of eqn (42) ; the latter [(A) in the table] having been obtained from calculatedisothcrms. The poorest and most variable prediction is that given by the Cohan(43)(44)t(i+l) = 2.345 (r, - t(1))0-517,t ( O ) = 2.59 [(1+0.769 rp)'- 11I>.NICHOLSON 39equation (€3 in the table). The correction for adsorption makes a marked improve-ment with t = tcc (C) giving a slightly better result than t = tE (D). In all cases thereis a slight improvement towards higher rp but this may be only apparent due to un-certainties in (p/po)*.The results summarised in the last three columns of the table are consistent withthe view that an equation of the form of (24) is more suitable for the description ofadsorption in a cylinder than is the uncorrected Cohan equation. It has been arguedelsewhere lo that an analysis of adsorption branch data should be preferable todesorption branch analysis in networks because of freedom from the pore blocking01 t I I I 1 J0 10 20 3 0rPFIG. 5 . 4 i b b s thickness of the adsorbate prior to condensation as a function of pore radius.effects which contribute to hysteresis. The present work furthermore indicates thatit is unlikely that any thermodynamically based treatment can properly represent theadsorption process in the mesopore size range. However the lattice model itselfinvolves too much approximation to allow any quantitative as opposed to qualitativereliance to be placed on the results presented here.We thank Dr. J. H. Petropoulos for discussions, in particular of the thermodynamicsection of this work.S. J. Grcgg and K. S. W. Sing, Aclsorption, Swfme Area and Porosity (Academic Press, London,1967).J. C. P. Broekhoff and J. H. de Boer, J. Catalysis, 1967, 9, 8.J. C. Melrose, J. Colloid Interface Sci., 1972, 38, 312.D. Nicholson, J.C.S. Fwaday I, 1975,71,238.F. C. Goodrich, in Swface and Colloid Science, ed. E. Matijevic (Wiley, New York, 1971),vol. 1.D. H. Everett, Soc. Chem. I d . Monograph No. 25,1967, 157.J. C. Melrose, A.Z.Ch.E.J., 1966, 12,986.K. S. W. Sing in Colloid Science (Spec. Periodical Rep., Chemical Society, London, 1973),vol. 1.a W. A. Steele, The Interaction of Gases with Solid Surfaces (Pergamon, Oxford, 1974).lo D. Nicholson, Trans. Farahy SOC., 1968,64,3416

ISSN:0300-9599    

DOI:10.1039/F19767200029

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Adsorption and Surface Reactivity of Metalsby Secondary Ion Mass SpectrometryPart 1.-Adsorption of Carbon Monoxide on Nickel and CopperBY MICHAEL BARBER, JOHN c. VICKERMAN" AND JOHN WOLSTENHOLMEDepartment of Chemistry, The University of Manchester Institute of Science andTechnology, Sackville Street, Manchester M60 1 QDReceived 10th March, 1975The adsorption of carbon monoxide on polycrystalline nickel and copper has been studied bysecondary ion mass spectrometry (SIMS), in the temperature range 77-390 K. The results indicatethat carbon monoxide is adsorbed in both a linear and a bridged form on nickel in the range 77-370 Kbut only in a bridged form at temperatures above this. For copper only a linear structure wasobserved at 77 K and only a bridged structure at 295 K.On both metals there is a build up ofcarbon on the surface at 390 K. These results are discussed in terms of those obtained from othertechniques.The adsorption of carbon monoxide on nickel and copper has been studied bymany different techniques. A review of the more recent literature reveals that areasonably consistent picture is emerging.NICKELThe picture here appears to be that carbon monoxide is adsorbed in three distinctphases which, in the terminology of thermal desorption studies, are called PI, P2and y. This agrees with the results of LEED studies.2* These indicate that threephases are formed but that these phases do not co-exist on the surface and that phasechanges occur at definite coverages. 1.r. experiments give rise to two bands whencarried out at temperatures at which the most weakly adsorbed, y, phase is expectedto be present.The high frequency band is assigned to a linear Ni-C-0 structureand the band at lower frequencies to a bridged Ni2C0 structure.There has been some argument in the literature as to whether the adsorption ismolecular or dissociative. One LEED study suggests that molecular carbonmonoxide is adsorbed on top of a layer formed by dissociative adsorption of carbonmonoxide. A recent UPS and XPS study,6 however, indicates that, at room tempera-ture, the adsorption of carbon monoxide is entirely in the molecular form and onlyprolonged heating of the metal in the presence of carbon monoxide causes dissociationto occur.COPPERThe literature is quite clear that there are two types of adsorption of carbonmonoxide on copper. The first type of adsorption causes an increase in the intensityof the single i.r.band with coverage and the second type of adsorption causes nochange in its intensity but the band shifts to higher frequencies as coverage progresses.The change-over in the i.r. spectrum coincides with a maximum in the surface potential4M. BARBER, J . C. VICKERMAN AND J . WOLSTENHOLME 41and a phase change on the surface, as observed by LEED.*'l0 The second, moreweakly bound phase can be formed only at low temperatures and is completelydesorbed at 195K. The more strongly bound species is desorbed at room tem-perature.SECONDARY ION MASS SPECTROMETRYSince SIMS, as applied to surface chemistry, is a relatively new technique we haveattempted here to investigate its scope and limitations by applying it to well-studiedsystems.Its limitations could be that the primary ions cause fragmentation of thesurface species or cause changes in the metal surface which would alter the mode ofadsorption of the gas.It is believed that neither of these phenomena occur and, further, that SIMS cannot only confirm a suggested model but also clarify and, to a certain extent, amplifysuch a model.It is the aim of this paper to show how far this is true by comparing our resultswith the overall picture of CO adsorption which emerges from the data outlined above.Exact agreement with the detail of these results would not be expected, since it is verydifiicult to reproduce precisely the conditions under which these experiments wereperformed.EXPERIMENTALThe SIMS apparatus was constructed by Vacuum Generators Ltd. and was similar indesign to that described by Benningh0ven.l' The instrument has been described in detailelsewhere.Briefly, the instrument consists of two, separately pumped chambers, a preparationchamber and an analysis chamber connected by a gate valve.The sample is cleaned in thepreparation chamber by argon ion etching using 6 kV argon ions from a V.G. AG2 ion gunat a current density of about 100pA cm-2. After cleaning, the metal is transported to theanalysis vessel by means of a u.h.v. bellows system.In the analysis chamber the primary ions are incident on the sample at an angle of 70"from the normal with an energy of 3 kV and a current density of 10-9-10-10 A ern-'.The base pressure attainable in both chambers after baking was about 2x 10-l' Torrbut the pressure in the analysis chamber rose to lo-* Torr due to argon entering the chambervia the primary ion gun when in operation.The argon for both the primary ion source and the AG2 gun was purified by passing itthrough a trap containing molecular sieve (zeolite) to remove traces of hydrocarbon. Toremove water the trap was cooled in a mixture of solid carbon dioxide and acetone.Thecarbon monoxide was treated similarly but, in this case, the coolant was liquid nitrogen.Before use each of the traps was baked in order to remove impurities from previous experi-ments.In these experiments high purity (99.99 %), polycrystalline nickel and copper foils wereused.These were supplied by Goodfellow Metals.The exposures quoted in this paper are expressed in langmuirs (L) where 1 L = Torr s(1 Torr = 133.3 Pa). The pressures used in these experiments were such that the totalexposure time was between 10 and 60 s.RESULTSNICKELThe sample was thoroughly cleaned by ion etching and spectra were run to ensurethe cleanliness of the surface. Fig. l(a) shows the mass spectrum from ~i clean surface.The lack of any peaks corfesponding to carbon or oxygen-containing species shoul42 ADSORPTION OF co ON Ni A N D CUbe noted. The peaks at mass numbers 23 and 39 are due to sodium and potassiumrespectively. Obviously, some estimate of the level of these impurities must be made.The reported value for the sputtering coefficient of K+ l 3 is found to be lo3 timeshigher than that for Ni+ and, since the potassium and nickel peaks in fig.1 areapproximately the same height then the surface concentration of potassium must beof the order of 0.1 %. The surface concentration of sodium is expected to be similarbut there is no data on its sputtering coefficient. The value of 0.1 % is only a roughestimate since Hagstrum used potassium primary ions. The value of the sputteringcoefficient when argon ions are used is not expected to be very different. The massspectrum of negative secondary ions did not indicate the presence of any impurities.The temperature of the clean sample was then reduced to 77 K.Upon the admission of 2 L of carbon monoxide at this temperature, the intensityof the peaks due to Ni+ (mass numbers 58 and 60) increased approximately 5 timesand a large pair of peaks was observed at mass numbers 86 and 88 due to NiCO+.Fairly intense peaks also appeared at 1 16, 118 and 120 due to Nii but only relativelysmall peaks at 144, 146 and 148 due to Ni2CO+, see fig.I@).Upon the admission of a further 2 L of carbon monoxide the intensity of the Ni+peaks increased by about 12 % of its former value and that of the NiCO+ peak by25 % of its original value. There was no significant change in the heights of theNi2CO+ peaks or the Niz peaks.Ni'Ni; LNa' kmle mle(4 (b)FIG. 1 .-SIMS spectrum of nickel surface (a) after argon ion etching, (b) after admission of 2 L carbonmonoxide at 77 K.Admission of a further 10 L of CO caused a similar, but far less marked, changein the appearance of the spectrum while a further 10 L made no significant change,i.e., saturation had occurred at a dosage of less than 14 L.On allowing the sample to warm to room temperature the intensities of the NiCO+and Ni2CO+ signals decreased until, at room temperature, their intensities were onlyabout 10 % of those at 77 K.Fig. 2 shows a comparison of the spectrum obtaineM. BARBER, J . C.VICKERMAN AND J . WOLSTENHOLME 43after saturation at 77 K with that obtained after heating to room temperature; notethat the spectrum at 295 K was run at a higher sensitivity.Similar spectra were obtained starting from a clean nickel surface at room tem-perature except that saturation did not occur until about 40 L of carbon monoxidehad been admitted.The value obtained by Williams et aZ.I4 using UPS and XPSwas only 22 L. There were also small peaks corresponding to Ni2C+ and Ni20+,the intensities of these were approximately equal and about 10 % of the intensityof the Ni2CO+ peaks, see fig. 3(a).After a very large number of doses of CO, small peaks appeared in the spectrumwhich could be assigned to Ni(C0): and Ni(C0);.Upon heating the sample to 390 K, after saturation of the surface at 295 K, theintensities of the NiCO+ peaks quickly diminished and could not be detected at about370K. There was no significant alteration in the intensities of the peaks due toNil, Ni2C+, NizO+ or Ni2CO+ and no new species appeared.A further dose of 40 L carbon monoxide was admitted at this temperature whichcaused the Nil, Ni2C+, Ni20+ and NizCO+ signals to double in intensity but a furtherNi:NNimle mle(a) (b)FIG.2.--Comparison of SIMS spectra (a) after saturation with carbon monoxide at 77 K and (b)after warming the saturated surface to room temperature. Note that (b) was run at 10 times greatersensitivity.20 L of carbon monoxide made no significant difference. Prolonged heating at 390 Kand several large doses of carbon monoxide (each dose being about 0.5Torr for5 min) caused a build-up of the Ni2C+ peak relative to that of the Ni,CO+ until noNi2C0 remained on the surface, fig. 3(b).This is in agreement with the resultsobtained by Joyner and Roberts.6COPPERAgain, the sample was thoroughly cleaned and the SIMS spectrum was used asan effective check on the cleanliness of the rrurfacc, fig. 4(44 ADSORPTION OF co ON Ni AND CUAdmission of 20 L doses of carbon monoxide at 77 K caused a build-up of theCuCO+ peaks (mass numbers 91 and 93) until saturation occurred at about 80 L.Apart from Cuf and CuCOf the only other peaks appearing in the spectrum wereNi,'NiCOdx 3 1 NiN i'Ni20+ Ni,C+IL.1 1 1 1 I 1 1 I I I140 120 100 00 6 0FIG. 3.-SIMS spectrum nickel surface (a) after saturation with CO at room temperature, (b) afterlarge doses of CO at 390 K.c u;c u*x 11 10CU'K'FIG. 4.-SIMS spectrum of copper foil (a) after argon ion etching, (6) at 77 K after a saturation doseof carbon monoxideM.BARBER, J . C. VICKERMAN AND J. WOLSTENHOLME 45due to Cu,'. The intensities of the Cu,' peaks are too low for them to be visible infig. 4(b) but could be seen when the sensitivity of the instrument was increased. Thisshould be compared with nickel where the mass spectrum under these conditionsindicated the presence of the species Ni,CO+ as well as NiCO+.temperature /KFIG. 5.-Variation of intensity of peak due to CuCOf as the temperature is raised from 77 to 295 K.1 1 1 1 1 1 1 1 1 1 1 1 ~190 170 150 1 3 0 . 110mleFIG. 6.-SIMS spectrum of copper foil after saturation at room temperature.When the surface had been saturated at 77 K the temperature was raised to 295 Kwhile the signal due to CuCO+ was continuously monitored.The intensity of thissignal is plotted against temperature in fig. 5. Note that there is a discontinuity onthis curve which occurs at approximately 195 K and that the CuCO+ value drops tozero at room temperature.Upon the admission of 1000 L CO at room temperature the intensities of the Cu46 ADSORPTION OF co ON Ni AND CUpeaks increased markedly and new peaks appeared at 154, 156 and 158 correspondingto Cu2CO+, see fig. 6, and saturation occurred at about 5000 L.Ton causedthe appearance of various carbide species, fig. 7. These were assigned to CuC;,CuCf , Cu2C+, Cu,Ct, Cu,Cl and Cu,C,+. There were also very small peaks whichcould be assigned to Cu,CO,+, suggesting, perhaps, that the carbon is formed bydisproportionation of the carbon monoxide followed by the desorption of carbondioxide.Allowing carbon monoxide to flow over the sample at 390 K andCU'U U ~ 2ao 210 wo 170 ' i s 0 130 110 9 0 7 0mleFIG.7.-Appearance of carbide species in SIMS spectrum after flowing CO over the surface at7.DISCUSSIONNICKELIn the temperature range 77-295 K two carbon monoxide-containing secondaryions were observed in the spectrum. One is due to carbon monoxide bonded to onenickel atom and the other to carbon monoxide bonded to two nickel atoms. Sincethe ratio of the intensities of the peaks due to these two forms is roughly constantin this temperature range, it might be argued that the singly bonded carbon monoxideis merely a fragment of the larger species, formed by the bombardment by the argonions.If this were the case then it would be expected that this ratio would remainconstant at all temperatures. This was not so. The NiCO+ peak had completelydisappeared from the spectrum at about 370K while that of Ni2CO+ remained.Thus, we assume that these two species are due to two distinct surface species andthe one does not derive from the other.We now suggest possible surface structures from which these secondary ions arederived. Obviously, it is not possible to give precise structures from a SIMS study.Since there is no evidence to say that adsorbed carbon monoxide is bonded to ametal surface via the oxygen atom, it seems likely that NiCO+ is formed from aprocess schematically illustrated in fig.8(a)M. BARBER, J . C. VICKERMAN A N D J . WOLSTENHOLME 47One can envisage a number of processes leading to the formation of Ni,CO+;these are illustrated in fig. 8(b)-(d).When considering a possible surface structure which would give rise to Ni2CO+it must be remembered that it must be different, in some way, from that which givesrise to NiCOf.The surface structure illustrated in fig. 8(b) appears to be identical with that in (a).It is, perhaps, possible that there are two types of site on the nickel surfaces and onboth of these sites carbon monoxide is bonded in a linear manner. From one ofthese sites sputtering gives rise to only NiCO+ and from the other only Ni2CO+ butthis seems unlikely.Secondary Ion(a 1 I I 1 I l l I 1p?J N N iFIG. 8.-Possible surface processes which would give rise to the appearance of NiCO+ and Ni2CO+.Process (c) suggests that the carbon monoxide is dissociatively adsorbed.It wasfound that at temperatures where carbon monoxide is known to adsorb dissocia-tively,6 we obtained peaks corresponding to Ni2C+ and Ni,O+. It is reasonable toassume, therefore, that if carbon monoxide were dissociatively adsorbed at roomtemperature then we would obtain peaks corresponding to the same species. Thusit is unlikely that process (c) gives rise to Ni2CO+.It is logical, therefore, to ascribe the appearance of Ni2CO+ to a structure of thetype illustrated in fig. 8(4. The idea of a “bridge” bonded carbon monoxidemolecule is supported by the evidence of i.r.spectro~copy,~ as mentioned in theintroduction. However, the correlation is not complete since the initial adsorptionof carbon monoxide is i.r. inactive whereas we observe “ linear ” and “ bridged ”forms even at low exposures.The decrease in intensity of the peaks due to these two species as the temperatureis raised from 77 to 295 K may be due either to a surface reaction in which carbonmonoxide is lost or to desorption.If a surface reaction were taking place then it is fair to assume that it would beone of the following :orIn either case one would expect to see extra peaks occurring in the SIMS spectrum,these were not observed. Thus, it seems likely that the reduction in the amount ofadsorbed carbon monoxide is due to desorption.toads -3- Cads+Oads * ca~ls+$~2(g)2coads -+ Cads + C02ads Cads + c02(g)48 ADSORPTION OF co ON Ni AND CUOn raising the temperature further we found that none of the linear Ni-C-0 isleft on the surface at 370 K.Although at this stage, there is a buildup of carbon andoxygen on the surface and so some dissociation must be taking place, this is small.Unfortunately, no infrared experiments have been carried out at this temperature.It would be interesting to know whether the band assigned to the linear structuredisappears at this temperature.Our observation that, on heating the adsorbed carbon monoxide at 390 K in thepresence of carbon monoxide, a surface carbide is formed, is in agreement withthe results of work by Joyner and Roberts.6 Our results would suggest alsothat the mechanism of this carbide formation is one of dissociation rather thandisproportionation since, as well as Ni2C+, we observe peaks due to Ni20+ but therewere no peaks which could be assigned to a structure containing carbon dioxide.It is possible to make a rough estimate of the relative coverages of the linear andbridged forms of adsorbed carbon monoxide but it is first necessary to make certainassumptions about sputtering coefficients.The sputtering coefficient is defined asthe number, N,, of secondary ions produced for each primary ion falling on the target,where No is the flux of primary ions.see ref. (11) and (15).when carbon monoxide is adsorbed the variation is assumed to be such thatKi = Ni/NOFor a more detailed account of sputtering coefficients and their determinationAlthough the ratio of sputtering coefficients for Ni; and Nil species may varyThus, the relative coverages of NiCO and NizCO can be estimated from theequationWhere Ii+ is the total secondary ion current for species i, summing over all oftheisotopes for a particular species.Using this approximation we find that about 30 %of the adsorbed carbon monoxide is in the bridged form and 70 % in the linear form.It must be emphasised that, as a result of the above assumption this is a fairly crudeapproximation.COPPERIn contrast with the results obtained from the adsorption of carbon monoxide onnickel at 77 K, adsorption on copper at this temperature produces only the CuCO+species and no Cu,CO+.Using a similar argument to that used for NiCO+ it isbelieved that this is derived from a surface structure analogous to that in fig. 8(a).This is in direct agreement with the results obtained from i.r. studies where thesingle, narrow band is assigned to a linearly bound carbon monoxide structure ratherthan to a bridged structure.Despite the fact that carbon monoxide is only bound in a linear form at 77 K,it is evident from our desorption curve, fig. 5, that desorption occurs from two distinctsurface species. The discontinuity on this curve at about 195 K indicates the onsetof the desorption of a second type of adsorbed species at this temperature. Thesecond species is completely desorbed at room temperature, since the signal diminishesto zero at this temperatureM.BARBER, J . C. VICKERMAN AND J . WOLSTENHOLME 49If adsorption is studied at77 K the i.r. band and the surface potential increase in proportion with coverage upto 8 = +.* This indicates that there is only one type of adsorption up to this coverage.As the coverage is increased LEED investigations suggest a compression of theadsorbed layer; the intensity of the i.r. band remains constant but the band shiftsto higher frequencies and the surface potential decreases. This indicates that asecond type of adsorption is occurring at 8 > 0.5. If, flow, the metal is warmedfrom 77 K, desorption occur's and these processes are reversed, the species formedsecond is desorbed first, complete desorption occurring at 195 K, the temperatureat which we observe the discontinuity on our desorption curve.At room temperaturethe i.r, band disappears and the surface potential returns to zero indicating completedesorption. It will be seed from fig. 8 that we, too, observed complete desorptionat room temperature.Our adsorption studies at room temperature reveal the secondary ion speciesCuzCO+ but there is no evidence for the presence of CuCO+. Arguing as before, itis probable that this is derived from a surface structure analogous to that shown infig. 8(d).Saturation of the surface with this species only occurs after a total of 5000 L.The incorporation of carbon into the metal lattice can account for the appearanceof carbon-containing secondary ions in out spectra at 390 K.The formation of thevarious secondary ions can be illustrated by the schematic representation of thesurface, fig. 9. The dotted lines in this diagram encircle groups on the surface whichThis too, is in agreement with previous studies.'*FIG. 9.-Suggested surface structure which would give rise to various carbide slructures observed inthe spectrum. 0, copper ; 0, carbon.could give rise to the secondary ions Cu,C,+ and Cu,C,+, similar boxes would showhow the other species could arise, The limitation of this approach is that it does notexplain the absence in the spectrum of species such as CuC+ and CuCl.The formation of carbon on the surface is due either to decomposition or dis-proportionation of the carbon monoxide.Disproportionation is favoured here sincethere was a weak signal in some of the spectra which could be assigned to Cu,CO;.The uncertainties both in the way the carbon arises and the structure it subsequentlyadopts indicate that it is necessary to study this system further.ASSESSMENT OF TECHNIQUEIn cases where comparable work has been done using other techniques, the resultsobtained from SIMS are consistent. Furthermore, this method will give resultsdirectly and often more conveniently. It is also capable of providing informationfrom a wide variety of samples (e.g., metal foils, thin films, single crystals, supportedmetals as well as insulators) over a wide temperature range and with good resolution.Its value for elucidating surface cleanliness has already been noted.An important point with any method of analysis is the extent to which the methodof study affects the system being analysed.As may be seen from our spectra the ion* Ref. (7) puts this at 8 = 450 ADSORPTION OF CO ON Ni AND Cubombardment does not seem to affect the surface process. For example, it is fairlyobvious that induced fragmentation does not occur since the species which might beregarded as fragments either have different thermal properties from the ‘‘ parent ”species (as in the caSe of NizCO+ and its possible fragments NiCO+, Ni,C+ or Ni20+)or do not appear in the spectrum (e.g., NiC+ or NiO+). Thus we can say that thespecies we observe faithfully reflect the situation on the surface of the sample.Furthermore, the process of bombardment does not affect the surface in such away as to alter its properties. This we may deduce both from the consistency of ourresults with those from other techniques and from the reproducibility of our resultswith the same metal sample.A further point to note is that the sensitivity of SIMS is such that we are ableto observe species which have not been reported previously in the literature (e.g.,a bridged structure for adsorbed carbon monoxide on copper).We are grateful to Vacuum Generators Ltd. for the generous loan of the equipmenton which this work was carried out and also to the S.R.C. for a Research Studentshipawarded to J. W.G. Wedler, H. Papp and G. Schroll, Surface Sci., 1974,44,463.H. H. Madden, J. Kuppers and G. Ertl, J. Chern. Phys., 1973,58,3401.J . C. Tracy, J. Chem. Phys., 1972,56,2736.A. M. Bradshaw and J. Pritchard, Surface Sci., 1969, 17, 372.T. E. Edmonds and R. C. Pitkethly, Surface Sci., 1969,15, 137.R. W. Joyner and M. W. Roberts, J.C.S. Farudzy I, 1974,70,1819.M. A. Chesters and J. Pritchard, Surface Sci., 1971, 28,460.J. C. Tracy, J. Chem. Phys., 1972,56,2748.R. W. Joyner, C. S. McKee and M. W. Roberts, Surface Sci., 1971,26,303.A. Bennhghoven, Surface Sci., 1973, 35,427.’ M. A. Chesters, J. Pritchard and M. L. Sims, Chem. Cornm., 1970, 1454.I2 M. Barber, P. K. Sharpe and J. C. Vickerman, to be published.I3 I. A. Abroyan and U. P. Laurov, Soviet Phys., Solid State, 1962,4,2382.l4 P. J. Page, D. L. Trim and P. M. Williams, J.C.S. Faraday I, 1974,70, 1769.l5 Ya. M. Fogel, Soviet Phys. Uspekhi, 1967,10,17

ISSN:0300-9599    

DOI:10.1039/F19767200040

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

One-electron Reduction Reactions with Enzymes in SolutionA Pulse Radiolysis StudyR. H. BISBY AND R. B. CUNDALLChemistry Department, University Park, Nottingham NG7 2RDJ. L. REDPATH? AND G. E. h A M S *Cancer Research Campaign Gray Laboratory, Mount Vernon Hospital,Middlesex HA6 2RNReceived 17th March, 1975At pH 8 and above, hydrated electrons react with ribonuclease, lysozyme and a-chymotrypsinto form transient products whose spectra resemble, but are not identical to, those for the RSSR-radical anion already known for simple disulphides. Assuming a value for the extinction coefficientsimilar to that for RSSR- in simple disulphides, only a fraction of the hydrated electrons are shownto react with the disulphide bridges : the remainder react at other sites in the protein molecule, suchas histidine, tyrosine and, in lysozyme, tryptophan residues, giving rise to comparatively weak opticalabsorptions between 300 and 4OOnm.This has been substantiated by studying the reaction ofe;, with subtilisin Nuuu (an enzyme which does not contain disulphide bridges), with enzymes in whichthe sulphur bridges have been oxidised and with some amino acid derivatives.On lowering the pH of the solution the intensity of the RSSR- absorption diminishes as the pro-tonated histidine residues become the favoured reaction sites. In acid solutions (PH 2-3) the tran-sient optical absorptions observed are due to reactions of hydrogen atoms with the aromatic aminoacids tyrosine, tryptophan and phenylalanine.The CO; radical anion is only observed to transfer an electron to disulphide groups in ribonucle-ase, although the effect of repeated pulsing shows that some reaction must occur elsewhere in theprotein molecule.In acid solutions, protonation of the electron adduct appears to produce theRSSRH. radical, whose spectrum has a maximum at 340 nm.One-electron reduction processes in non-metal containing enzymes can lead toinactivation, although with widely differing efficiencies. Such processes can be use-fully studied by radiation-chemical methods including pulse radiolysis. le3 Numerousstudies on the radiation chemistry of free amino acids and peptides in solution showthat both H atoms and hydrated electrons react rapidly with several classes of thesecompounds and the results have been used to predict possible sites of reductive attackin en~yrnes.~Pulse radiolysis studies have shown that hydrated electrons react rapidly withseveral enzymes and proteins to form a species with transient absorption spectra,' 9 2 9similar to those for the one electron adducts of simple disulphides.6*7 However,the proportion of the total elq yield which appears to be trapped at the disulphidelinkages in the enzymes varies considerably.The object of this study was to investigate the sites of, and mechanisms of, one-electron reduction processes by the hydrated electron and the formate radical anion,CO,, in solutions of four simple non-metal containing enzymes, lysozyme, ribo-nuclease (RNase), a-chymotrypsin and subtilisin NOVO (an enzyme which does notcontain any disulphide bridges).t present address : Department of Medical Physics, Michael Reese Hospital, Chicago, Illinois60616, U.S.A.552 ELECTRON REDUCTION OF ENZYMESEXPERIMENTALThe irradiation source was a linear accelerator which delivered 0.2 p s pulses of electronsof energy 1.8 MeV. The test solutions were irradiated in a quartz cell of path length 2 cmand transient changes in the optical absorption properties were recorded by fast spectro-photometry.For measurement of transient spectra, doses of 1-2krad were used. Dosi-metry was carried out using the thiocyanate dosimeter and small fluctuations in single-pulsedoses were normalised by charge collection methods. Full details of the pulse radiolysisequipment, associated circuitry * and the method of solution preparation have already beenpublished.Triply-distilled water was used throughout as diluent. All solutes were of thepurest grade available and were used as supplied. t-Butyl alcohol was purified by multiplerecrystallisation. N-acetylhistidine and N-glycyltyrosine were obtained from the SigmaChemical Co. Ltd.Ribonuclease (chromatographically purified), lysozyme (6 x crystake) and a-chymo-trypsin (3 x crystalline) were obtained from Miles-Serevac Ltd. Subtilisin No00 was a giftfrom Novo Industries A/S, Copenhagen.The method of Hirs l o was used for the performic acid oxidations. Both RNase andlysozyme oxidised by this method had less than 2 % of the activity of the native enzymestowards cytidine+2'-3'-cyclic phosphoric acid and the cell wall of Micrococcus Zysodekticus l2respectively.RESULTS(a) ONE-ELECTRON REDUCTION OF ENZYMES CONTAINING CYSTINE ATReactions of the enzymes with e; were followed by pulse radiolysis in N,-saturatedsolutions containing each enzyme and t-butyl alcohol as an OH scavenger.Thisalcohol reacts rapidly with OH radicals (k = 5.2 x lo8 dm3 mol-' s-l),13 but veryslowly with H atoms (k < lo5 dm3 mol-I s-l) l4 and hydrated electrons. Fig. l(a)shows the transient optical absorption spectra formed on pulse radiolysis of neutraldeoxygenated solutions of lysozyme, RNase and a-chymotrypsin each containinglo-' mol dm-3 t-butyl alcohol. The enzyme concentration, 4 mg ~ m - ~ for eachsolution, was suficiently high to ensure that all the hydrated electrons formed at thisdose per pulse were scavenged by the enzyme [fig.I@)].The relative absorptivity at 420 nm for the transient product obtained fromlysozyme is about three times greater than that from either RNase or a-chymotrypsin.The molar extinction coefficients at 420 nm for the electron adducts of most simpledisulphides lie in the range from 0.8-1.0~ lo4 dm3 mol-' cm-l,'' l5 although slightlylower values (5-8 x lo3 dm3 mol-' cm) have been reported for some cyclic RSSR-radicals.'. l6 Assuming a similar value of 9 x lo3 dm3 mol-I cm-1 for the extinctioncoefficient of RSSR- in the enzymes, the proportions of the initial yield of e i whichbecomes localised at the disulphide bridges in the three enzymes are : lysozyme 65,RNase 25 and a-chymotrypsin 22 %.This shows that electrons are trapped at othersites in the enzymes and that the proportions of electrons trapped at these sites variesfrom enzyme to enzyme.Fig. 2 shows the transient absorption spectrum of the electron adduct of thedisulphide compound, cystamine,6 normalised at the maximum to that of the lysozymeelectron adduct at pH 7. The spectra are clearly different in the wavelength regionbelow 400nm. One possible explanation of this is that the shorter wavelengthabsorption in the enzyme solutions is due to the product of electron attack at sitesother than disulphide bridges. In addition, reaction of hydrogen atoms with theenzymes may give rise to the absorption.NEUTRAL pR. H. BISBY, R.B. CUNDALL, J . L. REDPATH AND G. E. ADAMS 53The various possibilities were investigated by studying, as a function of pH, oneelectron reduction reactions of (i) samples of RNase and lysozyme, in which thedisulphide bridges had been oxidised by performic acid, (ii) the enzyme, subtilisinNovo, which contains neither cystine nor cysteine residues, and (iii) some simpleN-acylamino acids.0.06 -b -4 0 i .- 0.04-U a03 0 0 400 5 0 0 6 0 00.06\F[enzyme]/mg ml-'FIG. 1 . 4 ~ ) Transient spectra from dtaerated neutral solutions of some enzymes containing 10-Imol dm-j t-butyl alcohol ; A, lysozyme (4 mg ~ m - ~ ) , pH 7.0 ; 0, ribonuclease (4 mg ~ m - ~ ) , pH8.6 ; 0, a-chymotrypsin (4 mg ~ m - ~ ) , pH 6.8 ; dose = 2 krad/pulse, spectra measured 20 ps after thepulse.(b) Effect of enzyme concentration on the transient absorption at 410 nm following pulseradiolysis of neutral deaerated enzyme solutions containing lo-' mol dm-3 t-butyl alcohol ; A,lysozyme, pH 7.0 ; 0, ribonuclease, pH 8.6 ; 0, a-chymotrypsin, pH 6.8 ; dose = 2 krad/pulse,spectra measured 20 ps after the pulse.(b) REACTIONS OF REDUCING RADICALS WITH OXIDISED ENZYMESTreatment of RNase and lysozyme with performic acid lo oxidises the cystineresidues to sulphonic acids and the methionine residues to the corresponding sul-phoxides. Fig. 3(a) shows the transient absorption spectra obtained on pulseradiolysis of N2-saturated solutions of the oxidised enzymes (2 mg ~ m - ~ ) containing10-1 mol dnr3 t-butyl alcohol. For both enzymes, comparison with fig.l(a) showsthat oxidation of the disulphide linkages leads to a large reduction in the intensityof the 420 nm transient absorption maximum. In oxidised lysozyme, the spectrumcould not be measured below 420nm because of the high absorptivity of the un-irradiated solution. This was not so for the RNase derivative which shows a transientabsorption band with a peak at 350 nm and an extinction of about half that measuredat this wavelength for native RNase. This suggests that in the native enzyme, at leas54 ELECTRON REDUCTION OF ENZYMESI I I I I300 400 5 0 0 600AImFIG. 2.-Comparison of the electron-adduct spectra of lysozyme and cystamhe; 0, lysozyme4 mg ~ m - ~ , lo-' mol t-butyl alcohol, pH 7; dose = 2 krad/pulse, spectra measured 5 ps afterpulse ; 0, cystamine, data from ref.(13) (normalised at 410 nm).wavelength jnmFIG. 3.-Transient spectra from pulse radiolysis of deaerated enzyme solutions containing 10-lmol dm-3 t-butyl alcohol ; (a) 0, performic acid oxidised RNase, pH 8,2 krad/pulse ; 0, performicacid oxidised lysozyme, pH 8, 1 krad/pulse, enzyme concentration = 2 mg ~ m - ~ ; (b) subtilisin(4 @INovo (4 mg 0, pH 8.0 ; 0, pH 2.7, 1 krad/pulse.some of the absorption below 4OOnm is not associated with reduction of the di-sulphide bridges. The absorption in the oxidised enzyme is not due to attack at theoxidiscd methionine residues, since no transient absorptions were observed over thewavelength region 300-6OOnm on reaction of e 4 with methionine sulphoxide insolution.We conclude, therefore, that the absorption bands below 400m in thR . H . BISBY, R . B . CUNDALL, J . L. REDPATH AND G . E. ADAMS 55two native enzymes must be due to electron reaction with either the peptide linkagesor with reactive side groups in the non-sulphur-containing amino acids.(c) ONE-ELECTRON REDUCTION OF subtilisin NovoFig. 3(b) shows transient spectra obtained on pulse radiolysis of deaerated solutionsof subtilisin Novo (4 mg ~ m - ~ ) containing 10-1 mol dm-3 t-butyl alcohol at pH 8 and2.7. As expected, there is no absorption maximum at 420nm in neutral solution,but the absorption spectrum at shorter wavelengths is similar to that from oxidisedRNase. The rate constant for reaction of e; with subtilisin Novo at pH 7.3 wasobtained by measurement of the decay of the e,71 absorption at 600 nm in the presenceof lo-' mol dm-3 t-butyl alcohol and was found to be 1.8 x 1Olo dm3 mol-l s-l.The transient spectrum obtained from solutions at pH 2.7 is considerably moreintense than that found at pH 8.Further, at pH 2.7 the decay of the transient spec-trum can be resolved into two components. Fig. 4 shows the transient spectrum fromsubtilisin Novo at pH 2.7 measured immediately after the pulse and after 100 p s &lay.The latter spectrum decays relatively slowly over several milliseconds. The spectrumof the rapidly-decaying transient, which has a half life of -65 p s , obtained bydifference shows a maximum at 350 nm.wavenumber /nmFIG. 4.Transient spectra from pulse radiolysis of oxygen-free solutions of subtilisin Now (4 mg~ r n - ~ ) and lo-' mol dm-3 t-butyl alcohol at pH 2.7, 0, immediately after the pulse ; 0, after 100 ps ;A, difference spectrum : dose = 1 krad/pulse.(d) ONE-ELECTRON REDUCTION OF SOME N-ACYLAMINO ACIDSIn an attempt tobdentify the radical responsible for the 350 nm transient absorptionproduced in the enzyme systems, some experiments were carried out with two simpleamino acid derivatives.Information in the literature on one electron reduction of simple peptides is con-cerned mainly with aliphatic compounds and transient spectra are observed on pulseradiolysis of such systems 17* l 8 with maxima generally in the region 400-440 nm.These have been assigned to radicals produced by deamination.In large peptidesand enzyme proteins where only one such N-terminal amino group is present, radicalsof this type cannot be major reaction products. The peptide bond also has consider-able reactivity with c& in compounds such as triglycine. The radical products fromsuch reactions have the electron localiacd on the carbonyl group and only absorb inthe ultraviolet with maxima at 265 nrn.17* l56 ELECTRON REDUCTION OF ENZYMESFree aromatic amino acids are generally more reactive than aliphatic amino acidswith the hydrated electron and usually react to give species with transient absorp-tion maxima in the region around 350 nm,19-21 e.g., histidine, tyrosine and tryptophan.Since these spectra appear to be associated with reactions of e; with the aromaticrings, it would be anticipated that these amino acids, when present in peptide chains,would still react with e; to give similar transient radicals.Two simple aromaticamino acid derivatives were used to investigate this possibility.0.010-0.00sN-ACETYLHISTIDINEFig. 5 shows transient absorption spectra formed on pulse radiolysis of oxygen freesolutions of 5 x lo-( mol dm-3 N-acetylhistidine containing lo-' rnol d ~ n - ~ t-butylalcohol. The spectrum in neutral solution shows a maximum at 360m and issimilar to that formed by one-electron reaction with free histidine2* At higher pHvalues, the intensity of the absorption maximum decreases as is shown in the insetto fig. 5.?-I IOL 3b0 3 5 0 400 450wavelength/nmFIG.5.-Transient spectra from pulse radiolysis of oxygen free solutions of N-acetylhistidine (5 xmol dm-3) and lo-' mol dm-3 t-butyl alcohol, 0, pH 6.7; 0, pH 9.5; dose = 1 krad/pulse,spectra measured 5 p s after the pulse. Inset : Effect of pH on optical density at 360 nm.N-GLYCYLTYROSINEmoldm-3 of N-glycyltyrosine containing 10-1 mol dm-3 t-butyl alcohol are shown infig. 6, for neutral and alkaline pH values. At pH 7, the spectrum is again similar tothat for the one-electron reduction product of free tyrosine 20* 21 with a peak at340 nm. In alkaline solution, the peak is shifted to 380 nm.The transient product spectra obtained from oxygen-free solutions of 5 x(f) EFFECT OF pH ON TRANSIENT SPECTRA FROM LYSOZYMEAND RIBONUCLEASETransient spectra obtained from pulse radiolysis of RNase solutions containing10-1 mol dm-3 t-butyl alcohol are shown in fig.7(a). The spectra change appreciablywith pH. At pH 7 and above, the major absorption band is at 410 nm, but in acidsolution this maximum disappears and is replaced by a broad absorption in the ultra-violet. At pH 2, practically all hydrated electrons react with H30+ ions to form R. H. BISBY, R. B. CUNDALL, 3 . L. REDPATH AND G . E. ADAMS 570.0 I5 c1 1 1 130 0 3 5 0 400 450 500A/nmFIG. 6.-Tramient spectra from pulse radiolysis of oxygen-free solutions of N-glycyltyrosine (5 xmol dm-3) containing lo-’ rnol dm-3 t-butyl alcohol measured 5 ps after 2 krad/pulse, 0, pH 7 ;0, pH 11.I I I3 0 0 4 0 0 5 00 6 0 0Lwavelength/nmFIG.7.-(a) Transient spectra from pulse radiolysis of oxygen-free solutions of ribonuclease (4 mg~ r n - ~ ) containing 10-’- mol dm-3 t-butyl alcohol, 0, pH 8.5 ; 0, pH 7.0 ; A, pH 6.4 ; V, pH 2.2 ;dose = 2 krad/pulse, spectra measured 5 ps after the pulse. Inset : Effect of pH on optical density at410 nm. (6) Transient spectra from pulse radiolysis of oxygen-free solutions of lysozyme (4 mg ~ m - ~ )containing lo-‘ mol dm-j t-butyl alcohol, 0, pH 7.0; 0, pH 5.0; A, pH 3.7; A, pH 3.0; 0,pH 2.0 ; dose = 2 krad/pulse, spectra measured 5 ,as after the pulse . Inset : Effect of pH on opticaldensity at 410 nm58 ELECTRON REDUCTION OF ENZYMESatoms; the spectrum obtained at this pH, therefore, is attributed to reactions ofH atoms with the enzyme.Near neutral pH, where the H30+ concentration is verylow, the hydrated electrons will react directly with the enzyme. Nevertheless, thereis a clear pH effect in this region : a decrease in pH from 8.6 to 6.4 is sufficient toremove a large proportion of the absorption peak at 410 nm. The observed pH effectstrongly suggests that at the lower pH value reactions of e& at sites other than cystineresidues are more favourable.Fig. 7(b) shows data obtained from similar experiments with lysozyme.(g) ONE-ELECTRON REDUCTION OF RIBONUCLEASE BY FORMATE RADICALSIn N,O-saturated solutions containing formate ions, the CO; radical anion isformed as the sole radical product :N20+ea; + N2+OH-+OH* (1)OH+HCO, -+ H,O+CO, (2)H+HCO, 4 H,+CO,. (3)The rate of electron transfer from CO; to simple disulphides is a factor of lo3 greaterthan that for reaction with simple amino acids and peptides that do not containsulphur bridges.mold ~ n - ~ sodium formate at pH 8 are pulse-irradiated, an absorption at 410 nm isobserved which increases in intensity with repeated pulsing [fig.S(u)]. The numberWhen N,O-saturated solutions of RNase (I mg ~ r n - ~ ) containing 4 x0.03(a) 0.02300 0.0 Ito 2 0 30 4 0 50 6 0 70w -0-.- s +1650 aO.Oi5--*-*---;00/+O-O--o 300(6)I I 8 t10 2 0 30 40number of pulsesFIG. 8.-Formation of a transient absorption at 410111x1 with repeated pulse irradiation of NeOsaturated solutions of ribonuclease and 4 x 1C2 mol dm-' sodium formate at pH 8 ; (0) 1 mgribonuclease. Doses (rad/pulse) given against the curves.ribonuclease ; (6) 0.5 mgof pulses required to reach a maximum transient absorption intensity at 410 nm varieswith pulse size and at small doses per pulse no sipificant absorption appears untilthe solution has reccivcd some tens of pulses. ThC enzyme concentration also aircctR. H. BISBY, R . B . CUNDALL, J . L . REDPATH AND G . E. ADAMS 59the total dose required before the maximum transient intensity is observed as shownin fig. 8(b). The effect of temperature on the formation of the 410 nm absorption dueto reaction of COY with RNase (1 mg CM-~) is shown in fig. 9 : there is a markedI I I I I I I I I I3 0 4 0 5 0 6 0 7 (temperature/"CFIG. 9.-Effmt of temperature on the transient 410 nm absorption formed by pulse radiolysis of NzOsaturated solutions of ribonuclease and 5 x mol sodium formate at pH 5.9, dose = 2 had/pulse, 0, after 1 pulse ; A, after 10 pulses ; 0, after 30 pulses.change in behaviour above 55°C.Transient spectra obtained from reaction of CO;with RNase are shown in fig. 10 at various pH values. These spectra were obtainedfrom solutions which had previously been irradiated until a maximal absorption wasobserved. At pH 7.5 the observed transient spectrum contains a single peak at 410nm, but at lower pH this is replaced by another transient absorption with a peak at340-350 nm. The pH effect on the peak intensities at 410 and 350 nm is shown inthe inset to fig. 10.PH I - -. .A.wavelength/nmFIG. lO.-Transient spectra from pulse radiolysis of NzO saturated solutions of ribonucleast (1 mg~ r n - ~ ) and 4 x mol dm-3 sodium formate having previously received between 10 and 40 pulses,dose = 2 krad/pulse, spectra measured 35 ps after the pulse, 0, pH 7.5 ; 0, pH 5.9 ; A, p H 4.6 ; 'I,pH 3.9 ; v , pH 3.1.Inset : Effect of pH on the optical densities of the transients at ; 0, 410 nm ;0,350 nm.Repeated pulse irradiation of N,O-saturated solutions of subtilisin Novo (3 mgmol dm-3 sodium formate did not reveal any transient containing 4 xabsorptions in either neutral or acid solutions60 ELECTRON REDUCTION OF ENZYMESDISCUSSIONThe spectral evidence shows that hydrated electrons can react with differentresidues in the enzymes. The effects of pH on the transient absorption spectraindicate which amino acid residues are involved.In addition to reaction with di-sulphide groups, the absorptions at approximately 350 nm in the native enzymes,oxidised proteins and amino acid derivatives show that reaction can also occur withthe imidazole, phenolic or indole groups of histidine, tyrosine or tryptophan, becausesimilar absorptions are observed following reaction of e; with the free amino acids.In RNase solutions, the absorption at 410 nm decreases significantly on changingthe pH from 8.6 to 6.4 [fig. 7(a)]. This change occurs over the pH region where theimidazole rings of histidine residues in RNase undergo protonation (pK values5.1-6.4).22 The reactivity of e; towards protonated histidine (k = 7 x lo9 dm3 mol-1s-l) is considerably greater than that of unprotonated histidine (k = 6 x lo7 dm3mol-1 s-l) and is comparable with that of cystine (k = 1.3 x 1Olo dm3 mol-' s-I atpH 6.1).23 It follows that as the histidine residues in RNase are protonated theybecome much more favourable reaction sites for the hydrated electron.The effectof pH on the electron-adduct spectrum of RNase is compatible with such a changein reaction site : the intense absorption of the RSSR- radical at 410 nm is replacedby the absorption at 360 nm of the histidine radical which has a rather lower extinctioncoefficient ( E ~ ~ ~ = 1200 dm3 mot1 cm-l). An alternative explanation of the de-crease of the 410 nm absorption with decreasing pH which has to be considered isthat the RSSR- radical is protonated at the lower pH;RSSR-+ H+ + RSSRH.-+ RS-+ RSH.For glutathione, protonation of the RSSR- radical occurs with an apparent pK0f5.2.~~The intermediate RSSRH. radical is usually short-lived in simple disulphides andthe observed product is the RS- radical, which typically absorbs at 330-350 nm witha very low extinction coefficient (E,,, = 300-600 dm3 mol-' ern-').'' 24 The RSSRHspectrum has been identified in the pulse radiolysis of lipoic acid where dissociationinto RS- and RSH is hindered presumably because of the ring structure. ThisRSSRH radical absorbs at 385 nm with an extinction coefficient of 6.9 x lo3 mol-1cm-l.'This value is not much smaller than the extinction coefficient of RSSR- of lipoicacid ( E ~ ~ ~ = 9.2 x lo3 dm3 mol-I cm-' at pH 7.8).' By contrast, the overall intensityof the electron adduct spectrum of RNase at pH 6.4 is about half that at pH 8.6, andappears to be a composite spectrum.The RSSR- spectrum from RNase is notreplaced by another single absorption at shorter wavelengths with a similar extinctioncoefficient which would be expected if RSSRH were to be produced. This effect iseven more apparent with lysozyme [fig. 7(b)].The spectrum obtained from RNase at pH 2.2 will be due to products formed byreaction of H atoms produced by the rapid protonation of e i . The reactivities ofhydrogen atoms with amino acids at acid pH are known 25 and can be comparedwith hydrated electron reactivities. Whereas the rates of reaction of e; with tyrosineand phenylalanine are a hundred fold lower than that with cystine, H atoms reactwith tyrosine (k = 1.9 x lo9 dm3 mol-' s-l) and phenylalanine (k = 8 x lo8 dm3mol-l s-l) with rate constants which are only a factor of 10 or less lower than thatwith cystjne (k = 8 x lo9 dm3 mol-' s - ' ) .~ ~ Therefore, the reactivity of tyrosineand phenylalanine residues in RNase would be much higher with H atoms than withe.9 and their corresponding adduct spectra would be expected to be much moreevident in acid than at neutral pH. Fig. 7 shows this to be the case. At pH2.2there is a relatively intense spectrum with maxima at 350 and 320 nm. The absorption(4R. H . BISBY, R. B. CUNDALL, J . L . REDPATH AND G . E. ADAMS 61at 350nm is similar to that of the H atom adducts of tyrosine.21 We assign themaximum at 320 nm to the H-atom adduct of phenylalanine since a similar band hasbeen observed following reaction of H atoms with free phenylalanine at neutral andacid pH,l8* 26 At pH 2.2, any reaction of H atoms with cystine would give rise toRS- radicals which absorb very weakly at 330-350 nm.The similarity between theH atom adduct spectra of RNase at pH 2.2 and subtilisin Novo at pH 2.7 confirmsthat any contribution to the spectrum from RNase at pH 2.2 from sulphur radicalsis negligible.The spectrum produced by one-electron reduction of lysozyme [fig. 7(b)] can beinterpreted in much the same way as those of RNase. The major differences arethat in lysozyme a larger fraction of the e i yield reacts to form RSSR- and that thecurve for optical density at 410 nm as a function of pH is displaced to lower pH byabout 1.5 units relative to the corresponding curve for RNase.This is due to differ-ences in the relative reactivities of the two residues (cystine and histidine) in the twoenzymes as shown by the larger yield of RSSR- in lysozyme above pH 8. Anotherdifference is that, unlike RNase, lysozyme contains tryptophan, an amino acid whichis very reactive towards H atoms (k 2 2.3 x lo9 dm3 mol-' s - ' ) . ~ ~ The hydrogenatom adduct spectrum of tryptophan contains a peak at 310-320 nm l9 which, invicw of the high rate constant, must contribute to the H atom adduct spectrum oflysozyme [fig. 7(b), pH 21 at these wavelengths.The assignment of some absorptions in the product spectra formed by one-electronreduction of RNase and lysozyme to non-sulphur containing radicals is confirmed bythe results obtained with subtiZisin Navo.Despite the lack of cystine or cysteineresidues in this enzyme, the hydrated electron reacts with it at a rate (k = 1.8 x 10"dm3 mol-' s-l) which is similar to that for ribonuclease (k = 1.0 x 1 O ' O dm3 mol-Is-' at pH 7.1). At pH 8, the electron adduct spectrum of subtihin No00 has a broadshoulder at 350 nm which may be due to some combination of histidine, tyrosine ortryptophan radicals in addition to a peak at 310 nm which also appears in the electronadduct spectrum of tryptophan.lg. 2o The hydrogen atom spectrum of subtilisinNovo is similar to those for RNase and lysozyme, consisting of absorptions between300 and 400 nm due to H atom attack on the ring-containing amino acids.The fasterdecaying part of the two component spectrum which has a half life of - 65 p s containsa peak at 350 nm which is similar to the spectrum of the hydrogen atom adduct oftyrosine. 21The spectra following reaction of RNase with the formate radical CO, differsignificantly from those formed by reaction with e; and H atoms. After suitablepre-irradiation of the solution, the radical anion CO; reacts with RNase at pH 7.5to give a single transient with a maximum at 420 nm which is clearly the spectrum ofthe RSSR- radical anion. At low pH the spectrum is changed to one with a maxi-mum at 340 m. Repeated pulse irradiation of subtilisin Novo solutions containingformate does not give rise to a 340 nm transient in acidic solutions.Therefore, the340nm band in the RNase solutions must be due to some type of sulphur radical.The extinction of the 340 nm band appears slightly larger than of the 420 nm bandin neutral solution, so it is unlikely to be due to RS. radicals which generally haveextinction coefficients at least an order of magnitude less than those of the correspond-ing RSSR- radical anions. However, the RSSRH. radical of lipoic acid has anextinction coefficient similar to that of its radical anion. We conclude that the 340 nmband observed from reaction of CO; with RNase is due to an RSSRH- radical formedby rapid protonation of RSSR- :H +v.fastCOY +RSSR --+ RSSR' + RSSRH. ( 5 62 ELECTRON REDUCTION OF ENZYMESAt pH 3.1 any contribution from C02H will be insignificant ; this radical has a pKof only 1.4.27 Whereas reaction of COY with RNase gives rise to an absorption at340 nm in acid solutions, the corresponding absorption in lipoic acid, which has beenassigned to the RSSRH., is at 385nm.The difference may arise because the 5-membered ring of lipoic acid may be subject to strain and cause a change in theabsorption spectrum.The spectra obtained by one-electron reduction of RNase by CO, and e; inslightly acid solutions are strikingly different. The band containing the prominentpeak at 340-350nm obtained by reduction with CO, at pH3.9 and assigned toRSSRH is different from the less intense and less defined absorption produced byreduction of RNase by eLq at pH 6.4.This is in agreement with our interpretationof the effect of pH on the spectrum formed from e i attack on this enzyme. Thespectral changes are not due to protonation of RSSR- to give RSSRH, but resultfrom a change in the reaction site from cystine residues to the histidine residues asthe pH falls below the pK of the protonated imidazole ring of histidine.The reason why RNase solutions require pre-irradiation before CO; is able totransfer an electron to the disulphide bridges of the enzyme is not established. Pre-sumably, COT reacts in the first instance with a residue we have so far been unableto identify. This primary reaction causes conformational changes of the enzymewhich make the disulphide bridges more accessible to the CO; radicals which onlythen can react to form RSSR-.This is supported by the effect of temperature on themanner in which RSSR- is formed as the solutions are repeatedly pulse irradiated(fig. 9). The 410 nm absorption of RSSR- is more easily formed above 55-60°C, thetemperature range over which RNase is known to undergo conformational transi-tions.2This work was supported by grants from the Cancer Research Campaign.G. E. Adarns, J. L. Redpath, R. H. Bisby and R. B. Cundall, IsraelJ. Chem., 1972,10,1079.T. Masuda, J. Ovadia and L. I. Grossweiner, Int. J. Rudiation Biol., 1971, 20,447.R. Braams and M. Ebert, Int. J. Radiation Biol., 1967,13,195 ; N. N. Lichtin, J. Ogdan andG. Stein, Biochim. Biophys. Acta, 1972,263,14 ; N.N. Lichtin, J. Ogdan and G. Stein, Biochint.Biophys. Acta, 1972,276, 124.R. Braams, Radiation Res., 1967, 31, 8.G. E. Adams, R. B. Cundall and R. L. Willson, in Ctlernical Reactioity and Biological Role ofFunctional Groups in Enzymes, ed. R. M. S. Smellie (Academic Press, London and New York,1970), p. 171 ; J. R. Clements, D. A. Armstrong, N. V. Klassen and H. A. Gillis, Canad. J.Chem., 1972,50,2833 ; N. V. Klassen, J. W. Purdie, K. R. Lynn and M. D'Iorio, Int. J. Radia-tion Biol., 1974, 26, 127; G. E. Adams, K. F. Baverstock, R. B. Cundall and J. L. Redpath,Radiation Res., 1973,54,375 ; P. B. Roberts, Int. J. Radiation Biol., 1973,24,143 ; G. E. Adams,R. L. Willson, J. E. Aldrich and R. B. Cundall, Int. J. Radiation Biol., 1969, 333.ti G.E. Adams, G. S. McNaughton and B. D. Michael, in The Chemistry ofIonization and Excita-tion, ed. G. R. A. Johnson and G. Scholes (Taylor and Francis, London, 1967), p. 281. ' M. Z. Hoffman and E. Hayon, J. Amer. Chern. SOC., 1972,94,7950.G. E. Adams, J. W. Boag and B. D. Michael, Trans. Faraday SOC., 1965, 17,349.R. L. Willson, Int. J. Radiation Biol., 1970, 17, 349.New York, 1967), vol. XI, p. 51.lo C. H. W. Hirs, in Methods in Enzymology, ed. C. H. W. Hirs (Academic Press, London andl 1 E. M. Crook, A. P. Mathias and B. R. Rabin, Biochem. J., 1960,74,234.l2 D. Shugar, Biochem. Biophys. Acta, 1952, 8, 302.l3 L. M. Dorfman and G. E. Adams, Reactivity of the HydroxyI Radical in Aqueous Solutions,National Standard Reference Data System, NSRDS-NBS-46 (National Bureau of Standards,Washington, U.S.A., 1973).l4 M. Anbar and P. Neta, Int. J. Appl. Radiation Isotopes, 1967, 18, 493.l 5 G. E. Adams, R. C. Armstrong, A. Charlesby, €3. D. Michael and R. J. Willson, Trans. FuraduySOC., 1969, 65, 732R . H. BISBY, R . B . CUNDALL, J . L. REDPATH AND G. E. ADAMS 63l6 J. L. Redpath, Radiation Res., 1973,64,364 ; P. C. Chan and B. H. J. Bielski, J. Amer. Chem.l7 M. Simic and E. Hayon, Radiation Res., 1971, 48, 244.l9 R. C. Armstrong and A. J. Swallow, Radiation Res., 1969, 40, 563.2o M. Farragi and I. Pecht, Israel J. Chem., 1972, 10, 1021.21 J. Feitelson and E. Hayon, J. Phys. Chem., 1973, 77, 10.22 J. H. Bradbury and H. A. Scheraga, J. Amer. Chem. Soc., 1966,88,4240 ; G. C. K. Roberts,23 R. Braams, Radiation Res., 1966, 27,319.24 A. Shafferman, Israel J. Chem., 1972,10,725.25 P. Neta and R. H. Schuler, Radiation Res., 1971, 47, 612.26 N. N. Lichtin and R. Shderman, Radiation Res., 1973, 60,432.27 G. V. Buxton and R. M. Sellers, J.C.S. Favoday I, 1973,69,555.28 J. F. Brandts and L. Hunt, J. Amer. Chem. SOC., 1967,89,4826; J . Hermans and H. A. Scheraga,SOC., 1973,95,5504.J. P. Mittal and E. Hayon, J. Phys. Chem., 1974,78,1790.D. H. Meadows and 0. Jardetsky, Biochemistry, 1969, 8, 2053.J. Amer. Chem. SOC., 1963, 85, 3866; W. A. Klee, Biochemistry, 1967, 6, 3736

ISSN:0300-9599    

DOI:10.1039/F19767200051

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Conductance of some CobaIt(II1) Complexes in Water at 25°CPart 1 .-Conductance of Salts of trans- and cis-dinitrobis(ethylenediamine)cobalt(rrI)BY ALAN D. PETHYBRIDGE" AND DAVID J. SPIERS?Department of Chemistry, The University, Whiteknights, Reading, Berks. RG6 2ADReceived 4th April, 1975Precise conductivity results are reported for aqueous solutions of seven salts of trans- and cis-[c~(en)~(NO~)~]+. They are analysed in terms of the full Pitts equation and the association con-stants for the salts, although small, are found to increase with increasing radii of the ions, beingparticularly large for ci~-[Co(en),(NO~)~]I. Contrary to popular belief, tran~-[Co(en)~(NO~)~]ClO~is also appreciably associated in dilute aqueous solution. Rate constants for the very slow aqua-tion of these cations are also reported.The existence of outer-sphere complexes has been widely postulated and variousmethods of determining the association constants of these complexes have beendeveloped.A comprehensive survey of earlier work has been published.' Moststudies of outer-sphere complex formation in aqueous solution have been made withlabile inner-sphere complexes or with concentrated solutions and the values obtainedfor the association constants of the outer-sphere complexes are often discrepant anddepend very much on the assumptions made in their calculation. Measurement ofthe electrolytic conductivity of dilute solutions of inert symmetrical complex saltsshould provide a more certain method of measuring the association constants of anyouter-sphere complexes formed, but most work in this direction has been withmultiply-charged salts, where association is likely to be greater for purely electro-static reasons, or with unsymmetrical salts where the resulting outer-sphere complexis still charged.The theoretical conductance equations of Pitts 2* and Fuoss canbe applied to symmetrical multiply-charged electrolytes, although not to unsym-metrical ones, but they are more reliable when used for 1 : 1 electrolytes. The outer-sphere association constants of 1 : 1 electrolytes are likely to be much smaller andboth very precise conductance measurements and a sophisticated analysis of the resultsare necessary to obtain meaningful values of these constants. Only the early workof Densham on the complex ion [ C r ( ~ y ) ~ F ~ l + had been published when we startedthis work, but during its progress the molar conductivities of some halogen substi-tuted acetato- and some oxalato-complexes of cobalt(II1) were reported and arediscussed later.In this work salts of trans- and cis-dinitrobis(ethylenediamine)cobalt(m), [Co(en),-(NO2),]+, were chosen for study because earlier reports in the literature had claimedthat these inner-sphere complexes are inert with respect to isomerization 8* andaquation.*-io By comparing the association constants for salts with a commonanion of the cis-cation with those for the trans-cation, we should be able to investigatethe importance of dipole moments in outer-sphere complex formation.In fact, boththe complex ions were found to aquate very slowly, the conductance increasing byapproximately 0.01 % per hour at 25°C so that the aquation of these ions can reallyt present address : International Nickel Ltd., European Research and Development Centre,Wiggin Street, Birmingham B16 OAJ.6A.D. PETHYBRIDGE A N D D. J. SPIERS 65only bz detected by precise conductimetry. The rate was sufficiently fast to necessitatethe replacement of the usual concentration-run technique of conductance measure-ment by the determination of the electrolytic conductivity of individually-preparedsolutions extrapolated back to the time of preparation. Hence, in addition to themolar conductivities, rate constants for the aquation of these cations are also reported.EXPERIMENTALAPPARATUSThe apparatus and thermostat used for these conductance measurements have beendescribed e1sewhere.l' The conductivity celIs were of the Marsh-Stokes type.12 The elec-trodes were not platinized as there is some evidence that blackened electrodes catalyse thedecomposition of ColI1 complexes.' All conductances were measured at six frequenciesand were extrapolated to infinite frequency.The cells, which had constants of 0.211 06,1.406 3 and 5.559 3 cm-l, were calibrated to 0.01 % with solutions prepared from vacuum-dried, twice-recrystallised AnalaR potassium chloride, using the semi-empirical equationsof Lind, Zwolenik and Fuoss l4 and Chiu and Fuoss l5 for the molar conductivity of potas-sium chloride.All solutions were prepared by weight, corrected to vacuum and the concentrationswere calculated using density measurements made on one of the more concentrated solutionsat 25°C using two density bottles calibrated with distilled water.A linear relationshipbetween density and molality was assumed in all cases for our solutions which are allsufficiently dilute for this to be reasonable.All measurements on these complexes were made by the single-point technique describedbelow, to allow for the time-dependence of the conductivity caused by the slow aquationof the cation. Cell constants obtained by this approach agreed with those found by themore usual concentration run method within experimental error. A special routine forwashing, rinsing and drying the cells and preparing the solvent was developed l6 so that alow and reproducible water conductivity could be obtained. This was always in the range2.2k0.3 x lo-' S cin-l, about four times the electrolytic conductivity of pure water, so thatthe maximum solvent correction to be deducted is less than 1 % for the most dilute solution.In a single-point run 0.05-2 g of the purified salt was weighed on an Oertling model 141balance which permits estimation, using extreme care, of the sixth decimal place. Theweighed salt was then placed in the cell reservoir, a weighed quantity of thermostattedconductivity water16 added by nitrogen pressure and the time noted.After stirring magneti-cally for a few minutes the reservoir was connected to the cell and immersed in the thermo-stat.After one hour conductance measurements were started and repeated at hourlyintervals for 6 h. For most salts the conductance increase was of the order of 0.01 % perhour and was linear in time. The conductance value at zero time was obtained by graphicalextrapolation and the rate constant for the aquation was calculated from the slope. Theconductances of solutions of the salt [Co(en),(NO,),][Co(edta)] increased by about 0.1 %per hour and yielded slightly curved conductance against time plots which were fitted to aquadratic expression by a least-squares technique.PREPARATION OF COMPOUNDSConductivity water and materials of the highest quality grade conveniently available(usually AnalaR) were used throughout. Full details of the preparation and purificationof these salts are given e1~ewhere.l~tr~ns-[Co(en)~(NO~)~]NO~.Several different samples of this salt T were prepared bythe method of Holtzclaw, $heetz and McCarthy.s The sample used for conductance measure-ments was purified by recrystallising twice from boiling conductivity water and was thendried in vacuo at 100°C. The solubility at room temperature is approximately0.06 mol dm-3.Analysis : found C 14.4, H 4.9, N 29.7 ; calculated C 14.4, H 4.8, N 29.4 %.trnns-[C~(en),(NO~)~]CIO~ was prepared by mixing equimolar quantities of almostsaturated solutions of T and sodium perchlorate. The yellow precipitate was filtered off,1-66 CONDUCTANCE OF CO"' COMPLEXESwashed with alcohol and ether, recrystallised twice from boiling conductivity water and wasfinally dried in vacuo at 100°C.The solubility at room temperature is estimated to be0.015 mol dm3. Analysis : foundC 12.9, H4.4, N 22.6 ; calculated C 13.0, H 4.35, N 22.7 %.trans-[C~(en)~(NO~)~]Cl was prepared by passing a near-saturated solution of T down anion-exchange column containing analytical grade Amberlite resin IRA400 in the chlorideform. The middle portion of the eluate was reduced to one tenth by evaporation and theproduct precipitated by the addition of a large excess of acetone. The product was purifiedby dissolving in the minimum quantity of water, 10 cm3, and filtering into 90 cm3 of acetone.Air-dried samples of the salt proved to be the monohydrate but the non-hygroscopic anhyd-rous salt was formed on heating in vacuo at 100°C and was used for the conductance measure-ments.The solubility at room temperature was estimated to be greater than 2.5 mol dm-3.Analysis for anhydrous salt : found C 15.7, H 5.4, N 27.5 ; calculated C 15.7, H 5.3, N27.4 %.trans-[C~(en)~(NO~),]Br was prepared and purified in a manner similar to that of thechloride. The solubility at room temperature was estimated as approximately 0.5 rnol dm3.Analysis : found C 13.6, H 4.7, N 23.9; calculated C 13.7, H 4.6, N 23.9 %.tram-[C~(en),(NO~)~]I was not prepared directly by ion exchange because of the dangerof oxidation to iodine during the lengthy ion-exchange process. Instead a saturated solutionof the chloride was prepared by ion exchange as described above and an equimolar quantityof saturated potassium iodide solution was added.The precipitate was filtered off andrecrystallised twice from boiling conductivity water, being protected by an atmosphere ofnitrogen at all stages. The product was finally dried in vacuo at 40°C. The solubility atroom temperature was estimated as approximately 0.12 mol d~n-~. Analysis : found C12.2, H 4.1, N 21.1 ; calculated C 12.1, H 4.05, N 21.1 %.tran~-[Co(en)~(NO~),]F was also prepared by ion exchange of a saturated solution of T.The purified product analysed as the trihydrate, but on heating in vacuo at 40°C the non-hygroscopic monohydrate was formed which was used for the conductance measurements.On heating to 100°C in vacuo the anhydrous salt was obtained but this proved to be extremelyhygroscopic.Analysis of monohydrate: found C 15.7, H 5.9, N 27.4, F 6.4; calculatedC 15.6, H 5.9, N27.3, F 6.2 %.from trans-[Co(en),CI,]Cl which was in turn prepared by the method of Bailar and Rollin-son.18 At all stages during the preparation and purification of the salts of ~is-[Co(en)~-(NOz)J+ care was taken to ensure that the temperature did not exceed 60°C since isomeriza-tiong to the trans form becomes significant above 65°C. The final product was purified byrecrystallising twice from water at 55"C, cooling the solution in an ice-salt bath before filter-ing. The product was dried in vacuo at 40°C. The solubility at room temperature isapproximately 0.035 mol dm3. Analysis : found C 14.3, H 4.9, N 29.5 ; calculated C 14.4,H 4.8, N 29.4 %.cik-[C~(en)~(NO~),]r.As with the trans-salt, this was prepared from the chloride (itselfobtained by ion exchange) by precipitation with saturated potassium iodide solution afterconcentration at 40°C on a rotary evaporator in the absence of oxygen. The salt was re-crystallised from water at 40°C and was dried in vacuo at 40°C. The solubility at room tem-perature is approximately 0.07 mol dm3. Analysis : found C 12.1 , H 4.1, N 21.2 ; calculatedby fractionalcrystallisation from a solution containing equimolar proportions of trans-[C~(en)~(NO~),]Cland potassium ethylmediaminetetra-acetatocobaltate(m) (K[Co(edta)J, whose preparationis described in Part 2). The product was recrystallised from boiling water and dried in vacuoat 100°C.The solubility at room temperature is approximately 0.2 mol dm-3. Analysis :found C 27.3, H 4.7, N 18.0; calculated C 27.2, H 4.6, N 18.1 %.cis-[C0(en)~(NO~)~]N0~, C, was prepared by the method of Harbulak and AlbinakgC 12.1, H 4.05, N 21.1 %.trans-[C~(en)~(NO~)~][Co(edta)] was prepared following SchwarzenbachRESULTSThe inolar conductivities of eight salts are given in table 1 together with the rateconstants for the aquation process. The aquation of tran~-[Co(en)~(NO~)~]F proA. D. PETHYBRIDGE AND D. J . SPIERS 67ceeded rapidly so neither conductivities nor rate constants are included here. Thisphenomenon will be discussed later. All conductance readings have been convertedto (absolute ohm)-l or siemens.104 cA106 k104 cA106 k104 cA106 k104 cA106 k104 cA106 k104 cA106 k104 cA106 k104 cA106 kTABLE 1 .-MOLAR CONDUCTIVITIES AND RATE CONSTANTS(c/mol dm-3, A/S an2 rnol-', klmin-')7.913 6102.932.36.667 0104.061.910.942101.382.85.486 297.4261.610.86291.8404.324.888100.132.114.48695.3343.017.50758.75220trunr-[Co(en)~(NO~)zlCl29.370 35.786 59.201 73.554100.59 100.13 98.561 97.7843.0 2.6 2.4 2.3trans-[Co(en)z(NOz)zIBr9.491 3 11.602 25.898 50.082103.525.218.268100.463.217.78295.7330.859.73087.7230.637.33 198.6913.417.51594.9891.732.21957.08418103.27 101.69 99.8431.7 2.0 1.2trms-[Co(en)z(NOd~JI28.654 57.610 72.35899.390 97.270 96.3542.0 1.6 1.2f runs-[Co(en)~(NOz)zlNOj26.193 46.20 1 80.47594.942 93.403 91.4731.1 0.7 0.5trons-[Co(en)~(NO2)2ClO472.076 101.45 125.1787.121 85.605 84.6311.1 1.9 1.8cis-[Co(en)Z(NOz)&41.865 53.22498.154 97.1752.2 1.5cis-[Co(en)z(NOz)dNO~35.803 58.907 79.71693.209 91.681 90.4541.2 1.3 5.4trms-ICo(en)z(NOz) zl[Co(edta)l67.821 110.145 154.7954.563 52.276 50.54618 19 1799.76396.6202.171.53498.6083.1102.9794.8221.691.86590.9471.1107.4889.1380.9123.9695.6441.993.21397.5292.7127.0893.7421.3137.9289.0452.0150.2187.4710.6114.6396.6232.5DISCUSSIONA" AND KA VALUESOur general method of fitting conductance data in terms of A", KA and d, thedistance of closest approach of free ions, is based on that of Duer, Robinson andBates,20 and has been described elsewhere.We used the full conductivity equationsof Pitts 2* and Fuoss and Hsia in our analysis rather than the various expandedversions of the two equations as we have found that for water, just as for hexamethyl-phosphorotriamide,' the actual parameters producing a statistical best fit of the datavary significantly according to which expanded version is chosen. Accordingly weconsider that any detailed interpretation of precise conductance data should be interms of the full equations even if this means an added complexity of computation.All calculations were performed on the CDC7600 computer at U.L.C.C. using theprogram SEEKER written in FORTRANIV. Throughout this work we reportparameter values obtained using the Pitts (P) equation.In general the Fuoss-Hsia(FH) equation gives a comparable fit but with slight systematic changes in the para-meters which will be noted68 CONDUCTANCE OF COMPLEXESThe simplest method of fitting the data is to assume that the salts are completelydissociated in aqueous solution, in which case the association distance d and contactdistance a are identical. Values of A" and a which fit the data for each salt are givenin table 2. The FH equation gives a similar fit but at a values larger by approximately0.3 A. The values of the deviation function cA( %), defined asOA( %) = {c[loo(l -A~~lc/Aobs>12/(n-2>): (1)TABLE 2.-ANALYSIS BY FULL PITTS EQUATION. BEST-FIT PARAMETERS ; ELECTROLYTES TREATEDAS FULLY DISSOCIATEDsalt 4 Am/S cm2 mol-1 a-4 %Itran~-[Co(en)~(NO~) 2]C1 0.52 105.33 0.04trans-[ C0(en)~(N0~)~]Br 0.28 106.24 0.05tran~-[Co(en)~(NO~)~]I 0.11 104.24 0.05trans-[ Co(en) (NO2)2]C104 0.10 94.61 0.07trans-[Co(en)z (NO2)2]N03 0.26 99.38 0.04ci~-[Co(en)~(NO~)~]N0~ 0.12 98.56 0.09where n is the number of experimental points, are quite reasonable but the values ofa are all absurdly small for such large ions.In fact ~is-[Co(en),(NO,)~]I requiresa negative value of a (which cannot be determined by SEEKER) for the best statisticalfit, so it is omitted from table 2. Consequently, it is logical to introduce an additionalvariable, the association constant KA, and the best-fit parameters Am, KA and d areshown in table 3 for the P equation.Not surprisingly, smaller values of a,( %) arenow obtained and these results, which are obtained by the single-point technique,always show a unique position of best fit with each equation. In general the fit withthe FH equation is equally good but occurs at values of d, A" and KA which are largerby approximately 0.9 A, 0.010 S cm2 mol-1 and 0.20 dm3 mol-1 respectively.TABLE 3 .-ANALYSIS BY FULL PITTS EQUATION. BEST-FIT PARAMETERS ; ELECTROLYTES TREATEDAS ASSOCIATEDsalt d / A Awls em2 mol-1 KA/drn3 mol-1 aKA 0.4 %Itrans-[Co (en) (NO 2 ) ,]C1trans-[Co(en),(N02),]Brtrans-[Co(en),(NO,),]Itrans-[ Co (en) (NO ,) 2]N0tran~-[Co(en)~(NO~),]ClO~~is-[Co(en)~(NO,)~]I~is-[Co(en),(NO,)~]N03tran~-[Co(en)~(NO~),][Co(edta)]3.023.053.053.123.163.103.064.28105.36106.27104.3399.4394.69105.5098.6762.361.591.952.522.082.606.322.558.050.130.410.130.160.120.180.230.930.030.040.030.020.050.060.060.21However, we have shown that when comparing results of different workers forthe same system, or indeed different runs by the same worker on the same system,it is necessary to compare Am and KA values at a common d to obtain results that aremutually consistent.The actual value of d is not critical within the range 2-8 A buta convenient value is the Bjerrum critical distance q (= z2e2/2DkT) which is 3.58 Ain water at 25°C. Table 4 shows the Am, KA and cA( %) values obtained for the fitat d = q using the P equation.The FH equation gives an equally good fit underthese conditions with A" values about 0.005 S cm2 mol-1 larger and KA values about0.20 dm3 mol-l smaller than those in table 4. We accept that for these salts q is lessthan the sum of the crystallographic radii. However, all the points of statisticaA . D . PETHYBRIDGE AND D. J . SPIERS 69best-fit obtained in table 3 occur at even smaller values of d, and we believe that dcannot be interpreted as a physically meaningful distance, but that it is an artefactof the conductivity equations primarily determined by the charge on the ions andthe dielectric constant of the solvent. Similar calculations at d = 2q simply raise allthe KA values by about 1 .O dm3 mol-l. Because of the arbitrary nature of the valuechosen for din table 4, the exact values of the association constants are of no absolutephysical significance and should only be quoted in conjunction with the value of dselected.On the other hand, association constants calculated for a fixed value ofd should be capable of a valid comparison, since they are free of the random elementthat is inherent in the best-fitting procedure when A*, KA and d are all adjusted.Although the values of crA( %) are slightly larger than those for our conductance dataobtained by the concentration-run technique (see Part 2), they probably represent amore realistic estimate of the errors involved, as each measurement is quite independentof the others in all but the purity of the solute.TABLE 4.-ANALYSIS BY FULL PITTS EQUATION : d = 4 (3.58 A) : ELECTROLYTES TREATED ASASSOCIATEDsalt Am/S cm2 mol-1 &/dm3 mol-1 OKA GA(%)trans-[Co(en),(NO,),]Cl 105.36 1.82 0.13 0.03trans-[Co (en) (NO ,) ,]Br 106.27 2.16 0.41 0.04rrans-[C~(en)~(NO~)~]I 104.33 2.73 0.13 0.03trans-[C~(en)~(NO~)~]NO~ 99.43 2.27 0.16 0.02tuans-[C~(en)~(NO~)~]ClO~ 94.69 2.78 0.12 0.05cis-[Co (en), (NO 2 ) ,]I 105.50 6.52 0.18 0.06cis-[C~(en),(NO~)~lNO 98.67 2.77 0.23 0.06The results in table 4 show that the association constants of the outer-spherecomplexes increase in the order Cl < Br < NO3 < I M C104.The high associationconstant for outer-sphere complex formation for trarzs-[C~(en)~(NO,),]ClO~ is ofparticular interest and is rather disturbing in view of the fact that perchlorates areoften added as swamping electrolytes in equilibrium and kinetic studies because oftheir low tendency to form inner-sphere complexes (and nitrates are usually the secondchoice).This suggests that in such a medium many of the ions of interest are notfree but are in fact paired with the perchlorate ions of the medium. Burnett 2 2 hasshown from kinetic studies that such outer-sphere complex formation with perchlorateis significant and must be allowed for in studies on the rates of exchange of, forexample,[CO(NH~),(H~~)]~+ + C1- + [Co(NH3)=,C1I2+ + H20.We have shown 21 that there is a strong correlation between the value of KA at anyfixed d value such as the Bjerrum critical distance and the sum of the crystallographicradii for a wide range of salts. The results for most of the salts studied in this workagree with this pattern, shown in fig.1, where we have also plotted results for thosesalts where two independent sets of precise results are in good agreement. With oneexception, our complexes all lie close to the band containing the KA values of the othersalts. The exception is cis-[C~(en),(NO,)~]I where association is likely to be enhancedboth by the dipole moment of the cation (the cis-nitrate is also slightly more associatedthan the trans-nitrate) and by the polarizability of the iodide. The association constantof Bu,NI is also much larger 21 than can be predicted on account of its size from fig. 1.The ionic radii used in plotting fig. 1 were taken from standard corn pi la ti on^.^^^ 24aThe value of 4.3 A for the radius of trans- or ci~-[Co(en),(NO,)~]+ was found from asimple geometrical calculation using bond lengths in similar complexe~.~ We hav70 CONDUCTANCE OF CO"' COMPLEXEScommented 21 on the fact that the trend in KA values with increasing Y is the reverse ofthat predicted by the Bjerrum theory of association.The consequences of the trendobserved in fig. 1 will be discussed further in a later paper.From the A" values shown in table 2 for the various salts it is possible to show,using published d2 that the limiting molar conductivities of traits- and cis-[Co(en),(NO,),]+ are 27.7 * 0.4 and 27.4f 0.3 S cm2 mol-1 respectively. The largescatter in these values is undoubtedly due to varying amounts of hydrolysisproducts produced during the preparation and purification of the compounds andnot entirely removed during recrystallisation procedures.This was particularly true++00 2 4 6 8&lystlAFIG. 1 .-Plot of KA values at d = q using the P equation against the sum of the crystallographic radiiof the ions. x alkali metal halides, 0 alkali metal oxosalts, + tetra-alkylammonium halides,A salts studied in this work.of tran~-[Co(en),(NO,)~]Cl. The values of KA obtained are not seriously affected bythese small changes in A". The point for tran~-[Co(en),(NO,)~][Co(edta)] is notshown in fig. 1 (its coordinates are 7.68 dm3 mol-1 and 8.6tf) because its A@' value,see table 3, is approximately 9 conductance units higher than would be expected fromthe individual ionic conductances.Therefore the association constant of the pure1 : 1 double complex salt would be rather different but probably still large. The trans-[ Co(en),(NO,),JF, which aquated much more rapidly, also had A" approximately9 conductance units too high. However, the scatter on the individual results wassuch that a meaningful value of KA could not be obtained, the value with d = q being4.8k4.5 dm3 mol-l.We have also reanalysed the precise conductivity data for similar salts in theliterature ' 9 and the values of A" and KA which fit at d = q for the Pitts equationare given in table 5. These parameters show general agreement with the trends of K,with r reported in table 4 and fig. 1, especially the high association constant for[Co(ox)(en),]I.The results for the acetatocobalt(rI1) complexes ' are not includeA . D. PETHYBRIDGE AND D . J . SPIERS 71because these salts were all aquated relatively quickly and only 3 or 4 experimentalpoints are reported for each salt.RATES OF AQUATIONFor most of these complex salts the aquation of the cation leads to an increase inthe conductance of the order of 0.01 % per hour and could only be observed bysuch a sensitive technique. Even this change could be masked by a change in thetemperature of only 0.005"C so the values obtained for the rate constants for theaquation are bound to be imprecise. However, the values for the rate constantsreported in table 1 were obtained from each experimental run and show quite goodagreement with no obvious trend with increasing concentration or dependence uponthe anion.These values of the rate constant, k, were obtained from the time-dependence of the electrolytic conductivity, dK/dt, from the equationc dt 100- 83.65 x C'k = !!!fTABLE 5.-ANALYSIS OF LITERATURE RESULTS BY THE FULL PITTS EQUATION, d = 4salt n m / S cm2 mol-1 KA/dm3 mol-1 UKA UA( "/u,[Cr(PY),F2lC104 a 86.71 4.88 0.58 0.02[Co(ox)(en),]Cl 98.52 -0.19 0.27 0.02[Co(ox)(en)2lI 98.69 7.33 0.23 0.03[~o(ox)(en)~l~10~ 90.26 0.95 0.18 0.01a ref. (5) ; b ref. (6).[Cr(PY)4F21SCNba 84.97 6.29 3.34 0.04[Co(ox)(en)zlBf; 100.31 2.28 0.08 0.01in which the Onsager limiting conductance law has been used and Am(NO;) is takenas 72.1 S cm2 r n ~ l - ' . ~ ~The average first-order rate constant for the aquation of trans- or cis-[Co(en),-(NO,),]+ is 2 x min-l in the presence of C1-, Br-, I-, NO: and C102.Thereappears to be no previous determination of k for these ions which had previouslybeen reported as inert to aquation.*"*The value of k for trans-[Co(en),(NO2),][Co(edta)] is some 10 times greater thanthat obtained for the above salts. The pH of a nitrogen-saturated 0.015 mol dm-3solution was 6.6 and the pH of a similar solution of K[Co(edta)J was 6.2 suggestingthat the anion is responsible for the low pH and that the free hydrogen ions appearto catalyse the aquation of the trans- complex ion. This is presumably due to theequilibriafor which Schwarzenbach l9 has quoted some evidence.The conductance-time curves of tran~-[Co(en),(NO~>~]F were much steeper andmarkedly curved. From the initial slope of these curves, obtained by a curve-fittingprocedure, a first-order rate constant some 2 x lo6 times larger than that for the othertrans- complexes was obtained.The pH of a 0.01 mol dm-3 solution was 5.1 threehours after preparation, but increased to 5.9 when the solution was left overnight inthe cell. This may be due to the reactionSiO,(s) + 4H+ + 6F- + SiFz-+2H20which would also explain why the conductance of the solution, although initially[Co(edta)J- + H20 + [Co(edta)(H,O)]- + [Co(edta)(OH)I2- + H72 C 0 N D U C T A N C E 0 F CO"' C 0 M P L EXESincreasing rapidly, was found to be decreasing by approximately 0.1 % per hour thefollowing day. The free hydrogen ions were probably due to the presence of a smallamount of HF; which was selectively absorbed from the unbuffered fluoride solutionused to convert the IRA-400 resin to the fluoride form, well-known to be an un-favourable exchange, and which was then eluted during the preparation cycle.It is difficult to estimate from these results the quantitative effect of hydrogen ionsupon the aquation, but the evidence is that they appear in the rate equation to apower higher than one.One of us (D.J. S.) is grateful to the S.R.C. and the University of Reading forfinancial support.Note added in proof. We have reanalysed our data using the latest Fuoss equation (J. Phys. Chem.,1975,79, 525). The best-fit values of d occur at around 3.9 A, rather higher than those recorded intable 1, but lower than those reported by Fuoss for alkali metal halides.The new equation withd = (I yields ha values 0.02 S cm2 mol-l larger than those from the P equation in table 4 but KAvalues 0.7 dm3 mol-' lower.M. T. Beck, Co-ordination Chem. Rev., 1968,3, 91.E. Pitts, Proc. Roy. SOC. A, 1953, 217, 43.E. Pitts, B. E. Tabor and J. Daly, Trans. Faraday Soc., 1969, 65, 849.R. M. Fuoss and K.-L. Hsia, Proc. Nat. Acad. Sci. U.S.A., 1967, 57, 1550; 1968, 58, 1818.A. B. Densham, Trans. Faraday SOC., 1937, 33, 1513.M. Yokoi and K. Kuroda, Bull. Chem. SOC. Japan, 1971,44,3293. ' E. Kubota, Nippon Kagaku Zasshi, 1971,92, 1112. * H. F. Holtzclaw, Jr., D. P. Sheetz and B. D. McCarthy, Inorg. Synth., 1953, 4, 176.E. P. Harbulak and M. J. Albinak, Inorg. Synth., 1966, 8, 196.chap. 3.l°F. Basolo and R. Pearson, Mechanisms of Inorganic Reactions (Wiley, New York, 1958),l1 E. M. Hanna, A. D. Pethybridge, J. E. Prue and D. J. Spiers, J. Solution Chem., 1974, 3, 563.l2 K. N. Marsh and R. H. Stokes, Austral. J. Chem., 1964, 17,740.l3 W. A. Millen and D. W. Watts, J. Amer. Chem. SOC., 1967,249,6858.l4 J. E. Lind, J. J. Zwolenik and R. M. Fuoss, J. Amer. Chem. SOC., 1959, 81, 1559.l 5 Y. C. Chiu and R. M. FUOSS, J. Phys. Chem., 1968,72,4123.l6 A. D. Pethybridge and D. J. Spiers, Electroanalyt. Chem., in press.l7 D. J. Spiers, Ph.D. Thesis (Reading University, 1974).Is J. C. Bailar, Jr., and C. L. Rollinson, Inorg. Synth., 1946, 2, 222.l 9 G. Schwarzenbach, Helv. Chim. Acta, 1949, 32, 839.2o W. C. Duer, R. A. Robinson and R. G. Bates, J.C.S. Furaday I, 1972, 68, 716.21 A. D. Pethybridge and D. J. Spiers, Chem. Comm., 1974,423.22 M. G. Burnett, J. Chern. SOC. A , 1970, 2480, 2486,2490.23 Interatomic Distances (Chemical Society Special Publications, London, No. 11, 1958 ; No. 18,24R. A. Robinson and R. H. Stokes, Electrolyte Solutions (Butterworth, London, 2nd edn.25 P. J. Protzenko, 0. N. Shokina and N. P. Chekhunova, Russ. J. Phys. Chem., 1964, 38, 1013.1965).rev., 1959), (a) pp. 125 and 461 ; (b) p. 463.(PAPER 5/641

ISSN:0300-9599    

DOI:10.1039/F19767200064

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Conductance of some Cobalt(II1) Complexes in Water at 25°CPart 2.-Conductance of Salts of Ethylenediaminetetra-acetatocobaltate(111)BY ALAN D. PETHYBRIDGE* AND DAVID J. SPIERS?Department of Chemistry, The University, Whiteknights, Reading, Berks. RG6 2ADReceived 4th April, 1975Results are reported for the molar conductivities at 25°C of aqueous solutions of lithium, sodium,potassium and tetraethylammonium ethylenediaminetetra-acetatocobaltate(m). They are analysedin terms of the Pitts conductivity equation and are best considered as slightly associated with associa-tion constants in the order Li < Na < K > Et4N. A value of 26.17f 0.10 S cm2 mol-’ is reportedfor P ( [ C o (edta)]-).In the preceding paper we reported studies of the conductance of aqueoussolutions of salts of trans- and cis-[Co(en),(NO,),]+ and found a significant amountof outer-sphere complex formation for some of the salts.We now report an extensionof our conductance studies to aqueous solutions of salts containing the [Co(edta)]-ion to see whether the same factors influence the formation of outer-sphere complexesby anionic inner-sphere complexes. There was no problem of conductance drift withtime with solutions containing this anion. Measurements could therefore be madeby the more usual concentration-run technique in which successive weighed aliquotportions of a concentrated stock solution were added to the solution in the conductancecell.EXPERIMENTALThe apparatus and thermostat used have been described elsewhere,” as have the techniquesfor preparing the cell and conductivity water.3a Other experimental details were outlinedin the preceding paper.’PREPARATION OF COMPOUNDSConductivity water and materials of the highest quality grade conveniently available(usually AnalaR) were used throughout.Full details of the preparation and purificationof these salts are given elsewhere.4K[Co(edta)], E, was used as the starting material in the preparation of the other salts ofthis anion. Early attempts to follow the preparation recommended by Weakleim andHoard were not completely satisfactory so an alternative procedure was adopted. Allthe samples of K[Co(edta)] were prepared by the latter technique and were purified once bydissolving the product in the minimum quantity of water and filtering into three times thevolume of acetone, which was stirred continuously. The sample used for conductivitymeasurements was precipitated in this way twice more.The product was the dihydratewhich was stable in air. Although the salt could be dehydrated by heating under vacuumat 100°C, the anhydrous compound was hygroscopic and conductance runs were made withthe air-dried sample of the dihydrate. The solubility at room temperature is approximately1.3 moldm-3. Analysis for dihydrate: found C 28.3, H 3.8, N 6.7; calculated C 28.4H 3.8, N 6.6 %.t present address : International Nickel Ltd., European Research and Development Centre,Wiggin Street, Birmingham B16 O N .774 CONDUCTANCE OF CO"' COMPLEXESNa[Co(edta)] was prepared by passing 1 dm3 of a 0.05 mol d ~ n - ~ solution of E through acolumn of cation exchange resin Amberlite IR-120 (analytical grade) in the sodium form.800 cm3 of eluate were collected and evaporated down to 40 cm3, obtaining the crude productby pouring this into 300 cm3 of acetone.The salt was purified twice by dissolving in a smallquantity of water and filtering into excess AnalaR acetone. The product, the tetrahydrate,was stable in air and was used for the conductance measurements. The anhydrous saltcan be obtained by heating at 100°C under vacuum but it is hygroscopic. The solubility atroom temperature is approximately 0.6 rnol dmW3. Analysis for tetrahydrate : found C27.3, H 4.5, N 6.4; calculated C 27.2, H 4.6, N 6.3 %.Li[Co(edta)] was also prepared by ion exchange from a 0.05 mol dm--3 solution of E.The product was extracted from the eluate and purified in a manner similar to that for Na-[Co(edta)].The salt was precipitated as the trihydrate but drying in vacuo at 100°C producedthe anhydrous salt (not hygroscopic) which was used for the conductance measurements.The room temperature solubility was estimated to be 0.5 mol dm-3. Analysis : foundC 33.6, H 3.5, N 7.8; calculated C 33.9, H 3.4, N 7.9 %.Et4N[Co(edta)] was also prepared by ion exchange from a 0.05 mol dm3 solution of E.Addition of a large excess of acetone to the concentrated eluate produced a viscous purpleoil. The acetone was decanted off and after stirring with excess fresh acetone and leavingovernight a purple product was obtained.This was recrystallised from boiling ethanol, butthe product was extremely hygroscopic, forming a purple solution on a few minutes' exposureto the atmosphere. The purified salt was dried in vacuo at 60°C for 48 h and a specialtechnique was devised for preparing the stock solution. A sample of the salt was dried on avacuum line overnight and, after filling the line with dry nitrogen, was added rapidly to aweighed flask containing a known mass of conductivity water. The flask was reweighedto obtain the mass of salt added. Because of the hygroscopic nature of the salt no micro-analysis of the salt could be attempted, but as will be seen later, the value of Am obtained wasconsistent with independent single ion molar conductivities.The preparation and conductance results for ~rans-[Co(en)~(NO&][Co(edta)J are reportedin the preceding paper because the A values are time-dependent.RESULTS AND DISCUSSIONThe molar conductivities of the four salts are given in table 1.All conductivityvalues have been converted to absolute units.In the discussion the results for all runs on a given salt are analysed together togive a more realistic idea of the accuracy of the parameters obtained. For the analysisof any single run the value of the deviation function a,( %)l was usually less than 0.01.Our method of fitting the data and our reasons for choosing the Pins (P) equation '* *rather than the Fuoss-Hsia (FH) equation have been given e1sewhere.l.It is possible to fit the data for these salts quite satisfactorily by assuming themto be completely dissociated in aqueous solution.However, the values of the contactdistance a shown in table 2 are unreasonably low, decreasing in the order Li > Na > K.Consequently we have fitted the results by treating the salts as being slightly associatedin solution. In contrast with the data obtained in the preceding paper by the single-point technique, all the data for single runs and the combined data for Li[Co(edta)]show two points of statistical best fit, one at a low d, frequently with a negativeassociation constant KA, and the other at higher d and KA values. There is a closecorrelation between these best-fit d and KA values, regardless of the salt, shown in fig. 1.In our reanalysis of literature data we have frequently observed 2 * lo this type ofbehaviour and suspect it is often due to small systematic errors in measurements madeby the concentration-run technique.Such double minima are seldom reported, prob-ably because other computer programs either do not search over a sufficiently largerange of d values or stop when the first minimum is obtained. We consider lo thatone way of avoiding this problem when comparing KA values for different salts oA . D . PETHYBRIDGE AND D. J . SPIERS 75the same charge type and in the same solvent is to compare them at a common valueof d. A convenient value is d = 4, the Bjerrum critical distance, which is 3.58 A fora 1 : 1 electrolyte in water at 25°C and is close to the values of d found in those caseswhere a unique point of best fit is obtained. Similar results are obtained if any otherreasonable value of d is used, e.g., 24, although the absolute values of KA are, of course,altered.104 clmol dm-37.600 414.50820.03423.93028.1988.030 714.85419.86624.64928.6566.662 811.13115.52918.54021.014104 CITABLE 1 .-MOLAR CONDUCTIVITIES AT 25°CA / S cm2 mol-1 104 c/mol dm-3 A / S cm2 mol-1 104 c/mol dm-3Li[Co(edta)lU62.607 27.168 60.973 73.80361.901 37.378 60.406 134.4561.446 51.483 59.742 200.8061.181 66.522 59.151 292.1560.901 90.629 58.343 376.96Na[Co(edta)]"74.066 31.335 71.959 60.51473.337 52.673 70.835 104.8172.894 69.691 70.124 159.1172.545 92.817 69.299 232.0272.27 1 124.89 68.333 300.55K[Co(ed tallu97.528 22.198 95.526 67.42396.873 34.149 94.620 97.47396.375 41.071 94.215 126.3496.072 53.939 93.378 152.4695.843 74.970 92.322 221.5299.571 91.250 290.40Et4N[Co(edta)]A,!S cmz mol-158.86957.14755.75754.27653.21770.54268.96867.5 1965.98564.80992.59291.24190.14689.28687.33685.744mol dm-3 18.729 29.373 36.335 45.002 55.447 64.045 72.015 82.874mol-* 55.329 54.592 54.180 53.733 53.243 52.879 52.566 52.171A/S cm2a Three independent runs in different cells.TABLE 2.-PARAMETERS GIVING THE BEST FIT WITH THE P EQUATION ; SALTS TREATED AS FULLYDISSOCIATEDsalt a/A Am fS cm2 mol- b*( %ILi[Co(edta)] 3.01 64.662 0.04Et 4N[Co(edt a)] 1.61 58.440 0.01Na[ Co(edta)] 2.28 76.210 0.07K[Co(edta)] 0.75 99.614 0.09TABLE 3.-PARAMETERS GIVING THE BEST FIT WITH THE P EQUATION WITH d = 4 ; SALTSTREATED AS ASSOCIATEDsalt Am/S cm2 mol-1 K*/dm3 mol- ' U K ~ @A( %) Am(Cco(edta)l-)Li[Co(edta)] 64.661 0.30 0.29 0.04 26.00Na[Co(edt a)] 76.217 0.67 0.25 0.06 26.14K[Co(ed t a)] 99.675 1.69 0.37 0.07 26.21Et4N[Co(edta)] 58.449 1.20 0.04 0.01 26.31Table 3 shows the parameters which give a best fit for the combined data for eachsalt when d is set equal to q.The association constants obtained from analysis ofsingle runs usually lie within a standard deviation of the KA value calculated for acombined run, unless the runs cover very different concentration ranges. Even so76 CONDUCTANCE OF CO"' COMPLEXESboth the P and FH equations give association constants for the [Co(edta)]- salts inthe order Li < Na c K > Et,N, although the values obtained from the FH equationare consistently 0.2 mol dm-3 lower than those in table 3.As discussed in the preced-ing paper the salt trans-[Co(en),(NO,),][Co(edta)] is quite strongly associated butas the A" value obtained is some 9 units too high not much reliance can be placedon the absolute value (8 dm3 mol-l at d = 4 for the P equation).If the values of KA at d = q are plotted against the sum of the crystallographicradii (fig. 2), the present salts fit in with the trend recorded in the previous paper,4t 0I2 xb2035 LA8X C0 223 x0 j-:, , , , , , ,-200 4 8 12 16dlAFXG. 1.-Values of KA and d giving statistical best fit of individual and combined runs using the Pequation.Numbers refer to individual runs, c denotes combined data. Salts are , 0 Li[Co (edta)],x Na[Co (edta)], A K[Co (edta)] and 0 Et4N[Co (edta)].although Na and Li fall slightly below the values for other salts. We note that anycorrelation of KA appears to be with the crystallographic radius of the anhydrouscation rather than the hydrodynamic radius of the solvated species. This seems toindicate that the solvating water is displaced when the cation and the [Co(edta)]-anion associate to form a non-conducting species.The deviation of Et,N[Co(edta)] is particularly marked, but unfortunately onlyone successful run was made with this salt as the experimental difficulties were greatowing to its extremely hygroscopic character.The low value Of KA for Et4N[Co(edta)]may well be due to the structure of the water round the two ions being so dissimilar thatthere is a kinetic barrier to the formation of a non-conducting outer-sphere complex.If this were so a study of the tetra-alkylammonium fluorides might be expected toshow similar results. For analysis with d = 2q the points are raised by about1 dm3 mol-1 and the order of association constants is Li < Na < K % Et4N.and ourrecommended value 3b for A"(Et,N+) = 32.13 S cm2 mo1-I with the An., values reportedin table 3 the values of A"([Co(edta)]-) in the last column are obtained. The meanvalue is 26.16f0.10 S cm2 mol-1 compared with the mean value for trans- and cis-[Co(en),(NO,),]+ of 27.45 * 0.3 S cm2 mol-l. A simple calculation using knownBy combining the published values of A"(M+) for the alkali metal ionA.D. PETHYBRIDGE AND D. J . SPIERS3+A+ A+AKE-A + ++0 + .*X A-NaEX 2"A-LiEEt4N E /I x x * x 0I I I 10 2 4 6 877&,s*lAFIG. 2.-Plot of KA values at d = q using the P equation, against the sum of the crystallographicradii of the ions. x alkali metal halides, 0 alkali metal oxosalts, + tetra-alkylammonium halides, A trans- and cis-[Co (en)2(N02)2]+ salts, salts of [Co (edta)]-.interatomic distances l 2 and angles and van der Waals radii l 3 shows that both ionshave a radius of 4.3 A.There is probably some slight hydrolysis of the [Co(edta)]- anion according to thescheme l4[Co(edta)]- f [Co(edta)(H,O)]- + [Co(edta)(OH)I2- + H+and definite evidence of similar behaviour with Cul* and several multidentate ligandshas been established by n.m.r.spectros~opy.~~ The pH of a 0.010 0 mol dm-3 solu-tion of K[Co(edta)] was 6.2 and in the preceding paper we ascribed the increased rateof aquation of the cation in trans-[Co(en),(NO,),][Co(edta)] to the hydrogen ionsproduced by the hydrolysis of this anion. From the point of view of the conductancemeasurements reported in this paper however, this hydrolysis is not important becausethe equilibrium concentration of the products on the extreme right-hand side is onlyabout 0.01 % of the total concentration of the [Co(edta)]- ion.Note added in proof. We have reanalysed our data using the latest Fuoss equation (J.Phys. Chem.,1975, 79, 525). The new equation with d = q yields ha values 0.04 S cm2 mo1-1 larger than thosefrom the P equation in table 3 but KA values 0.2, 0.4,0.6 and 0.4 dm3 mol-I lower for the Li, Na, Kand Et4N salts respectively.One of us (D. J. S . ) thanks the S.R.C. and the University of Reading for financialsupport.A. D. Pethybridge and D. J. Spiers, J.C.S. Furaduy I, 1976, 72, 64.E. M. Hanna, A. D. Pethybridge, J. E. Prue and D. J. Spiers, J, Solution Chem., 1974, 3, 563.A. D. Pethybridge and D. J. Spiers, (a) J. Electroanulyt. Chem., in press ; (b) to be published.H. A. Weakleim and J. L. Hoard, J. Amer. Chem. SOC., 1959, 81, 549.* D. J. Spiers, Ph.D. Thesis (Reading University, 1974)78 CONDUCTANCE OF CO"' COMPLEXESF.E.E.R.P. Dwyer, E. C. Gyarfas and D. P. Mellor, J. Phys. Chem., 1955,59,296.Pitts, Proc. Roy. SOC. A, 1953, 217, 43.Pitts, B. E. Tabor and J. Daly, Tram. Furachy SOC., 1969,65,849.M. Fuoss and K.-L. Hsia, Proc. Nat. Acud. Sci. U.S.A., 1967, 57, 1550 ; 1968, 58, 1818.l o A. D. Pethybridge and D. J. Spiers, Chem. Comni., 1974, 423.R. A. Robinson and R. H. Stokes, Electrolyte Solutions (Butterworth, London, 2nd edn. rev.,1959), p. 463.l 2 Interatomic Distances (Chemical Society Special Publications, London, No. 11, 1958; No. 18,1965).L. Pauling, % Nature of the Chemical Bond (Cornell University Press, 1940), chap. 10.l4 G. Schwarzenbach, Helv. Chim. Acta, 1949, 32, 839.F. J. C. Rossotti, K. B. Dillon, M. R. Harrison, D. J. Spiers and H. R. Sunshine, unpublishedwork.(PAPER 5/642

ISSN:0300-9599    

DOI:10.1039/F19767200073

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Conductance of Tetra-alkylammonium Perchlorates inAcetonitrile+Methanol Mixtures at 25°CBY ALESSANDRO D'APRANO, MARIO GOFFREDI* AND ROBERTO TRIOLOInstitute of Physical Chemistry, University of Palermo,Via Archirafi 26, 90123 Palermo, ItalyReceived 14th April, 1975The association and the hydrodynamic behaviour of some quaternary ammonium perchloratesin acetonitrile+ methanol mixtures have been investigated by precise conductance measurements at25°C. The dependencies of association and mobility on solvent composition are primarily due tocation size and specific short-range ion-solvent interactions.It is we1 established that the extent of association of a series of electrolytes indifferent solvea ts is specific for any ion-solvent combination, rather than being di-electric constant dependent.The association behaviour of alkali metal and quater-nary ammonium perchlorates in an aprotic solvent such as acetonitrile and a proticsolvent such as methanol is just one examp1e.l This paper extends the measurementsto some tetra-alkylammonium perchlorates in the approximatively isodielectric solventmixture acetonitrile + methanol, with a view to obtaining information on the effectof short-range interactions between ions and adjacent solvent molecules on the ion-pairing process.EXPERIMENTALTetramethylammonium (Me4NC104), tetraethylammonium (Et4NC104), tetrabutyl-ammonium (Bu4NC104) and tetrahexylammonium perchlorates (Hex4NC104) wereprepared, purified and dried as reported previously. Methanol and acetonitrile were purifiedas already de~cribed.~The Pyrex conductance cells were of the Erlenmeyer type as described by Daggett, Bairand Kraus5 with bright platinum electrodes.The cell constants were determined at25.000+0.002"C by the method of Lind, Zwolenick and FuossP All the conductance runswere carried out by the concentration method and the measured resistances were correctedfor the usual frequency dependence. The bridge has been described elsewhere.'All solutions were prepared by weight, vacuum corrected and volume concentrations inequivalents per litre were calculated using the density of the solvents. Solvent mixtures werealso made up by weight; their properties, interpolated from literature data,8 are given intable 1,* where w is the weight % of methanol, d is the density, q is the viscosity and D thedielectric constant.RESULTS AND DISCUSSIONThe measured equivalent conductances A(ohm-l equiv.-l cm2) at correspondingconcentration c(equiv.dm-3) are summarized in table 2, where each set of data isidentified by reference to the corresponding dielectric constant value of the solventmixture.* Tables are collected in an Appendix.780 CONDUCTANCE OF TETRA-ALKY LAMMONIUM PERCHLORATESThe conductance data were analysed by means of eqn (1)A = A0 - SJCY + ECY log CY + J c ~ + JZcsyt- KAcyf 2A (1)where the symbols have their usual significance. The parameters Ao, KAY a and thestandard deviation percent (a/ho)lOO obtained by a computer analysis are given intable 3 together with the Walden products A0q. In fig.1, log& vs. 1/D plots areshown for all the tetra-alkylammonium salts here analysed. Note that log& decreasesmonotonically from pure methanol to pure acetonitrile when Hex4NC104, Bu4NC104and Et4NC104 are considered. Moreover, a minimum appears in the acetonitrile-rich region for Me4NC104 as already found for KC104 lo in the same mixtures.2.00 2.90 3 . 0 0 3.1ClOO/DFIG. l.-LOg& variation as a function of dielectric constant for (0) Me4NC104 ; ( 8 ) Et4NC104 ;(a) Bu4NC104 and (0) Hex4NC104 in acetonitrile + methanol nlixtures at 25°C.The non-linearity of log& plotted as a function of 1/D and the fact that for allthe salts the curves lie above the theoretical straight line of eqn (2) l1e 2bkDTlo@, = logKi + - (2)suggest the existence of strong interactions between the solvent and the electrolyte.As was earlier pointed out,' the different degree of ion-pairing found for thesequaternary ammonium perchlorates in pure methanol and pure acetonitrile can berationalized in terms of a two-step mechanism involving solvent-separated andcontact-solvated ion-pairs,l2 or in other words, the excess of association of a saltin the two solvents is strictly dependent on the contributions of two terms relatedboth to ion-solvent and ion-pair-solvent interactions.As a consequence, by adding acetonitrile to a methanolic solution of a salt inwhich only the anion can be solvated by the protic solvent, we would expect a decreaseof the association extent.If, on the other hand, only cation solvation (by the proticsolvent) occurs we would expect an increase of association. When both cation andanion can be solvated they will exhibit compensating effects, that is to say, a minimumin the log& vs.1 / D plot might appearReturning to the present results, we note that this is the case for Me4NC104A . D’APRANO, M. GOFFREDI AND R. TRIOLO 81while for the other three salts, whose cations are poorly or not solvated at all, theonly effect observed is the one related to anion solvation.Mobility data for these electrolytes are shown in fig. 2 where the Walden productsare plotted against the mole fraction of methanol in the mixtures. The salts showa nearly parallel behaviour in the small variation of Aoq over all the solvent composi-tion range.Furthermore, all sets of data show a systematic deviation from thesmooth curve for 0.70 < XMeOH < 0.90, suggesting a common origin. Such beha-viour seems to be related to the change in the structure of the solvent mixture asshown by the negative deviation of the molar volume excess plotted in the same figure.Present knowledge of the structure of these solvents, however, is not detailed enoughto permit a direct correlation of the hydrodynamic and associative behaviour of thesesolutions.A L - 0 0.25 0 . 5 0 0.75 1.0x2FIG. 2.-Walden product dependence on mole fraction of methanol (X2) for (0) Me4NC104 ;( 0 ) Et4NC104 ; (a) Bu4NC104 and (a) Hex4NC104 (ordinates right). The molar volume excess inper cent (Av/v) x 100 (-.-.-.) against mole fraction of methanol (Xz) (ordinates left).wt.% methanol0.0014.4923.9933.7050.0050.5051.4059.7660.1069.2273.8074.2082.6085.9789.8390.00100.00APPENDIXTABLE PROPERTIES OF SOLVENT MIXTURES AT 25°C3.448 0.776 903.340 0.779 323.350 0.780 663.430 0.782 043.663 0.784 223.672 0.784 283.686 0.784 383.848 0.785 393.854 0.785 434.190 0.786 384.308 0.786 714.316 0.786 924.586 0.787 004.720 0.786 994.880 0.786 964.891 0.786 955.450 0.786 55103 ~ I P d/g ml-1 D36.0235.5235.2034.7634.3234.3134.2834.0033.9833.6733.5233.5133.2233.1032.9832.9732.682 CONDUCTANCE OF TETRA-ALKYLAMMONIUM PERCHLORATESTABLE 2.-EQUIVALENT CONDUCTANCES OF TETRA-ALKYLAMMONIUM PERCHLORATES IN ACETO-NITRILE+ METHANOL MIXTURES AT 25°CD35.5234.2833.6735.5234.7634.2833.6733.22l04c/equiv. dm-3 A/cmz R-1 equiv.-I D3.11405.592 28.524 411.36914.2823.393 68.807 912.54315.76018.6713.907 86.920 613.83217.31721.0934.729 78.229 515.96119.54723.1804.120 87.941 711.53615.1 1618.3924.251 08.586 613.39316.83921.03024.4534.670 38.392 812.42915.58618.87821.9289.650 513.73 118.22422.02525.354Me4NC104199.77 34.76197.08194.55192.52190.65186.57 33.98181.34178.71176.74175.13169.85 33.22166.89161 -92159.98158.04Et4NC104187.86185.02180.47178.84177.35184.28180.99178.64176.66175.08173.64170.12167.23165.48163.58162.24158.34155.34152.87151.23149.68148.41140.36138.01135.74134.15132.9135.2034.3133.9833.5132.98104c/equiv. dm-3 A/cm2 R-1 equiv.-I8.577 86.890 09.934 614.04018.0372.884 75.536 18.842 214.97018.8293.331 86.328 99.234 912.39316.25319.1734.560 69.509 213.00417.11220.2505.889 79.645 713.90217.6482 1 A5227.9095.878 211.51116.59621.12525.18629.8596.859 810.70215.18619.36823.5976.691 010.43714.41518.10126.250196.82193.46191.03188.35186.12180.36177.38174.44170.301 68.08155.91152.90150.51148.36146.06144.54187.51183.54181.41179.35177.90173.21170.45167.96166.12164.47162.03165.27161.26158.61156.50154.91153.31151.43148.79146.32144.37142.63134.68132.08129.79127.96124.5A .D’APRANO, M. GOFFREDI AND R . TRIOLO 83D35.5234.2833.6733.2235.2033.5233.10104c/equiv. dm-32.541 65.233 37.992 010.76713.19315.8372.661 75.256 37.766 610.66913.49416.6664.593 98.439 111.88715.26618.00221.1743.330 27.766 710.71013.98216.64919.4642.644 66.268 810.13214.11819.13622.2632.624 46.100 59.792 713.98722.1002.947 06.296 510.55015.36420.32826.207TABLE 2.-continuedBu4NC104165.35 35.20162.79160.80159.16157.94156.75150.27 34.00147.88146.10144.40143.01141.63134.18 33.51131.54129.69128.14127.01125.85122.46 32.98119.12117.46115.88114.62113.61Hex4NC104153.44 34.32150.32147.91146.02144.04142.96122.82 33.22120.00117.88115.93112.95111.43 32.97108.82106.41104.24102.36100.45104c/quiv. dm-33.259 95.901 27.763 110.52113.48616.0054.261 27.325 910.62713.86016.91520.6605.210 113.30516.37220.64424.6822.592 35.976 58.912 612.12115.85219.1 142.599 66.380 710.44814.95019.99925.3622.563 65.719 09.437 113.23622.8763.163 96.937 811.84416.62922.25328.826163.49161.15159.90158.20156.70155.55142.05139.76137.84136.26134.96133.52129.28124.58123.24121.59120.21115.42112.52110.63108.89107.17105.85141.27138.08135.73133.73131.81130.081 15.02112.43110.21108.38104.78107.30104.48101.7999.6997.6495.584 CONDUCTANCE OF TETRA-ALKYLAMMONIUM PERCHLORATESTABLE 3 .-DERIVED CONSTANTS FOR TETRA-ALKYLAMMOWM PERCHLORATES IN ACETOMTRILE+METHANOL MIXTURES AT 25°CD35.5234.7634.2833.9833.6733.2235.5235.2034.7634.3 134.2833.9833.6733.5133.2232.9835.5235.2034.2834.0033.6733.5133,2232,9835.2034.3233.5233.2233.1032.97207.42+0.010205.0Sk 0.004194.44& 0.005187.52+0.0101 77.89 & 0.01 0163.OOf0.010196.77_+0.010196.34$-0.0201 92.59 0 .O 1 0182.88k 0.004181.82+0.010174.76& 0.030166.46+0.010161.30f0.010151.93f0.020144.15+ 0.002171.36& 0.040170.32+ 0.007156.13k 0.003149.30+ 0.003141.44f0.002136.94_+0.001128.37+0.010120.4640.003159.37f0.010146.85+_ 0.010127.95rt:0.003119.95f0.010116.69f0.003112,73 & 0.002&/dm3 mol-1Me4NC10418.61 f 0.0519.96f 0.0524.84+ 0.0328.24f 0.0630.60f 0.0536.92f 0.04E t4NC10414.16+ 0.0415.02+ 0.0815.63k0.051 8.12f 0.0218.45 + 0.0521.45 + 0.1024.20f 0.0626.62+ 0.0430.52+ 0.0936.95 5 0.01Bu4NClOd11.66f 0.0312.11_+0.0515.8950.0317.83+ 0.0221.46k0.0223.94+ 0.0529.22$- 0.1035.6850.03Hex,NClQ411.20+ 0.0614.17f 0.0722.33f 0.0327.92+ 0.0130.92+ 0.0335.56k0.024.94.94.44.14.03.76.06.06.05.65.65.14.84.54.23.76.96.96.25.95.34.94.33.97.26.75.24.54.23.90.0100.0050.0070.0100.0100.0100.0100.0200.0100.0040.01 00.0300.0100.0100.0300.0050.0080.0100.0080.0060.0050.0020.0300.0100.0200.0200.0100.0030.0100.007AoVlcrn2 9-requiv.-1 P0.6930.7030.7170.7220.7450.7480.6570.6580.6610.6710.6710.6750.6970.6970.6970.7030.5720.57 10.5760.5750.5930.5920.5890.5880.5340.5380.5510.5500.5510.551A. D’Aprano, M.Goffredi and R. Triolo, J.C.S. Fumduy I, 1975, 71, 1188.F. Accascina, M. Goffredi and R. Triolo, 2. phys. Chem., 1972,81, 148.F. Butera, M. Goffredi and R. Triolo, Atti Accad. Sci. Lett. Arti, 1966-67, 27, 191.M, Goffredi and R. Triolo, J.C.S. Firuduy I, 1972, 68, 2324.H. M. Dagget, B. J. Bair and C. A. Kraus, J. Amer. Chem. SOC., 1951, 73,799.J. E. Lind, Jr., J. J. Zwolenick and R. M. Fuoss, J. Amer. Chem. Soc., 1959, 81, 1557.M. A. Coplan and R. M. Fuoss, J. Phys. Chem., 1964, 68, 1181.A. D’Aprano, J. Phys. Chem., 1971, 75, 3290.lo A. D’Aprano and I. D. Donato, J.C.S. Furaduy I, 1973, 69, 1685.l 1 R. M. Fuoss, J. Amer. Chem. SOC., 1958,80, 5059.l 2 D. F. Evans and P. Gardam, J. Phys. Chem., 1969,73, 158.’ F. Accascina, A. D’Aprano and R. M. Fuoss, J. Amer. Chem. Soc., 1959, 81, 1058

ISSN:0300-9599    

DOI:10.1039/F19767200079

出版商:RSC    

年代:1976

数据来源: RSC

摘要:

Chain Initiation of Neopentane Pyrolysis and a SuggestedReconciliation of the Thermochemically Calculated andMeasured Rate Constants for the Recombinationof t-Butyl RadicalsBY ROGER M. MARSHALL,* HOWARD PURNELL AND PETER D. STOREYDepartment of Chemistry, University College of Swansea, Singleton Park,Swansea SA2 8PPReceived 15th April, 1975The rates of initiation of neopentane pyrolysis over the temperature range 756-845 K have beenmeasured at reactant pressures in the range 100-200 Torr, by processing of data relating to the forma-tion of the termination product, ethane, using an exact algebraic procedure. Thus, the data are freeof the ambiguities introduced by the empirical extrapolation procedures used in previous directdeterminations of the initial rates and the derived Arrhenius parameters ofneo-CSH12 -+ CH3 + t-C4H,. (1)The result obtained islog (k,/s-l) = 16.1 k 1.0-(3302 15 kJ mol-')/2.303RT.Values of kl are in agreement with previously measured values but the Arrhenius parameters areinconsistent with the presently accepted thermochemistry of reaction (1).A modified thermochemistryfor the t-butyl radical is proposed leaving the heat capacity unchanged but using the new values for298 K,AHfjkJ mol-I = 39, S(l mol c ~ - ~ ) / J mol-I K-I = 210.8.These, and the presently derived k , values allow the calculation for 800 K oflog (k-,/cm3 mol-I s-l) = 12.9with essentially zero activation energy and hence, via the geometric mean rule, lead tolog (k9/cm3 mol-l s-l) = 11.9for the mutual recombination reaction,2t-C4H, --f 2,2,3,3-tetramethylbutane.(9)The new thermochemistry suggested for t-butyl reconciles most thermochemically calculated valuesof k9 with directly measured values over a wide temperature range. However, further experimentaland theoretical justification is necessary before the new thermochemistry can be unequivocally accepted.log (k3k6/ks/cm3 mol-' s-l) = 13.2+ 1.5-(1275 12 kJ mol-')/2.303RTConcurrently evaluated with kl is the resultCH3 + neo-C5H1, + CH4 + C5H1CH3 + i-C4Hs --f CH4 + C4H7(3)(6)2CH3 -+ CZH6 (5)which is shown to be in excellent agreement with that calculated from the independent results ofother workers.886 NEOPENTANE PYROLYSISThere appears to be no dispute that the mechanism of the initial stages of neo-pentane pyrolysis isC5H12 + t-C,H,+CH, (1)t-C,H, + i-C4H8 + H ( 2 4H+CSHIZ + Hz+CSH11 (2b)(3)C5H1 + i-C4H8 + CH3 (4)2CH3 + C2H6 (5)(6)(7)(8)CH3 + C5H12 + CH4 + CsH11CH, + i-C4H8 + CH4 + C4H7CH3+C4H7 + CsHlo or CH4+C4H62C4H7 -+ C8H14 Or C ~ H G 4- C4H8.Two detailed analytical studies * established the general, mechanistic featuresof the reaction and differed in interpretation only on points of detail.Both groupsof workers attempted to evaluate the Arrhenius parameters, Al and El, of reaction (1)by measurement of the trivial yields of hydrogen. The raw data were in close accordbut differences in interpretation, although minor, led to somewhat different Arrheniusparameters. Our previous study also included measurement of ethane yields whichcould also be employed to estimate A l and El with results which were compatiblewith those based on the hydrogen yield data.However, in both studies, the earlyonset and substantial magnitude of self-inhibition introduced uncertainty since curve-fitting procedures designed to give initial reaction rates were necessitated, the basesof which were purely empirical.The results obtained for the approximate temperature range, 713-823 K, werelog(A,/s-') = 18.05, E,/W mol-' = 359 ;andlog(A,/s-l) = 16.8, E,/kJmol-' = 343.*However a shock tube study in the range, 1070-1240 K, had yielded significantlydifferent values, the recently slightly revised figures beinglog(A,/s-l) = 16.2, E,/kJmol-l = 326.Subsequently, Pacey has carried out a study in the intermediate temperature range,793-953 K, and obtained the resultslog(A,/s-') = 17.7, E,/kJmol-l = 356.We have restudied the reaction using a more sensitive analytical system and adopt-ing a more acceptable method of data-processing which does not involve any graphicalcurve-fitting procedures. In essence, we have treated the above mechanism in itsentirety and derived the explicit equation for the yield of ethane as a function of timeof reaction. The derivation is outlined below.A steady-state treatment of the mechanism consisting of reactions (1) to (8),making the usual assumption of long chains and also assuming that k? = 4ksk8,gives the resulR .M . MARSHALL, H . PURNELL A N D P . D. STOREYClearly, d[CH,],/dt = k,[CH,],[C,H,,J and, since [i-C4H8], = [CH,],,87This may be directly integrated since, at the low conversions used, [C5H12] is effectivelyconstant in any one experiment, hence,Also, from the steady state treatment,dCC2H6" = k,[CH,]: = kl[CSHI2]dtExpansion of the denominator and subsequent substitution of eqn (I) then givesHence.by integration,where a = (k3k6/k5).The principle of the data processing method is to find the value of a which makesa plot of [C,H,], against log,(l+a[C5Hl,]t) a straight line, common for all initialpressures of neopentane at a fixed temperature, passing through the origin. Theproduct of the slope of this line and a then gives a value of k l . In practice, measuredvalues of [C2H6]? as a function of t and of [C5H12], at a fixed temperature, wereprocessed by computer using a suitably chosen range of values of a.For each valueof a, a least squares line was calculated, and hence, the value of a providing zerointercept was eventually evaluated.[C,H61, = (Wa) lo,oe(l +aLHl2lt) (11)EXPERIMENTALPhillips research grade (99.99 %) neopentane, in which n-butane was the only impuritydetectable, was used. The neopentane was thoroughly outgassed at the temperature of anisopentane/liquid nitrogen mixture.The pyrolysis was studied in a clean quartz reaction vessel in a conventional static reactionsystem operated at temperatures within the range, 756-845 K. The details have beendescribed elsewhere.6 Initial reactant pressures ranged between 100 and 200 Torr.The analytical problem was not simple since ethane was present only in amounts in theorder of Torr and this, in presence of a two-thousand-fold excess of methane.Thus,because of overlap of these two peaks, a much better than usual resolution of these substanceswas demanded. This in turn reduced ethane peak heights and increased the need for highdetector sensitivity. An 80 x 0.45 cm stainless steel column containing 2 % (w/w) silicone oilon 100/120 mesh (A.S.T.M.) alumina provided the separation and a modern flame detectorthe sensitivity. The column was operated at 329 K at a nitrogen flow rate of 15.3 cm3 min-l.RESULTSDetailed measurements of ethane yields as a function of time were carried out ateach of eight temperatures at up to five initial pressures of neopentane.Fig. 1 showsa plot of the data, for reactions at 766 K and five initial pressures plotted accordingto eqn (11) with the value log(a/cm3 mol-l s-l) = 4.60, which leads to zero interceptof the least squares line which is shown. The results for all temperatures ar88 NEOPENTANE PYROLYSISsuminarised in table 1 where we list the corresponding values of a( = kdk3/kJ and thederived values of k l . The Arrhenius parameters calculated by least squares analysisof these data are :log(A,/s-l) = 16.1 & 1.0, EJkJ mol-1 = 330+ 15 ;log(A,/cm3 mol-1 s-l) = 13.2f 1.5, E,/kJ mol-1 = 127f 12where the error limits quoted are 95 % confidence limits.,+0UI I I I0 0 . 5 I .o I .5 2 .o 010g(l +a[C5H121t)FIG. 1.-Data for 766 K plotted according to eqn (11) with log (a/cm3 md-' s-') = 4.60.Initialpressures/Torr: 0,120; a, 145; 0,160; A, 180; 0,200.TABLE 1 .-EXPERIMENTAL VALUEStemperature/K 756 766 784 794 795 806 826 845log (Ws-l) -6.72 -6.41 -5.91 -5.72 -5.52 -5.27 -4.81 -4.32log(a/cm3 mo1-I s-') 4.42 4.60 4.70 4.95 4.79 4.82 5.22 5.34DISCUSSIONThe presently derived Arrhenius parameters for reaction (1) are in obvious dis-agreement with those of other workers determined in similar temperature ranges.Nevertheless, the actual values of k , measured in the present work are in excellentagreement with the actual measured values of other workers. It is only in theapportionment of the rate constant between A l and El in which the discrepanciesoccur. Since we feel that the data-processing techniques used in our present workare superior to those used in earlier work, we believe that the presently derived valuesof A l and El are the most reliable in the temperature range around 800 K.The currently accepted thermochemistry for reaction (1) which is based on directmeasurements for the alkane involved ' and on a combination of experimental resultsand group additivity principles * for the free radicals, yields the results for 800 KAUl/kJ mol-l = 321 and AS1/J mol-' K-l = 89.R.M . MARSHALL, H . PURNELL AND P . D. STOREY 89where AUl is the internal energy change and ASl the entropy change for a standardstate 1 mol ~ r n - ~ . Thus, using the equationsEl -El = AUl and log(A,/A-,) = (AS1 -R)/(2.303 R)we calculate from our Arrhenius parameters for reaction (1)E-JkJ mol-1 = 9 and log(A-,/cm3 mol-l s-l) = 11.9.It is almost universally believed that radical recombination reactions proceed withzero activation energy and therefore the origin in our calculation of a small activationenergy merits close attention. There are two obvious sources.First it could be dueto experimental error in our measured values of kl and indeed the 95 % confidencelimits on our value of El( k 15 kJ mol-l) do provide an adequate explanation for thenon-zero value of E- l . However, for reasons which are more fully explained below,we reject this, albeit perfectly acceptable, explanation in favour of the second alterna-tive, namely an error in the thermochemistry used. Since it is almost inconceivablethat there could be an error in the thermochemistry of neopentane, we must lookclosely at the thermochemistry of methyl and of t-butyl. The values for methyl seemto be very well founded and no serious discrepancy exists between the thermo-dynamically calculated value of the equilibrium constant forand the kinetically determined one based on the measured values of the forwardand reverse rate constants.Thus, if thermochemical error exists it is most probablethat it is in the values for t-butyl. There are three factors to consider here, namelythe heat capacity as a function of temperature, the heat of formation at 298 K andthe entropy at 298 K. It seems impossible that the heat capacity could be so muchin error as to account for the discrepancy and so we reject this and concentrate onthe values at 298 K of the heat of formation and of the entropy.The value of AHf used up to this point is the group additivity value, 28 kJ mol-l.Published values based on iodination studies are,l0 32k5 and 34-F 5 kJ mol-l, i.e.somewhat higher.Thus, if we were to use the value 37 kJ rnol-l, we would still beconsistent with these measured values and, moreover, we would have eliminated theapparent activation energy far reaction ( - 1). We propose however, for reasonswhich will become apparent below, to proceed using the value 39 kJ mob1 which isstill in reasonable agreement with the measured values and also permits the calculationof essentially zero activation energy for reaction (- 1).It has been suggested by Choo, Beadle, Piszkiewicz and Golden l2 that the entropyat 298 K of t-butyl has been overestimated by an amount R log,8 due to an incorrectassignment of the symmetry number.If this view is correct, then an unfortunateerror has been made not only by the compilers of the group additivity tables 13 butalso by ourselves,' since an error of this magnitude has very profound effects. Weproceed on the assumption that R log,8( = 17.3 J mol-1 IS-l) is to be subtracted fromthe presently accepted value of the entropy of t-butyl at all temperatures.Making the appropriate adjustments due to the above suggested changes in theheat of formation and entropy of t-butyl leads to the revised thermochemical valuesshown in table 2. Then, using these results we calculate, from our data, for therecombination of methyl with t-butyl the rate constant log(k- Jcm3 mol-1 s-l) = 12.9with effectively zero activation energy.The results for k , of all other groups of workers infer, using the data of table 2,a finite activation energy for reaction ( - 1) in the range 5 to 26 kJ mol-' .We suggestthat these values are artefacts arising from wrong apportionments of the measuredrate constants, kl, between A, and El and that the best estimate of k- from theseC2Hs +2CH90 NEOPENTANE PYROLYSISresults is obtained by calculating kl for the mean temperature of each group ofworkers and calculating k- from it using appropriate values interpolated from table 2.Values of log(k,,/cm3 mol-1 s-l) calculated in this way for the various groups ofworkers are : Halstead et aL,l 12.9 at 768 K ; Baronnet et aZ.,2 12.7 at 763 K ; P a ~ e y , ~12.9 at 873 K ; and T~ang,~* 13.2 at 1 I55 K.Clearly, except for the results calculatedfrom the data of Tsang and of Baronnet et al. there is very satisfactory agreementwith the value derived from our present results. Since the two discrepant resultsdiffer from the others only by a factor of two, it is with some confidence that we cannow propose that the best present estimate is10g(k-~/cm~ mol-' s-l) = 12.9.The geometric mean rule, k i ~ = 4kAAkBB, relating the rate constants of recombina-tion of radicals A with B, A with A and B with B is of proved validity for manypairs of radicals, including methyl and t-butyl, over wide temperature ranges.3-1Thus, using the long accepted value, log(k,/cm3 mol-'s-l) = 13.3 for the rate ofrecombination of two methyl radicals we may calculate the rate constant for therecombination of two t-butyl radicalsto be given by log(k9/cm3 mol-' s-') = 11.9.2t-C4H, -+ 2,2,3,3-tetramethylbutane (9)TABLE 2.-REVISED THERMOCHEMICAL VALUEStemperature/K 700 800 900 1000 1100 1200AUl/kJ mot1 335 332 329 326 323 320AS, /J mol-l K-' 76.5 72.4 68.8 65.7 62.8 60.1log(A1IA-d 3.6 3.3 3.2 3 .O 2.8 2.7This rate constant has been measured directly by several workers, the most recent(logarithmic) values being 11.7 by Choo et a l l 2 at 650 K, 12.1 by Parkes and Quinn l6at 298 K, -12 by Batt,,' - 11.5 by Golden et aZ.18 at -620 K and - 12 by Grillerand Ingold l9 in solution at 298 K.Clearly, there is very satisfactory agreementamong these and with the above calculation. Values have also been obtained withthe use of the currently accepted thermochemistry of t-butyl by three groups ofworkers. We now recalculate these using the modified thermochemistry proposedhere for t-butyl. In this way the (logarithmic) values obtained are 12.0 at 373 Kfrom Hiatt and Benson,20 11.9 at 462 K from McMillen, Golden and Benson 21(incidentally, in these two papers Benson et al. use the value 33 kJ mol-1 for theheat of formation of t-butyl at 298 K) and 13.7 at 500 K from our previous work.22We regard this last result as very unreliable since it is the end result of long extra-polations of two independent measurements and thus we will reject it in any furtherdiscussion.Clearly, the suggested modifications to the thermochemistry of t-butyl provideessentially total reconciliation between the directly measured and thermochemicallycalculated values of k9 as well as reconciling the majority of data for k- ,.Never-theless, before the new thermochemistry can be unequivocally accepted, new experi-mental determinations of the heat of formation of t-butyl must be shown to be inagreement with the present postulation and furthermore the theoretical and practicalimplications of the proposed entropy of t-butyl will have to be considered.One further value of the rate constant, k9, may be calculated using the modifiedthermochemistry proposed earlier for t-butyl.on theshock-tube pyrolysis of 2,2,3,3-tetramethylbutane the (logarithmic) value obtained isFrom the results of TsanR . M . MARSHALL, H. PURNELL A N D P . D . STOREY 9113.0 at 1063 K, a high value in line with the correspondingly high value obtainedfor k,l from the results of Tsang already dealt with. Furthermore, the value E9/kJ mol-1 = 25 is obtained. This result for k9 is irreconcilable with the other valuesquoted without resorting to drastic changes in our view of the thermochemistry oft-butyl ; basically we would have to leave the presently suggested thermochemistryup to -900 K unchanged, to preserve the reconciliation already achieved, and topropose sudden substantial change in the heat capacity in the range 900-1200 K toreduce the apparent value of k9.Since the change in heat capacity required is atleast 50 %, such a procedure is wholly unacceptable. These results of Tsang dotherefore stand alone in disagreement with those of other workers.The other function evaluated concurrently with kl in this work is the ratioa( = k3k6/kS) and our results may be compared with values calculated from literaturedata. Pacey has determined directly the rate of constant ratio10g(k~k~/crn~*~ mol-* s-*) = 6.8 -(67 kJ m01-~/2.303 RT)albeit in a slightly higher, though overlapping, temperature range. Konar et aZ.22determined the ratioin the same temperature range by making reasonable assumptions about the rate ofinitiation of isobutane pyrolysis. Combining these two independent experimentaldata gives the resultlog(a/cm3 mol-I s-l) = 14.2 - (141 kJ mol-'/2.303 RT)which is in very good agreement with the value determined in the present work.Indeed, at 800 K, the values of a calculated from the two expressions differ by only20 % which is certainly within any reasonable estimation of the possible error ineither expression.One further consequence of the presently suggested heat of formation of t-butylis worthy of note.The accepted thermochemistry of alkyl radicals based on groupadditivity leads to the conclusion that the bond dissociation energies (kJ mol-I) ofprimary, secondary and tertiary carbon-hydrogen bonds are almost in arithmeticprogression, viz. D(H--ethyl) = 410, D(H-isopropyl) = 394, D(H-t-butyl) = 381.Clearly, the suggested new value for the heat of formation of t-butyl destroys thissequence since it yields D(H-t-butyl) = 392.However it causes a new sequence ofbond dissociation energies (kJ mol-') to arise, viz. D(H3C-ethyl) = 354, D(H3C-isopropyl) = 350, D(H,C-t-butyl) = 348. Since no set of heats of formation couldlead to regular sequences of both C-H and C-C bond dissociation energies, it ispurely a subjective matter as to which, if either, of these sequences one would presumeto be reasonable. The presently suggested thermochemistry is not, therefore, to berejected on such grounds.10g(k6/kj/CM1" mol-+ S-') = 7.4-(74 kJ mol-'/2.303 RT)Note added in proof. The foregoing establishes, in our view, a need to identify the origin of the17 J mol-'l K-' overestimate of the entropy of t-butyl since we see no justification for the symmetrynumber proposal, a view shared, we now understand, by Golden who favours an explanation basedon a barrier to methyl group rotation in t-butyl.The authors thank the Foxboro Co., Foxboro, Mass.for the award of a studentshipto P. D. S .M. P. Halstead, R. S. Konar, D. A. kathard, R. M. Marshall and J. H. Purnell, Proc. ROJ~.SOC. A, 1969,310,52592 NEOPENTANE PYROLYSISF. Baronnet, M. Dzierzynski, G. M. Come, R. Martin and M. Niclause, Int. J. Chem. Kinetics,1971,3,197. ’ W. Tsang, J. Chem. Phys., 1966,44,4283.* W. Tsang, h t . J. Chem. Kinetics, 1973, 5, 651.P. D. Pacey, Canad. J. Chem., 1973,51,2415.R. S . Konar, J. H. Purnell and C. P. Quinn, Trans. Faraday SOC., 1968,64, 1319.A.P.I. 44 Tables, Selected Values of Properties of Hydrocarbons and Related Compounds (Thermo-dynamics Research Centre, Texas A. & M. University, 1971).H. E. O’Neal and S. W. Benson, Int. J. Chem. Kinetics, 1969, 1, 221.M. C. Lin and M. H. Back, Canad. J. Chem., 1966,44, 2357.l o H. Teranishi and S. W. Benson, J. Amer. Chern. SUC., 1963,85,2887,J. H. Knox and R. G. Musgrave, Trans. Furuduy Soc., 1967, 63,2201,l 2 K. Y. Choo, P. C, Beadle, L. W. Piszkiewicz and D. M. Golden, Abstracts, 168th Amer. Chem.SOC. National Meeting, Atlantic City, N.J., 1974.l 3 J. 0. Terry and J. H. Futrell, Cunad J. Chem., 1967, 45, 2327.l4 P. Camilleri, R. M. Marshall and J. €3. Purnell, J.C.S. Faraday Z, 1975, 71, 1491.l6 D. A. Parkes and C. P. Quinn, Clzem. Phys. Letters, 1975, 33, 483.l7 L. Batt, persona1 communication.I * D. M. Golden, 2. B. Alfassi and P. C. Beadle, Int. J. Chem. Kinetics, 1974, 6, 359.l9 D. Griller and K. V. Ingold, Int. J. Chem. Kinetics, 1974, 6, 453.2o R. Hiatt and S. W. Benson, Int. J. Chem. Kinetics, 1973, 5, 385.2 1 D. F. McMillen, D. M. Golden and S. W. Benson, J. Amer. Chern. SOC., 1972,94,4403.2a R. S. Konar, R. M. Marshall and J. H. Purnell, Znt. J. Chem. Kinetics, 1973, 5, 1007.J. A. Kerr and A. F. Trotman-Dickenson, Progr. Reaction Kinetics, 1961, 1, 105.(PAPER 5/712

ISSN:0300-9599    

DOI:10.1039/F19767200085

出版商:RSC    

年代:1976

数据来源: RSC