摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. TRANSACTIONS OF THE FARADAY SOCIETY Founded in I903 to promote the study of Sciences lying bet ween Chemistry Physics and Biology Volume 65 1969 Pages 1-1696 THE FARADAY SOCIETY LONDON @ The Faraday Society and Contributors 1969 P R I m D IN GREAT BRITAXN AT THE UNIVERSITY PRESS ABERDEEN

ISSN:0014-7672    

DOI:10.1039/TF96965FP001

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. TRANSACTIONS OF THE FARADAY SOCIETY Founded in 1903 to promote the study of Sciences lying between Chemistry Physics and Biology Volume 65 1969 Pages I 697-340 I THE FARADAY SOCIETY LONDON @ The Faraday Society and Contributors 1969 PRINTED IN GREAT BRITAIN AT THE UNIVERSITY PRESS ABERDEEN

ISSN:0014-7672    

DOI:10.1039/TF96965FP003

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Nuclear Magnetic Resonance of Aqueous Solutions of Alkylpolyoxyethylene Glycol Monoethers BY J.M. CORKILL J. F. GOODMAN AND J. WYER Procter & Gamble Limited Basic Research Dept . Whitley Road Newcastle upon Tyne Received 24th June 1968 Increasing the concentration of alkylpolyoxyethylene glycol monoethers in water results in an upfield shift of the water proton signal and a decrease in the longitudinal relaxation time. These effects have been discussed in terms of perturbation of the hydrogen-bonded solvent structure. Variable temperature experiments have revealed no discontinuities in the temperature coefficient of either the water chemical shift or the relaxation time in passing from the mesomorphic phase state to isotropic solution. The change in the chemical shift at phase boundaries has been shown to be associated with long-range order in the mesomorphic phases.It is concluded that in these systems the extent of motion and hydrogen bonding of the water molecules is independent of the nature of the phase and determined only by the temperature and composition of the system. Although other physical methods have been extensively applied to the investiga- tion of surface-active agents in water there have been relatively few studies using nuclear magnetic resonance (n.m.r.) techniques. The behaviour of the water resonance in dilute solutions of ionic surface-active agents has been investigated by Clifford and Pethica,lS2 and the effect of micellization on the solute signals in aromatic 39 and partially fluorinated materials has also been described. A study of the lyotropic mesophases given by surface-active agents with water and D,O has been made by Flautt and Lawson.6 The present study is concerned with the behaviour of the n.m.r.signals in aqueous systems of some non-ionic surface- active agents the n-alkylpolyoxyethylene glycol monoethers (C,E,) in both the isotropic micellar solution and mesomorphic phase states. EXPERIMENTAL MATERIALS The n-alkylpolyoxyethylene glycol monoethers C,E were prepared and purified by the methods previously described.' The terminally methylated compounds C,E,C were prepared by reaction of the appropriate monoether with thionyl chloride followed by condensation with sodium methoxide in methanol solution. These materials were purified by chromatography on silica gel using chloroform+ acetone mixtures as eluents followed by vacuum-distillation.SAMPLE PREPARATION Either doubly distilled water or I.C.I. 99.7 % D20 was used for sample preparation. Samples were made up by weight and mixed at a temperature at which an isotropic fluid was formed. They were either prepared directly in 5 mm ext. diam. Varian sample tubes or introduced by suction into 1 mm ext. diam. Pyrex capillary tubes. After sealing the capillaries were mounted concentrically inside Varian tubes by two Teflon bushes. 9 10 NUCLEAR MAGNETIC RESONANCE FOR C,E,+H20 For relaxation time measurements samples were made up on a vacuum line. After de-oxygenation by repeated freeze-thaw cycles the water was distilled into a Varian sample tube containing a known quantity of solute de-oxygenated in a similar fashion. The composition of these samples was checked by integration of the n.m.r.spectra. The criterion for effective de-oxygenation of the water was a relaxation time of greater than 4 sec at 30°C. N . M . R . MEASUREMENTS The n.m.r. measurements were obtained using a Varian DA60 system (external proton lock) operating at 60 Mc/sec. All chemical shifts are quoted in parts per million downfield of tetramethylsilane (TMS). As TMS altered the positions of the mesomorphic phase boundaries the resonance of the terminal methyl group of the alkyl chain was adopted as an internal reference. In those regions in which mesomorphic phases were not formed the separation between this signal and the TMS resonance was in common with other systems,8 independent of both temperature and composition. Chcmical shifts for capillary tube samples were determined relative to external TMS+CCl& (2 %) contained in the annulus between the capillary and Varian sample tube.The bulk susceptibility correction for this system was experimentally determined by measurements of the terminal chain methyl group resonances. It was 0-017p.p.m. at all temperatures of observation. Using the external field lock and pre-calibrated chart paper the accuracy (500 c/sec scale) is within f0.008 p.p.m. The spin-lattice (longitudinal) relaxation times TI were determined from the signal behaviour after saturation or adiabatic rapid passage to an accuracy of +lo0 msec. In all cases the signal changes were simple exponential functions of the time. The standard temperature control system was modified by the addition of an automatic heater power control which kept the gas stream around the sample at a constant chosen temperature.The relationship between the sample and gas stream temperature was deter- mined by inserting a calibrated thermistor into a spinning liquid sample. The system enabled temperatures to be selected and maintained to fO.1"C in the range 15-90°C. X-RAY MEASUREMENTS The capillary tube samples used in the n.m.r. measurements were examined by low-angle X-ray diffraction using the evacuated flat-plate camera described previo~sly.~ RESULTS CHEMICAL SHIFTS ISOTROPIC SOLUTIONS The spectra of CsE6 in D20 (33 % w/w 32°C) and C8E6 itself are shown in fig. 1 together with an assignment of the various signals. Those originating from the polyoxyethylene head group (EO) were assigned by comparison with the spectrum of C8E3 and triethylene glycol.The spectra of the other C,E compounds are similar. The C,E,C1 spectra have an additional signal -0.1 p.p.m. upfield of the EO signal group due to the methoxyl protons. In all these compounds in aqueous solution the alkyl chain shifts are independent of concentration whereas the water proton signal shows a shift variation over 1 p.p.m. and the EO signals show a smaller but significant (-0.13 p.p.m.) change. In fig. 2 the shift of the water proton signals for C8E3 CsE6 and C&&1 and in fig. 3 the EO group signals of CsE6 are shown as functions of the mole fraction of the solute species. The initial slopes of the water proton shift curves for a number of these compounds are given in table 1 . J . M . CORKILL J . F . GOODMAN AND J .WYER 1 1 4 3 2 I 0 chemical shift (p.p.m.) FIG. 1.-Spectra of (a) 33 % w/w C& in D20 and (6) pure CsE6 at 32C". 0 0.5 mole fraction solute 3 FIG. 2.-Chemical shift of the water protons in solutions of C8E6C1 El ; C8E6 0 ; CsE3 x at 32°C. The calculated relationship for CsE3 is shown by the broken curve. 12 NUCLEAR MAGNETIC RESONANCE FOR C,E,+H,O I . . 0 0.5 1.0 mole fraction CsE6 FIG. 3.-Chemical shifts of the ethoxide chain signals for CsE6 in water relative to the values in pure CsEB (C) El ; (D) 0 ; (E) x of fig. 1 at 32°C. TABLE 1 .-SLOPES (p.p.m./unit mole fraction) FOR INITIAL LINEAR PORTIONS OF CHEMICAL SHIFT-CONCENTRATION CURVES ( f0-08) alkyl chain length head group c6 c s Cto c12 1 -63 1-52 - E3 E3C1 I 1 *92 E6 2-07 2-02 1 -92 2-00 - 2-72 2.85 - E6Cl - - MESOMORPHIC PHASES In both the middle and neat mesophases given by the CI2E6 + H,O system* only one signal arising from the water protons is observed under high resolution condi- tions.In the 5 mm tubes the signals appeared to contain several overlapping components with a total width at half-height of 5-15 c/sec. depending in no obvious way upon the thermal and mechanical history of the sample. With capillary samples much more reproducible behaviour was observed with a clear correlation between the sample treatment and the n.m.r. spectra. The capillary samples were cooled slowly (0*5"C/h) from the isotropic region into the appropriate mesomorphic phase state at room temperature (20°C). The n.m.r. water signal and corresponding X-ray pattern for a neat phase sample are * For phase diagram see fig.1 Trans. Furaday Soc. 1969 65 287. J . M. CORKILL J . F. GOODMAN AND J . WYER 13 shown in fig. 4a. The annealed samples were then centrifuged back and forth in the capillary tube (5,000 g) and the n.m.r. and X-ray determinations repeated. The results of this treatment are shown in fig. 4b for the same sample. Qualitatively similar results were obtained from middle phase samples. In all cases the annealed samples gave oriented X-ray diffraction patterns and n.m.r. signals that were narrower and further downfield than those from the centrifuged samples which showed no preferred orientation. a b I 4.7 4.5 4.3 chemical shift (p.p.m.) FIG. 4.-Water signals and X-ray diffraction patterns (schematic inset) for CI2E6 +H20 neat phase (72 % w/w) at 32°C. (a) annealed sample (b) centrifuged sample.The position of the water signal is strongly temperature dependent moving upfield with increasing temperature irrespective of the phase and its treatment. At the mesophaselisotropic phase boundaries discontinuities in the shift against tempera- ture curves are observed large for the annealed samples small for the centrifuged samples. Typical results for neat and middle phases are shown in fig. 5. As the transition region is approached a second water signal appears and grows in intensity accompanied by the signals characteristic of the solute (fig. 6). The temperature range in which a double water signal is observed corresponds to the two phase co-existence region in the binary phase diagram. 14 WATER NUCLEAR MAGNETIC RESONANCE FOR C,E,,+H20 ETHY LE N E OXIDE I a' 3 temp ("C) FIG.5.-Temperature dependence of the water chemical shift in the C12E6+H20 system. 72 % w/w C12E6 neat El ; isotropic p~. 45 % w/w C1?E6 middle 0 0 ; isotropic a. The dependence for water is shown by the solid line. Transition temperatures are indicated by vertical broken lines. 4.5 4- 0 3.5 3-0 chemical shift (p.p.m.) FIG. 6.-Spectra of a 72 % w/w CI2E6+HZO sample in the neat to isotropic phase transition region. J . M. CORKILL J . F . GOODMAN AND J . WYER 15 RELAXATION TIMES The water signal intensities from capillary samples were too small to give accurate data and measurements of Tl were conducted on samples in 5 nim tubes. The results obtained were independent of the sample treatment although the line shapes were extremely variable. In fig.7 log TI is shown as a function of the reciprocal temperature (1/T) for neat and middle phase samples and for pure water. The transition temperatures for the mesomorphic phases are marked with dotted lines. There are no detectable discontinuities in the relaxation times on passing from the mesomorphic to the fluid isotropic states. t DISCUSSION ISOTROPIC SOLUTIONS In hydrogen-bonded systems the chemical shift of the protons involved is generally downfield with respect to the unassociated species.1o For water the difference in shift between the liquid and vapour states has been determined to be 4.66 p.p.m. at O°C.ll The introduction of solute molecules into water leads to two effects the disruption of water-water hydrogen bonds and the establishment of solute-solvent interaction. The effect on the chemical shift of the water protons is usually an upfield change relative to the pure liquid even with many ionic so1utes.12 Although the energy of interaction of the solute with the solvent may be greater than that of the solvent hydrogen bond the observed chemical shift change appears to be domi- nated by the extent of hydrogen-bond disruption.For a solute in which chemical exchange of protons can take place with the solvent the chemical shift will be further modified. If the exchange is rapid a single signal will be observed at a position determined by the solute and solvent shifts in the absence of exchange and the relative proportions of the sites available for exchange. 16 NUCLEAR MAGNETIC RESONANCE FOR C,Ey+H20 In the C,E,C1 systems where there is no solute-solvent proton exchange there is an approximately linear upfield shift of the water signal with increasing solute con- centration (fig.2). For @&& and C8E6C1 total water shifts are 2.9 p.p.m. and 2.7 p.p.m. respectively which are comparable with the value of 2.6 p.p.m. obtained by Satake et aZ.13 for water in dioxane. In both the C,E and C,EyC1 systems the methylene protons of the head group have chemical shifts that are dependent on composition (fig. 3) indicating that the electron distributions around the ether oxygens are perturbed by interaction with the water. The results for the C,E,C1 series are thus due to progressive replacement of water-water hydrogen bonds by water-ether oxygen interactions that involve a smaller change in chemical shift relative to un- associated solvent.The results for the C,E compounds may be analyzed on the basis of chemical exchange between the terminal OH-proton and water which has already undergone hydrogen bonding changes due to the presence of the solute. Chemical exchange leads to a single signal of chemical shift 8 given by where x is the solute mole fraction and 6 and 6 are the solute and water chemical shifts in the absence of exchange. The data for the C,EyC1 series suggest a linear change in the water chemical shift hence approximately 8 = [6,x + 26,( 1 - X)]/[2 - XI (1) 6 = a;-ax (2) where 6; refers to pure water and a is a constant. The effect of composition on 6 is difficult to assess but the results of Gillberg and Ekwall l4 for the decanol+water system suggest that in the absence of exchange the decanol QH-proton shift is nearly independent of composition hence 6 has been taken as a constant a; the value for pure solute.On combining these assumptions with (1) we obtain 8 = [26Z + (6; - 2(a + 6i))X 4- 2ax2-J/[2 - x]. (3) The gradient of this curve as x approaches zero is given by g = O*S(S,O - 6;) -a. (4) Both 6; and S,O can be accurately determined but a obtained from eqn. (4) is less exact as the initial gradient g is difficult to estimatc. Insertion of the appropriate values of 6; and 6 (fig. 2) and a obtained from 9 (table 1) into eqn. (3) for the C,E3 c water system leads to The agreement between the calculated relationship for 8 shown as a broken curve in fig. 2 and the observed relationship is reasonable in view of the simplified nature of the treatment the maximum discrepancy being 0-06p.p.m.at x = 0.5. Similar agreement has been obtained for the other systems studied although with the C,E conipounds the coincidence of the solvent and head group signals in the region of the maximum upfield shifts prevents a complete comparison. In this investigation the minimum concentrations were well in excess of the respective critical micelle concentrations hence all data refer to solute in the micellar state. For the same head group the chemical shift curves were superimposable and thus independent of the alkyl chain length as reflected by the data given in table 1. It has been suggested that the hydrophobic chain adjacent to the head group may still be in contact with the solvent in the micellar ~ t a t e . ~ Our results indicate that the amount of water involved is independent of chain length at least above C6.The increase in the magnitude of g in passing from the E3 to the E series reflects B = [9.48 - 7.78~ + 2.30x2]/[2 - XI. (5) J . M. CORKILL J . F . GOODMAN A N D J . WYER 17 the greater solvent perturbation due to the larger head group. The replacement of the hydroxyl by the methoxyl group (E to E,C1) also leads to an increase in g due more to the removal of the hydroxyl group with its associated downfield shift effect as for hydrogen peroxide l5 and alcohols than to any intrinsic disruptive effect of the methyl group. The decrease in longitudinal relaxation time TI with increasing solute concentra- tion at a given temperature may be attributed to the restriction of the solvent motion in the vicinity of the head groups (fig.7). The increase in the temperature coefficient of TI with increasing solute concentration implies that the micro-viscosity in the region of the head groups decreases more rapidly with temperature than in water itself. In contrast the temperature coefficient of chemical shift is only weakly dependent upon solute concentration (fig. 5) showing that the thermal disruption of water-water hydrogen bonds is scarcely affected by the presence of solute. MESOMORPHIC PHASES In the mesomorphic state the signals characteristic of the solute are too broad to be observed under high-resolution conditions. We may attribute this to a decrease in the extent of motion of the solute molecules relative to the isotropic solution on the formation of the mesophase.6 The solvent resonance however remains similar to that observed in the fluid isotropic state and therefore appears to retain a similar degree of mobility (fig.6). The double signal observed in the two-phase region indicates that chemical exchange between the co-existing phases is slow. Both line width and 8 for water in the mesomorphic phases depend upon the method of pre- paration of the sample and are clearly correlated with the ordering indicated by the X-ray diffraction data (fig. 4). The diffraction photographs of the slowly cooled mesomorphic phase samples exhibit equatorially disposed arcs. The structure of neat phase is lamellar,l 6* l7 consisting of bimolecular sheets of surface-active molecules separated by the solvent with the head groups oriented towards the solvent. The sharp diffraction spots arise from lamellae arranged parallel to the capillary walls.The effect of centrifugation is to produce a continuous diffraction ring with the same characteristic spacing corresponding to a random arrangement of the lamellae. In neat phase the long axes of the solute molecules are essentially normal to the lamellar plane hence in the ordered samples these will be oriented perpendicularly to the capillary axis. Thus in an orthogonal co-ordinate system if we take the static magnetic field to be directed in the 2-direction and the capillary axis to be the Y-direction then the solute long axes lie in the XZ plane. For annealed middle phase the axes of the cylindrical colloid units arranged in a two-dimensional hexagonal array,16* l7 show a preferential alignment parallel to the capillary axis.The EO head groups as in the ordered neat phase lie in the XZ plane. The effect of the anisotropy of one molecular species upon the chemical shift of another has been discussed in terms of the variation in the local magnetic field around the anisotropic species due to the anisotropy of its magnetic susceptibility.18* l9 In general a rod-like magnetically anisotropic molecule lying parallel to the magnetic field direction induces a downfield shift for the nuclei of a small molecule close to it. In the vicinity of the EO head group the water molecules are in an anisotropic environ- ment and hence the chemical shift will be dependent upon the relative directions of the magnetic field the axis of the EO group and the position vector of the water molecule with respect to the head group.In a macroscopic sample there will be exchange of the solvent protons between the various solute sites in particular between the EO head group region and the interlamellar fluid. The resonance position will thus be determined by the weighted mean of the various site shifts provided exchange 18 NUCLEAR MAGENETIC RESONANCE FOR C,E,+H,O is sufficiently rapid. In the oriented samples there will be a relative deficiency of EO groups arrayed in the Y-direction and hence the anisotropyeffect uponthechemical shift of the water close to the head groups will be different from that in a sample in which the EO groups take up all directions. The shift discontinuity in passing from the isotropic solution to the centrifuged mesophases varies in a random fashion between kO*Ol p.p.m. whereas the discontinuity for the ordered samples is much larger (-0.07 p.p.m.) and is consistently downfield (fig.5). The slight variability of the results for the centrifuged specimens is probably due to incomplete disorientation. We may conclude that in the absence of orientation effects the chemical shift- temperature relationship is a continuous function. The temperature coefficient of chemical shift is independent of the nature of the phase indicating that hydrogen bonding undergoes no radical change with phase transition. The longitudinal relaxation time T is also a continuous function of the temperature (fig. 7) showing the mobility of the water molecules to be independent of phase structure. J. Clifford and B. A. Pethica Trans. Furuday Soc. 1964,60 1483. J. Clifford and B. A.Pethica Trans. Furaday SOC. 1965,61 182. J. C. Eriksson Acta Chem. Scund. 1963,17 1478. H. Inoue and T. Nakagawa J. Physic. Chem. 1966,70 1108. N. Muller and R. H. Birkhahn J. Physic. Chem. 1967 71 957. K. D. Lawson and T. J. Flautt Mol. Crystals 1966 1,241. E. D. Becker U. Liddel and J. N. Shoolery J . Mol. Spectra 1958 2 1. J. S. Clunie J. M. Corkill J. F. Goodman Proc. Roy. SOC. A 1965,285 520. lo W. G. Schneider H. J. Bernstein and J. A. Pople J. Chem. Physics 1958 28 601 l1 J. C. Hindman J. Chem. Physics 1966,44,4582. l2 K. A. Hartman J. Physic. Chem. 1966,70,270. l 3 I. Satake M. Arita H. Kimizuka R. Matuura Bull. Chem. SOC. Japan 1966 39 597. l4 G. Gillberg and P. Ekwall Acta Chem. Scund. 1967,21 1630. l5 M. Anbar A. hewenstein S. Meiboom J. Amer. Chem. SOC. 1958 80 2630. l6 V. Luzzati and F. Husson J . Cell. Biol. 1962 12,207. l7 A. Skoulios Adv. Colloid Interface Sci. 1967 1 79. l9 A. D. Buckingham and E. E. Burnell J. Amer. Chem. SOC. 1967 89 3341. ' J. M. Corkill J. F. Goodman and R. H. Ottewill Trans. Faraday Soc. 1961,57 1627. A. D. Buckingham T. Schaefer and W. G. Schneider J . Chem. Physics 1960,32 1227.

ISSN:0014-7672    

DOI:10.1039/TF9696500009

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Additivity Relationships in Polar Diamagnetic Salts Part 3.-Double Salts of Magnesium and Zinc with Potassium and Ammonium and some Alums BY V. C. G. TREW S. F. A. HUSAIN AND A.J. SIDDIQI Department of Chemistry Bedford College Regent's Park London N.W. 1 Received 30th May 1968 Diamagnetic susceptibilities of a number of double salts of magnesium and zinc with potassium and ammonium have been measured in the solid state. Experimental values are close to the values calculated from the appropriate single salts assuming additivity but small systematic deviations have been observed. Magnetic susceptibility values are correlated with molar volumes of the salts and deviations interpreted in terms of changes in crystal lattice dimensions. A systematic study of the factors influencing the diamagnetic susceptibility of simple polar salts of alkali and some alkaline earth cations has been presented in parts 1 and 2.l". In this part the results of solid state measurements of dia- magnetic susceptibility and molar volumes for a number of double salts of magnesium and zinc with potassium and ammonium are reported.The influence of the co- ordination number of the ions in the lattice on these properties established for simple salts is further developed. Katti and Khanolkar have reported magnetic suscepti- bility values for a few double salts of magnesium and zinc including some of the present series and have interpreted small positive deviations from additivity in terms of weak electrostatic forces of an ion-dipole type. Experimental molar susceptibilities and molar volumes for the double halide salts and the Tutton salts of ammonium and potassium with magnesium and zinc and for the alums of the two univalent cations are shown in table 1.Results for thallium (I) alum and for aluminium sulphate are also included for comparison. Details of experimental measurements are as reported in the earlier papers. The experimental molar susceptibilities are shown in column 2 and (in brackets) the mean susceptibility of the anhydrous double salt assuming additivity for the susceptibility of the water in the hydrates. (- 106xHzo = 12.96 c.g.s. units). Litera- ture values are given in column 3. In column 4 the experimental molar volumes obtained from the densities of the salts are given. Calculated molar susceptibilities of the double salts derived from the single salt assuming additivity are shown in column 5 and in brackets the corresponding calculated values for the anhydrous double salts. Column 6 shows the increment in susceptibility per mole of water.This is obtained from the experimental molar susceptibilities in column 2 and the calculated anhydrous double salt susceptibilities of column 5. DISCUSSION The experimental molar susceptibilities of the double salts in almost all cases are reasonably close to the calculated value as deduced from the single salts but some small significant deviations occur. The ammonium halide series of double salts tend 19 20 ADDITIVITY RELATIONSHIPS I N DIAMAGNETIC SALTS - 106&f * expt. compound HALIDES NH4MgC13.6Hz0 (Z = 134) KMgC13 6H20 (Z= 142) NH4MgBr 6H20 (Z = 188) KMgBr 6H2 0 NH4Mg13 6H20 (2 = 196) ( Z = 242) (2 = 250) KMgI3 6HzO 166.78 f0.40 167.29 f0-11 (89.27) 165.99 f0-06 a 164.91 f0.09 (87-69) 196.94 f 1.3 197.33 k0.15 (1 19-37) 193-83 f0-78 (1 16.07) 246.95 rfi.1.1 250.90 f0-19 (171.14) 250-33 rt0-23 (1 72- 57) “ITON SALTS (NH4)2Mg(S04)26HZO 191.82 f 1.8 (Z= 208) K2Zn(S04)26H20 ALUMS NH4AI(SO4)212H20 (2 = 240) KAl(S04)212H20 (2 = 248) TlAl(S04)212HpO M2(so4)318H20 (Z= 310) (Z= 350) (1 14-06) 181.09 f0-28 181.20 k0.30 C (103.39) 192.89 f0-67 192.90 f0.26 C (1 15.13) 194.04 f0.31 194.58 f0-17 C (1 16.55) 253-63 f0.53 (98.1 1) 246.95 &O-8 1 (91.43) 266.16 f0.65 a (1 10.64) 335.61 fl-05 (1 02-3 3) TABLE 1 - 1 06XM lit. 168.74 - 198-7 - - - 192.21 1 9 1 ~ 4 ~ 202.1 1 9 8 ~ 8 ~ 2 1 0 ~ 4 ~ 24.3 252-3’ 251 *2S6 246.50’ 255.0’ 266.0’ 3 2 3 ~ 2 ~ Vg 175.9 172.0 196.1 192.6 226.6 218-3 212.10 187-65 208-0 197.6 275-6 270.0 275.7 377.1 - 106XMe calc. 164.18 (88.42) 166.33 (88.57) 196.04 (1 18-28) 198.91 (1 2 1 -1 5 ) 247-93 (1 70.1 7) 249.66 (171-90) 188.80 (1 1 1 -04) 189-18 (1 14-42) 191.86 (1 14.10) 192.24 (1 14-48) 240-08 (84.75) 240.27 (84-75) 262-98 (1 07.46) 352.40 (1 19-10) AXMH20f 13.43 12.8 1 13.14 12.1 1 13.12 13-07 13.46 11.62 13.13 13.3 1 14-01 13-52 13.23 12-03 * Experimental measurements a with magnetic field H = 4,750 oersted (Trew) ; by with H = 4,588 oersted (Husain) ; c with H = 4,544 oersted (Siddiqi) ; d this salt is difficult to prepare pure and to handle.The large hygroscopic crystals lose iodine readily. The value a was obtained by simple packing in the susceptibility tube ; the value b by sedimenting under benzene.9 e calculated by assuming XM (double salt) = XMX~+XM~X+~ZXH~O. f AXH~O represents the difference between the experimental susceptibility of the anhydrous salt and the calculated susceptibility of column 6 divided by the number of moles of water in the salt.It is the susceptibility difference per mole of water modified by the lattice differences as discussed in the text. V. C. G . TREW S. F. A HUSAIN AND A . J . SIDDIQI 21 to have mean susceptibility values a few units above the additive figure while those of the potassium salts are lower. The molar volumes in column 3 indicate that this would be expected. Ammonium double halides unlike the single salts have higher molar volumes than the corresponding potassium ones. This correlation of molar susceptibility and molar volume is similar to that noted in part 2 where the higher coordination number of ammonium chloride and bromide was shown to result in a lower molar volume and susceptibility.l P Hexahydrated ammonium magnesium chloride is isomorphous with hexahydrated potassium and rubidium magnesium bromides and with the mixed chloride-bromide double salt although carnallite itself has a different crystal structure. Since hexahydrated magnesium chloride and bro- mide are also isomorphous the enhanced susceptibility of the ammonium double salts appears to be due to the change in coordination of the ammonium ion in the double salt lattice. The sensitivity of the ammonium ion to changes in lattice struc- ture has been n0ted.l". In part 1 it was shown that a change in coordination number from 6 to 8 was responsible for a lowering of magnetic susceptibility of about 2-2 units of suscepti- bility of a similar magnitude to that shown in the present measurements. These deviations are reflected in the susceptibility increments for water in the last column of table 1.The increment for the ammonium salts is consistently slightly above the mean molar susceptibility of water (12-96) while that for potassium (except for the bromide) is close to the theoretical value. The molar susceptibilities of the four Tutton salts also show small deviations from additivity which can be interpreted from the lattice dimensions and consequent molar volumes. Lingafelter and Montgomery have determined the crystal structure and lattice dimensions of a number of double sulphates. The cell dimension para- meters for potassium double salts with magnesium show that the lattice of the double salt is considerably smaller than that of corresponding ammonium double salts. Substitution of zinc for magnesium in the lattice of double salts with ammonium also leads to smaller lattice dimensions.This evidently results in a smaller molar volume for potassium magnesium sulphate and for ammonium zinc sulphate relatively to ammonium magnesium sulphate. Although the lattice dimensions of potassium zinc sulphate have not yet been determined the molar volume is somewhat below that for ammonium zinc sulphate. The effect of these molar volume changes are responsible for the deviations from additivity of the molar susceptibility values shown in column 2. For these Tutton salts the normal molar susceptibility increment between the potas- sium and ammonium ions and between the zinc and magnesium ion as determined for the single salts la* is overlaid by the effect of changes in the lattice structure.The molar susceptibilities of the three alums studied and of aluminium sulphate octadecahydrate also show small deviations from additivity when compared with the single salt values. The effect is most marked for potassium alum where a lowered molar volume relative to the ammonium alum is again responsible for the lower molar susceptibility. have attributed the lowered susceptibility of aluminium sulphate sctadecahydrate to the effect of closer bonding of coordinated water by the small A13+ ion. The present results for this salt would support this since AxH2* = 12.03 in place of the free water measurement of 12-96. A rather higher molar susceptibility for this salt was obtained than that of these authors. The molar diamagnetic susceptibilities of these double salts are in general close to the additive value derived from the single salts but in addition the sensitivity of the property to changes in lattice dimensions is also well illustrated by those salts where the molar volume and molar susceptibilities show slight departures from additivity.Katti and Khanolkar 22 ADDITIVITY RELATIONSHIPS I N DIAMAGNETIC SALTS (a) V. C . G. Trew and S. F. A. Husain Trans. Furaday SOC. 1961,57,223. (6) V. C. G. Trew S. F. A. Husain and A. J. Siddiqui Trans. Faraday SOC. 1965 61 1086. K. V. Katti and D. D. Khanolkar J . Univ. Bombay 1960,27,32. R. W. G. Wyckoff Crystal Structures (Interscience 2nd ed. 1965) 3 801. H. Montgomery and E. C. Lingafelter Acta Cryst. 1964. 17 1478. C. H. Tinker Ph.D. Thesis (London 1937). M. Prasad S. S. Dharmatti C. R. Kanekar and N. S. Birader J. Chem. Physics 1949 17 81 3. 'I V. C. G. Trew Trans. Faraday SOC. 1936,32 1658. * G. T. Oddie Ph.D. Thesis (London 1937). V. C. G. Trew J . Chem. SOC. 1955 3911.

ISSN:0014-7672    

DOI:10.1039/TF9696500019

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Vibrational Emission by NO2 in Reaction of Nitric Oxide with Ozone. BY P. N. CLOUGH AND B. A. THRUSH Department of Physical Chemistry University of Cambridge Received 13th June 1968 Vibration-rotation emission associated with the transitions Avg = -1 Avl = Av = -1 and Av = -2 Av3 = - 1 of NO2 is observed from the reaction N0+03 = N02+02 a reaction which also yields electronically excited NOz.The vibrationally excited molecules are produced predomi- nantly by radiation and collisional quenching of electronically excited NOz followed by rapid re- distribution of vibrational energy rather than by direct population of high vibrational levels of the ground state. The reaction between nitric oxide and ozone NO + O3 = NO2 + O2 + 48 kcal/mole proceeds by two reaction paths with similar frequency factors but differing activation energies.lP The latter determine that at room temperature 93 % of the NO2 is formed in the 2A1 ground electronic state and 7 % in the 2B1 excited state.As an exothermic exchange the reaction might be expected to give rise to vibrational excitation in the product molecule containing the newly-formed bond and thus be an example of a reaction with parallel production of electronically excited and of vibrationally excited species. The vibrational emission reported here was first detected during studies of the electronic emission from the NO+03 reaction in the infra-red region but was not considered earlier because it exhibited several unusual features requiring further investigation. These investigations have led to the conclusion that the emitting vibrational levels of the ground state of NO2 are populated via the electronically excited state and not as expected by direct formation in the ground state. The results indicate that an electronically quenched molecule may still retain a substantial fraction of its initial energy as vibrational energy in the lower state a point on which there appears to be little previous direct evidence.Only two reactions have been previously reported to give simultaneous electronic and vibrational excitation the combinations H +NO and 0 + NO ; the vibrational emission observed in the latter system is similar to that found in the present work for NO + 03 and may have the same origin. EXPERIMENTAL Initial observations were made using the stainless steel reaction vessel described pre- viously.2 Subsequently two Pyrex spheres with an internal gold coating were employed of volumes 1 1. and 10 1. ; intensity gains of 20 or more are estimated to have resulted from the gold coating.The vessels were fitted with CaF2 or KBr windows and the smaller one was wrapped in electrical heating tape so that it could be heated to about 110°C. The fast pumping system has already been described; pressures were measured by McLeod or Pirani gauge. 23 24 VIBRATIONAL EMISSION BY NO2 Spectra were observed with a Grubb-Parsons GS2 infra-red monochromator frequently using only the CaF fore-prism section. The detectors were liquid-nitrogen-cooled PbS (Infrared Industries) or InSb (Mullard) cells or a Unicam Golay cell. Cylinder nitric oxide (Matheson) was purified by passage through a silica gel trap at -78"C followed by PzOs. Ozone was prepared as described el~ewhere.~ Other gases were taken from cylinders or prepared by standard methods and were well-dried before use.Flow-rates measured with calibrated capillary flow-meters. RESULTS VIBRATIONAL EMISSION BANDS Vibrational emission from the NO+O reaction was first detected in the region 3.4-3.8 ,u ; since this emission was relatively intense and lay within the range of the more sensitive PbS detector it was most fully investigated. Two traces of the spectrum at about 20 p Hg pressure with different ozone flow-rates (<NO flow rate) are shown in fig. 1. These were obtained using the 1 1. reaction vessel which yielded 3.9 3.8 3.7 3.6 3.5 3.4 FIG. 1.-Spectra of the 3.6 p emission at 20 pHg pressure. Origins and upper states of Av = Av3 = - 1 transitions are indicated. the greatest intensity for given flow conditions. With the PbS detector and 2 mm monochromator slit width high amplifier gains were needed and the spectra were consequently rather noisy ; nonetheless certain reproducible features could be identified.The sensitivity of PbS falls off with increasing wavelength in the region concerned but spectra obtained with the InSb detector which had a flat but lower sensitivity were little different. A second much weaker band was detected in the PbS range between 2.4 and 2 . 6 ~ ~ overlapping the electronic emission. This band could only be observed at prism resolution. No other bands could be detected in the PbS range and with the InSb cell which was sensitive up to 5 . 4 ~ ~ the only additional emission found was from the NO fundamental at 5.3 p. However with the Golay detector and fore-prism unit a P . N. CLOUGH AND B . A . THRUSH 25 region of relatively intense emission was found between 6 and 7.25 p with a peak a 6.2 p.For this region the optical path was sealed and flushed with dry air to reduce the strong atmospheric water vapour absorption. Extension of the investigations to wavelengths up to 20 p using a KBr prism failed to reveal any further emission. EFFECTS OF FLOW AND PRESSURE CONDITIONS The behaviour of the vibrational emission was examined under a wide range of flow and pressure conditions usually by comparing the peak intensity at 3.6 p with the electronic emission intensity at 1.5 p using the PbS detector For reaction in the 1 1. vessel with constant NO flow and approximately constant total pressure the rela- tive intensity of the 3-6 p emission rose with increasing addition of 03 as shown in table l(a). This suggested that a collisional process might be involved in populating TABLE 1 .-TEMPERATURE COEFFICIENT OF THE 3.6 p EMISSION BAND temp."C 0 3 flow total pressure !1+5 Il.SlI3.6 p moles/sec P Hg arbitrary arbitrary units (a> 20 0.8 17 1 1 1 -52 1-5 17 20-5 1.43 3.2 18 44 1-13 5.5 20 68 0.93 (b) 110 1.2 17 27 1 -50 1.8 17 46 1 -53 2.9 18 82 1 *47 the vibrationally emitting levels and further intensity comparisons were therefore made in which various nitrogen flows were added to fixed flows of NO and O3 (<NO flow). For each N2 flow the total pressure in the vessel was adjusted so as to main- tain the reagent concentrations at their initial values. Results obtained with the 1 1. vessel are given in table 2(u) and show that for an 11-fold pressure increase the electronic emission intensity falls by a factor of 6 whereas the vibrational emission TABLE 2.-QUENCETING OF THE ELECTRONIC AND VIBRATIONAL EMISSION BY Nz partial pressures I.C Hg 11.5 13.6 NO NZ arbitrary units arbitrary units (a) 17.0 0 40 35 17-0 35 18-5 38 17-0 83 11-5 38 17.0 1 70 6.5 38 17.0 330 3.5 29 (6) 6-0 0 13.0 23 6.0 9 7.5 23 6-0 26 4.5 23 6-0 51 - 22 intensity is practically invariant.The electronic quenching results yield a half- quenching pressure for N of 8 . 4 ~ Hg. With the lower initial pressure of NO of 6 p Hg the electronic emission again showed normal quenching behaviour with added Nz but the vibrational emission intensity doubled between 6 and 16p Hg with a slight further increase up to 3 0 p Hg. Table 2(b) shows that the latter effect dis- appeared when using the 10 1. vessel however and thus the intensity rise in the smaller vessel must have been due to reduced wall removal of the emitting species as added N2 increased the diffusion time to the wall.26 VIBRATIONAL EMISSION BY NO2 Measurements similar to those for N2 were also made with added C 0 2 and NO2. Addition of 15 p Hg of CO to an equal pressure of reagents left the 3.6 p intensity unaltered and addition of a further 3 0 p Hg produced only a 20 "/o intensity reduction. By contrast the 1.5 p intensity gave a good Stern-Volmer plot yielding a half-quenching pressure for CO of 3.8 p Hg. The results of table 3 show that NO had a different effect on the 3.6 p emission which fell off in intensity exactly in parallel with the electronic emission at 1.5 p. The latter had a half-quenching pressure of 4.1 p Hg agreeing within experimental error with the value obtained previously for the visible emission.2 TABLE 3 .-QUENCHING OF THE ELECTRONIC AND VIBRATIONAL EMISSION BY NO,.partial NO pressure I1.S arbitrary units !1-S/f3.6 arbitrary units 14.5 0 29-7 1.14 14.5 7.0 20-5 1-08 14-5 12.5 16.7 1-1 1 14.5 19-7 14-0 1.10 Spectra of the 3.6 p band obtained with excesses of the three quenching gases are shown in fig. 2. The changes in emission distribution are small considering the widely differing effects on the overall intensity observed. 3.9 3.8 3 *7 3.6 3-5 3'4 FIG. 2.-Spectra of the 3-6 I/. emission with added gases 16 WHg of reagents plus (a) 0.6 mm Hg of NP (b) 70 I/.Hg of COZ (c) 30 VHg of NOz. Further intensity comparisons were made between the 3-6 and 6 - 2 p emissions over a wide range of added N2 flows and pressures using the Golay detector and fore-prism unit.Between 17 p Hg and 0.5 mm Hg the intensity at 6-2 p rose relative to that at 3.6 p by about 15 % which is remarkably little for a 30-fold pressure in- crease. Similarly prism scans with the PbS detector showed that the ratio of intensities of the 2.5 and 3-6 p bands was effectively constant for pressures between 17 p Hg and 0.3 mm Hg. At the highest pressure the peak intensity in the 2-5 p band was appreciably greater than the peak electronic emission intensity a reversal of the situation at 17 p Hg. P. N. CLOUGH AND B . A . THRUSH 27 EFFECTS OF TEMPERATURE The temperature coefficient of the 3-6 p band was compared with that of the elec- tronic emission at 1-5 p to provide more evidence on the origin of the vibrational emission.The difference in activation energies of 1-85 kcal/mole should increase the rate of reaction into the excited state relative to that into the ground state by a factor of 2.1 on raising the temperature from 20 to 110°C. With the 1 1. reaction vessel heated to llO"C emission at 3.6 p from the vessel itself was much greater than that from the reaction and the compensation technique described by Orlova was therefore employed.6 Emission from the vessel passed through a rotating chopper disc set at 45" to the optical path on to a focussing mirror and thence to the monochromator. The aluminium chopper blades were blackened on the side towards the vessel and polished on the other side. Radiation from the compensating source an electrically heated copper block was reflected off the polished surface of the blades to the focussing mirror and monochromator which was thus exposed alternately to the reaction vessel and compensator.With the power supply to the compensator correctly adjusted radiation in the 3-6 p region from it exactly cancelled that from the vessel in the absence of reaction. Emission from the vessel and compensator at 1-5 p was undetectable. Intensity comparisons were made for reaction temperatures of 20 and 110°C using the PbS detector. The results are shown in table l(a) and (b). At 110°C the intensity ratio had the same value as the limiting ratio for low ozone flow rates at 20°C. Thus the temperature coefficients of the 3*6p and electronic emissions are the same. With the compensating system it was possible to obtain a spectrum of the 3.6 p band at 110°C.This did not differ significantly from spectra obtained under the same flow conditions at 20°C. DISCUSSION The emission in the region 6-7 p is due to the transition Av3 = - 1 of NOz for which the origin of the fundamental lies at 6-20 p . Since the intensity in this region parallels that at 3.6 p under widely varying conditions the same set of excited levels is probably concerned in both emissions so that the 3.6 p band can be interpreted as due to the superposition of many transitions with Avl = Av3 = -1. The (101)- (000) transition has its origin at 3*44p and the positions of this and several other origins calculated from the vibrational constants of Arakawa and Nielsen are indicated in fig. 1. There are intensity maxima slightly to the high frequency side of each of these origins where the intense R branches expected for type A transitions of NO2 should lie.For NO2 ~ 1 3 (28-7 cm-l) is almost twice as large as any other anharmonicity constant and the spacing of the maxima provides direct spectroscopic evidence of the nature of the transitions. Further support is provided by the vibra- tional emission in the 2-4-26 p region which is displaced from the 3.6 p band by vl and must be due to transitions with Avl = -2 Av3 = - 1 where (201)-4000) has its origin at 2-39 p. This interpretation of the 2-5 p band is consistent with the degree of vibrational excitation revealed in the 3.6 p emission. The distribution shifts for the 3 . 6 ~ emission induced by added C 0 2 and NO2 provide more evidence of the nature of the transition concerned.With C 0 2 v1 is in nearly exact resonance with the spacing of NOz energy levels of high v1 excitation so that these have a relatively greater relaxation rate than the lower levels and the emission intensity distribution is shifted to higher frequencies. The reverse is true 28 VIBRATIONAL EMISSION BY NO2 for NO2 and as shown in fig. 2 in its presence emission from the lower levels dis- appears completely. The temperature coefficient measurements on the 3.6 p band show conclusively that the ground-state vibrational levels emitting are populated via the excited electronic state which suggests that a mechanism such as the following may be involved NO + O,-+NO;+ O2 (14 NO;-+NO~ +hv (2) NOb+M+NOl+M (3) NO~,-+NO,+~V’ (4) NO; + M-+NO~ + M. ( 5 ) Here NO; represents an electronically excited molecule and NO; a ground-state vibrationally excited one which may emit quanta of v1 and v3.Processes (4) and ( 5 ) may involve more than one step. The large change in configuration between the two states of NOz means that radiation will invariably produce vibrationally excited ground state molecules; if it is assumed that a fraction a of quenching processes involve similar vertical transitions in NO2 steady-state analysis gives the vibrational emission intensity as With minor assumptions this relation can account for our observations. The temperature coefficient of the vibrational emission is effectively determined by kla giving a ratio of 3-6 p to electronic emission intensities independent of temperature Considering the behaviour with added gases it may be assumed initially that for pressures below 30 p Hg k 9 Xk5 [MI.In the region of the electronic half-quenching pressure-5-2 p Hg for NO 8-4 p Hg for N2-pressure independence of the 3-6 p intensity with added N2 was observed and this could only occur if a is close to unity i.e. both radiation and quenching from the excited state result in population of the emitting vibrational levels. Population by radiation alone would give parallel falls in electronic and vibrational intensities with increase in pressure whilst population by collision alone would lead to the vibrational intensity rising with pressure in this region. The different behaviour on adding NO2 is explained if a specific electronic quenching process yields ground-state molecules with little or no vibrational excita- tion.This is plausible in view of the electronic interaction between NO molecules leading to dimerization which is accompanied by the disappearance of the visible absorption spectrum. The intensity of electronic emission at 1.5 p is given by klak2[N0][O3]/(kz + Zk3 [MI). At low pressures the ratio of 3.6 ,u to 1-54 p emission is thus effectively (k2+ Xak3[M])/k2 and the increase in this ratio with ozone flow at 20°C (table l(a)) is due to efficient electronic quenching of NO2 by 03. The much smaller effect of increased ozone addition at 110°C results from the greater extent of reaction at this temperature which reduces the steady-state ozone concentration in the vessel. As long as k4 B Zk,[M] the intensity of vibrational emission should be independent of pressure of added gas.This was the case for added N pressure up to 0.2 mm Hg but for C02 the intensity began to fall at an added pressure of about 30 p Hg. The radiative lifetimes of the (101) and (001) vibrational levels of NO can be calculated from the corresponding absolute absorption intensities as 7.6 x sec respectively. The average radiative lifetime for the transitions involved in the and 643 x P . N. CLOUGH AND B . A . THRUSH 29 3.6 p emission would probably be a factor of 2 to 3 smaller than that of the (101) level if the findings for diatomic molecules that transition probabilities increase almost linearly with vibrational quantum number can be assumed to extend to triatomics. No measurements on the vibrational relaxation of NO appear to have been made but the molecule is sufficiently close to linear to be compared with other triatomics such as CO and N20.Spectrophone measurements have indicated that N2 is very inefficient in relaxing both v3 and v of C 0 2 and has low efficiency in relaxing v3 of N20. Resonant energy exchange effects between N2 and C 0 2 would be important but should be much less so for N,O. These results suggest long relaxa- tion times probably N sec at 1 atm for the v1 +v3 and v3 modes of NO2 in a large excess of N2 ; when combined with the radiative lifetimes this predicts vibra- tional half-quenching pressures (k4 = k5[N2]) of about 0.3 and 1.1 mm Hg respec- tively for the two modes. Thus the 3.6 p band intensity should fall off with added N2 at pressures around 0.3 mm Hg in satisfactory agreement with observation. The spectra of fig. 1 and 2 show that addition of 0.6 mm of N caused little intensity redistribution in the 3 6 p band and provide direct evidence of the low efficiency of nitrogen in vibrationally relaxing NO,.The slight increase in v3 emission relative to vl+v3 with added N is consistent with the above estimates. The results with added C 0 2 also agree with expectation. The vibration quenching efficiency of this gas should be much greater than that of N, leading to a fall of intensity at 3-6p with lower added pressures. The results indicate that COz is approximately 10 times as effective as N2 in relaxing the vl+v3 levels of NO2 and this greater efficiency is clear in the spectra of fig. 2. The effect of NO2 in reducing the 3.6 p intensity provides additional evidence that the emitting vibrational levels are populated from the excited electronic state.If NO2 only brought about vibrational quenching in the ground state the results could only be explained by assuming that the vibrational and electronic half-quenching pressures were identical-an unlikely coincidence. The total emission intensity in the 3.6 p vibration band (quanta sec-') is estimated as about 0.7 of the total electronic emission intensity for an NO pressure of 20 ~1 Hg when one in five of the electronically excited NO2 molecules formed emits. Thus the rate of v1 +v3 emission is about 0-15 times the formation rate of NO2 in the upper electronic state. Since the rate of emission of v3 quanta in the 6-7-25 p region is approximately 8 times that of v1 +v3 it is close to the formation rate of electronically excited NO, If radiation is the only process removing vibrationally excited molecules at low pressure as earlier considerations suggest a substantial fraction of the excited state molecules must retain vibrational energy after electronic quenching even allowing for the fact that one excited molecule may emit more than one quantum in succession.Moreover the presence of NO fundamental emission shows that part at least of the energy removed on quenching enters vibration of the collision partner. The ratio of intensities of the v3 and v1 +v3 emissions of NO is close to the ratio of the transition probabilities concerned and indicates that the same population of excited molecules is responsible for both emissions i.e. that excitation of v3 is normally accompanied by excitation of vl. The vibrational level 3v +v3 the highest which can be identified with certainty in the spectrum of the 3.4-3-8 p region has an energy of 15-5 kcal/mole above the ground level whilst the highest emitting level would have approximately twice this energy if the band were interpreted in terms of excitation of v1 and v3 only.Thus an appreci- able fraction of the total energy available in forming an electronically excited molecule (48 +4 = 52 kcal/mole) is appearing as vibration. We have interpreted the origin of the electronic chemiluminescence from NO + O3 in terms of a transition from low 30 VIBRATIONAL EMISSION BY NO2 vibronic levels of the linear or near-linear 2B1 state of NOz to the bent 2A1 state.2 If transitions on electronic quenching are " vertical " as for radiation then quenching like radiation should give ground-state molecules with considerable excitation of vz.It seems likely that the emission observed here results from rapid collisional redistribu- tion of this energy amongst the vibrational modes in the ground state and that the high probabilities for transitions with Av = - 1 and Av = Avl = - 1 as compared with other combination and overtone bands are responsible for only the former being detected. The extent of v excitation is impossible to estimate from the emission spectra in the 3-4-34 p region and no conclusions can be drawn from the absence of v2 +v3 and 2v +v3 which are very weak in absorption.'. lo The possible alternative to the above that excitation of v 1 and v3 accompanies the formation of molecules in the upper electronic state and is not lost on radiation or quenching to the ground state can be ruled out on energetic grounds since it would require the electronic origin to lie below 7,000 cm-l.Moreover the pressure inde- pendence of the emission shows that it is not a vibrational spectrum of the excited electronic state. Our results demonstrate that any contribution to the vibrational emission from NO2 formed directly in the ground electronic state is lower than that resulting from formation via the electronically excited state. This sets an upper limit of 7 % to the fraction of directly formed ground state molecules with v1 +v3 or v3 alone excited and since any vibrational excitation in such molecules should exist mainly as stretching of the new bond corresponding to the modes v1 and v3 rather than v2 we conclude that little direct vibrational excitation of ground state NO2 results from the reaction between nitric oxide and ozone.Stair and Kennedy have reported emission in the 3-7 and 6.3 ,u regions associated with the air afterglow in the combination of 0 with NO. They concluded that the 6.3 p emission was due to Av = - 1 transitions of NO from vibrational levels of the electronic ground state populated in part via the excited electronic state (a process analogous to that in NO+03) but suggested that the 3.7 ,u emission might be due to an electronic transition of NO,. In fact both bands must involve the same vibra- tional transitions of ground state NO as the emission in the corresponding regions found here. Our investigations of the air afterglow using 0 atoms generated by the titration of active nitrogen with nitric oxide failed to reveal any emission in the region 3-5-3.7 p for total pressures between 0.05 and 0.5 mm Hg though the electronic emission was observed up to about 2-1 p which is beyond the limit given by Fontijn et a2.l1 Stair and Kennealy used discharged molecular oxygen at pressures around 1 mm Hg where ozone is produced by the reaction and is removed by and by reaction (1).At 300"K kl -2k7 1 s l 2 and since k6~k8/100,12 O+Oz+M = 0 3 + M (6) 0+03 = 202 (7) O+NO+M = NO,+M (8) the rates of production of NO2 by (6) followed by (1) and by (8) will be comparable when [O] and [NO] are ca. 1 % of the oxygen carrier. At room temperature 7 % of reaction (1) yields electronically excited and then vibrationally excited NO2. In reaction (8) the fractional yield of electronically excited molecules is probably higher,' but it is feasible that the vibrational emission and some of the low frequency electronic emission observed by Stair and Kennealy originated from reaction (1) rather than (8).P . N. CLOUGH AND B . A . THRUSH 31 M. A. A. Clyne B. A. Thrush and R. P. Wayne Trans. Faraday Soc. 1964 60 359. P. N. Clough and B. A. Thrush Trans. Faraday Soc. 1967 63,915. J. K. Cashion and J. C. Polanyi J. Chem. Physics 1959 30 317. A. T. Stair and J. P. Kennealy J. Chim. Physique 1967,64 124. P. N. Clough and B. A. Thrush Chem. and Ind. 1966 1971. I. N. Orlova Optics Spectr. 1965 19 381. A. Guttman J. Quant. Spec. Rad. Trans. 1962 2 1. T. L. Cottrell I. M. Macfarlane and A. W. Read Trans. Faraday SOC. 1967,63,2093. ’ E. T. Arakawa and A. H. Nielsen J. Mul. Spectr. 1958,2,413. lo G. E. Moore J. Opt. SOC. Amer. 1953,43 1045. l1 A. Fontijn C. B. Meyer and H. I. Schiff J. Chern. Physics 1964 40 64. l2 M. A. A. Clyne D. J. McKenney and B. A. Thrush Trans. Faraday Suc. 1965 61,2701. l 3 M. A. A. Clyne and B A. Thrush Proc. Roy. SOC. A 1962,269,404.

ISSN:0014-7672    

DOI:10.1039/TF9696500023

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Some New Vacuum Ultra-violet Emissions of Active Nitrogen BY I. M. CAMPBELL AND B. A. THRUSH Dept. of Physical Chemistry Lensfield Road Cambridge. Received 1st July 1968 Vacuum ultra-violet emission by the a‘lX; state of Nz and by N((3P)3s(2P)) have been detected in active nitrogen together with the previously reported Lyman-Birge-Hopfield bands.The a‘ state is populated and removed by atomic nitrogen in the reaction and quenching by Nz but not radiation is also significant in removing the a‘ state. N(4S3 +Nz(B311g) +Nz(a’l&) + N(4S:) The only reported ultra-violet emission associated with the Lewis-Rayleigh nitrogen afterglow is the Lyman-Birge-Hopfield System resulting from the transition N2(a111g)+NZ(X1C’B+) which is allowed as magnetic dipole but not electric dipole radiation. Tanaka Jursa and LeBlanc detected bands emanating from N,(a’ll,)v’ = 0 1 and 2 spectroscopically while Young,2 using an iodine Geiger counter detected emission from N2(a11Tg)~’ = 4 5 and 6.The forbidden transition N2(a’lC,)v’ = O+N,(XIC,+) gives rise to bands in the vacuum ultra-violet region which have been observed spectroscopically in emission from a transformer discharge in nitrogen greatly diluted with argon.3 This transition has also been observed in absorption in a path of 3.4 m atm of pure nitrogen ; this study gave a radiative lifetime of 4 x sec for N,(a’lC’;) by comparison with the absorption intensity of the Lyman-Birge-Hopfield transition a radiative lifetime for N,(allIg) of 1.7 x sec having been determined in a molecular beam e~periment.~ We report the detection of NZ(d1E;)u’ = O+N,(XIZ:) emission in the nitrogen afterglow ; the observed bands are interspersed between stronger Lyman-Birge-Hopfield bands. Emissions due to atomic nitrogen transitions from N(2~~2p~(~P)3s(~P)) to N(2Po) and N(2D”) have also been detected; these have not been noted previously in the Lewis-Rayleigh afterglow.EXPERIMENTAL Nitrogen (B.O.C. White Spot) puraed as described previouslyy6 together with a trace of oxygen (<0.05 %) to promote dissociation was flowed through a microwave discharge (Microtron 2450 Mc/sec) in a quartz tube (14 mm ext. diam.). The resultant active nitrogen passed into the observation vessel shown in fig. 1 some 0-1 sec downstream of the discharge. Under our conditions any formation of the “ pink afterglow ” occurred well before the Wood‘s horn light traps (B) and no evidence (e.g. N2 second positive emission) was found to suggest that the observation vessel contained other than a Lewis-Rayleigh afterglow. Argon (B.O.C.) was purified as described previously and could be added to the nitrogen before the discharge.The observation vessel was viewed axially from the upsteam end through the Pyrex window by the R.C.A. 1 P 28 photomultiplier ID with a Wratten 22 filter P to isolate NZ first positive emission in the region 5600-6000 8 ; the collimation hole C ensured that light reflected from the walls of the vessel was not detected. The downstream end of the vessel was fitted to a McPherson model 218 0.3 m (f/5-3) scanning vacuum monochromator. The parts of the endplate holding the LiF window H were cemented together and to the 32 I . M. CAMPBELL AND B . A. THRUSH 33 observation vessel with an epoxy-resin. The design of the vessel with 4 exit ports K close to the LiF window eliminated " dead space ',.Radiation passed through the monochromator and was detected with an E.M.I. 6256 B photomultiplier placed behind a sodium salicylate window ; the salicylate was deposited using the method of Knapp,8 to a thickness of - 2 mg/ cm2. Monochromator entrance and exit slits of 6Wp width were needed to give good signal/noise ratios. The grating and mirrors were coated with MgF2 and the grating had 2400 grooves/mm blazed for 1500 A. The voltage generated across a photocell load resistance of 47,000 ohms was measured on a 1 mV potentiometric recorder. For the weakest signals a 50pF condenser (giving a time constant of 2-5 sec) ensured that the noise was always less than 20 % of the measured signal. For stronger signals a 0-4sec time constant circuit was used. Dark current and 0 1 M IN L FIG.1 .-The observation system (not to scale). A flow of active nitrogen from discharge ; B Wood's horns ; C photomultiplier collimator (7 cm long x 2 mm diam.) ; D R.C.A. 1P28 photomultiplier ; E observation vessel (15 cm longx 36 mm int. diam.); F outer jacket (52 mm int. diam.) ; G aluminium holder with glass facing; H LiF window (22 mm diam. 4 mm thick) ; J titration iet ; K four exit ports to outer jacket ; L holder attaching vessel to monochromator ; M monochromator entrance slit ; N to valve and pumping system; 0 Neoprene O-ring ; P Wratten 22 filter. the photocurrent associated with stray light were constant across the range 1000-1900A and were eliminated by a " backing off " circuit which was adjusted with the monochromator set at 1000 A where no direct radiation can be detected.Intensity measurements were made by recording the signals received over a period of time with the monchromator set on the centre of a band and on the background signal. This proved an accurate method of averaging noise and eliminating the possibility of drift. There was no evidence of or reason to expect any change in rotational distribution within a vibrational band which could affect the accuracy of relative measurements made in this way. Both photomultiplier cells were fed from stabilized high voltage supplies which were maintained at a fixed setting throughout a series of measurements on any one band. The 1P28 cell monitored the N2 first positive emission from the observation vessel ; the intensity of this emission is strictly proportional to [NI" and an absolute calibration was made by titrating the nitrogen atoms with nitric oxide at the jet J in the entry to the observation vessel.Decay of atoms along the length of the vessel was negligible under ow conditions. 2 34 ULTRA-VIOLET EMISSIONS OF ACTIVE NITROGEN With mixed carriers allowance was made for the enhancement of the first positive emission on partial replacement of nitrogen by argon as observed previously.6 The total pressure [MI in the reaction vessel was measured using a silicone oil manometer. Our kinetic measurements were made near 1700 A. The concentrations of O2 present were such that in this region the Schumann-Runge system could not cause any significant absorption according to published data.g The nitrogen atom concentration was varied both by altering the amount of oxygen added and by altering the discharge power.RESULTS Fig. 2 is a typical scan of the vacuum ultra-violet emission from active nitrogen. It shows relatively strong Lyman-Birge-Hopfield (L-B-H) bands arising from levels v' = 0 1 and 2 of N2(a111g). An additional band was detected near 1710 A which decreased in intensity less slowly with increasing pressures in the range 2-7 mm Hg than the L-B-H bands and was more enhanced by dilution of the nitrogen carrier with argon. Although the structure of this band is not resolved by the slow scan given in fig. 3 on kinetic grounds it is clearly not an L-B-H band. The nearest one is the (2,6) with its head at 1703 &lo an estimate of the intensity of this band from that of other L-B-H bands with v' = 2 using calculated Franck-Condon factors l1 shows that it could make little contribution to the emission observed in this region.Its greater width and lack of a pronounced head support its assignment to the (0,4) band of the N,(a'lZ;-,XIC,+) (hereafter denoted Nz(u'+X) system) which has its origin at 1707A. The bands of this system contain only Q branches degraded towards longer wavelengths but at low dispersion they appear broader and more symmetrical than the L-B-H bands which have a well-defined head to shorter wave- lengths.lo From its similar appearance and kinetic behaviour a band just below 1650 A can be identified as the (0,3) N,(a'-,X) band with origin and not as the (6,8) L-B-H band with head at 1648 A. In this way features around 1538 1587 1774 and 1846A could be attributed to the (O,l) (0,2) (0,5) and (0,6) bands of the N,(a'-,X) system ; the first two have not been reported previously.No emission from higher vibrational levels of the N2(a'lX;) state could be detected. Measure- ments were made using the well-separated (0,4) band. The intensity Iw of this band was between second and third order in [N] and decreased with increasing pressure in the range 2-5-5-0 mm Hg. A plot of [Nl2/Iw against [N,]/[N] was linear as shown in fig. 4. A least squares analysis gave at 1644 for N2 carriers where the ratio [N,]/[N] was varied by a factor of 3. The error limit quoted is twice the standard deviation The (a'-+X) emission therefore obeys a relation of the form I w = B"l3/("1 + C",I). (ii) This emission like the Nz first positive emission is enhanced by replacement of the N2 carrier by argon.The lower two lines in fig. 4 are drawn assuming that replace- ment of 48 or 72 % of the nitrogen carrier increases B in eqn. (ii) by the same factors 1-53 and 2.13 found for the enhancement of the first positive emission. Unfortunately the accessible range of [Nz]/[Nl is too small to define the slopes of these lines accurately but the agreement between the calculated lines and points is striking. The (a'lz;) state does not correlate with ground-state nitrogen atoms (fig. 5 ) ; its kinetic behaviour given by eqn. (ii) suggests that it is removed by nitrogen atoms and Nz molecules but not by argon. It must be populated by interaction between 1. M . CAMPBELL AND B. A. THRUSH 35 a nitrogen atom and an excited nitrogen molecule the steady-state population of which in the Lewis-Rayleigh afterglow is proportional to [N12 and independent of total pressure i.e.a state which is populated by three-body recombination of N atoms and removed predominantly by quenching by the carrier gas. I I 1800 1700 1600 ii 15100 Id00 1300 A FIG. 2.-Low sensitivity scan across the vacuum ultra-violet emission produced by active nitrogen containing 75 % argon at -5 mm H g total pressure with 400 p slits showing Lyman-Birge-Hopfield (N2(a111g -+XIZi)) and Nz(a"E; +XICi) bands. I I 1720 1710 1700 1691 FIG. 3.-High sensitivity slow (2 A/min) scan across the (0,4) Nz(a' + X ) band emission in pure nitrogen at a total pressure of -3 nim Hg with 2.5 sec time constant detector and 600 p slits. 36 ULTRA-VIOLET EMISSIONS OF ACTIVE NITROGEN 0 “ Z l l M x FIG. 4.-Plots of [N12/Iw against [N,]/[N] in pure nitrogen (I) nitrogen containing 48 % argon (11) and nitrogen containing 72 % argon (111).FIG. 5.-The potential curves of molecular nitrogen (according to Giln~ore.~~) I . M. CAMPBELL AND B. A. THRUSH 37 The similar behaviour of the coefficient B in eqn. (ii) and the first positive emission on dilution with argon suggests that N2(B311,) is the precursor of N2(d1Z;) rather than high vibrational levels of the N,(A3ZC,+) state which are populated in a large proportion of nitrogen atom recombinations. This unexpected result is explained by the electronic correlation rules l 3 involved in the transition state of the reaction N(4Su) + Nz = NJC,) + N(4Su) where a plane of symmetry is preserved throughout. Energetics require that the nitrogen atom stays in its ground electronic state; the transition state must have A’ symmetry (sign unchanged on reflection in plane of N atoms) and can correlate with N(4Su) + N,(B311g) but not with N(4Su) + N2(A3Z;).ABSOLUTE INTENSITY The absolute intensity of the (a‘+X) emission was found by comparing the integrated area of the (0,4) band with that of the (0,O) 6 band of nitric oxide at 19108 produced by the trace of oxygen atoms present as impurity ([O]-[NI/30); the (0,2) L-B-H band at 1554A was used as an intermediary standard because of the great difference in intensities. For these experiments a calibrated constant impedance attenuator was interposed between the photomultiplier and the recorder. The absolute intensity of the NO 6 bands is l4 I(S)/“J[O] = 6.6 x loG cm3 mole-1 sec-’ and the appropriate values of [r\J1 and [O] were found by partial titration of nitrogen atoms with nitric oxide? From the Franck-Condon factors for the NO 6 bands given by Nicholls,15 the (0,O) band was taken to be 0.18 of the total 6 band intensity.The intensities of the N2(a’+X) bands given by Ogawa and Tanaka,3 together with our estimates for the (0,2) and (0,l) bands which are relatively weak allowed an estimate that the (0,4) band represented 0.22 of the total Nz(a’-+X) intensity. Hence a value of r = 3.2 x 1031~]2/(1+ 5.5 x i0-3m21/[~) in cm3 mole-l sec-l was obtained. This is probably accurate to within a factor of 2. Reasonable assumptions were made that the fluorescence efficiency of the sodium salicylate and the efficiency of the grating (which is blazed at 1500A) did not change significantly between 1700 and 1900 A.LYMAN-BIRGE-HOPFIELD BANDS Young has shown that the intensity of the L-B-H emission from N2(a1TI[,)v’ = 6 5 4 at around 1300A is proportional to [w2/[M] after taking into account the pressure independence of N2 first positive emission. Such emission appears weakly in figure 2. We have examined L-B-H emission from levels v’ = 2 1 and 0 whose relative populations under our conditions are roughly in the ratios 1 2.5 6. We find complex emission kinetics resembling those of the (a‘-+X) emission with a rate of population which is higher than second order in [Nl and enhanced by argon carriers. The main removal processes appear to be quenching and vibrational relaxation by the carrier gas ; removal by N atoms and radiation are also significant the competition in the mm Hg pressure range being produced by the shorter radiative life of the alQ state (1-7 x sec).sec) as compared with the a’lZ; state (4 x 38 ULTRA-VIOLET EMISSIONS OF ACTIVE NITROGEN EMISSION BY NITROGEN ATOMS At pressures above 5 mm Hg with the higher nitrogen atom concentrations the intensities of the N atomic lines at 1493 and 1744A became comparable with the stronger LB-H bands; the lines are unresolved doublets and are transitions from N(2~~2p~(~P)3s(~P)) to N(2Do) and N(2Po) respectively. No other emission by atom nitrogen was observed. The transition 4P+4S0 at l200A could not be detected although the upper state has the same electronic configuration as the emitting 2P state and lies some 0-34 eV below it. The failure to detect this transition probably arises from re-absorption of the radiation by ground-state nitrogen atoms and low transmission by the LiF window than from lack of population of the 4P state.The emitting ((3P)3s(2P)) state of N has an excitation energy of 10.67 eV which is 0.91 eV more than the energy available from the recombination of ground-state nitrogen atoms. The intensity of its emission lines is apparently third order or more in (N) and in [MI although the precise dependence could not be found with the present apparatus. This suggests that the excitation involves the energy froin more than one nitrogen atom recombination. The only excited states of N lying below the ((3P)3s(2P "P)) states are the metastable 2Do and 2Po states at 2.38 and 3.58 eV; these are the intermediates for multistep excitation. It is known from mass spectro- metry and vacuum ultra-violet absorption spectroscopy * that these species only persist for about 1 msec downstream from a discharge at total pressures around 1 mm Hg ; this is believed to be due to their efficient removal on surfaces.Noxon l9 observed emission by N(2Po) from active nitrogen at high pressures. His data can be recalculated to allow for the absence of pressure dependence of the nitrogen first positive emission intensity which he assumed to exist. The intensity of N(2Po) emission for pressures between 20 and 760 mm Hg is then consistent with a mechanism in which N(2Po) is formed by reaction (2) and removed by reaction (3) and at the walls N(2P0)+N(4S0) = N(4So)+N(4So) or (2Do). (3) Using the calculated radiative life 2o of 12 sec for N(2Po) the concentration of N(2Po) in Noxon's experiments appears consistently slightly less than that of N2(A3E.,+) as it would be if k and k3 were comparable.At the lower pressures used in our work wall removal of N2(A3Z,+) and N(2Po) will predominate; the [MJ-l dependence of the diffusion rate will result in a higher power dependence 21- 22 of [N(2Po)] on both FT] and [MI. The excitation of N(2Po) to N((3P)3s(2P)) by the energy released in a further recombination of nitrogen atoms would then give the required strong dependence of the intensity of the atomic emission on CN] and [MI. The A3X=,+ state of N2 which is frequently invoked in excitation mechanisms 21s 22 does not have enough energy to excite N(2Po) to the ((3P)3s(2P)) state unless it has at least six quanta of vibrational energy.It is likely that the concentration of N(2Do) is higher than N(2Po) ; however this state requires greater excitation to reach the emitting 2P state. DISCUSSION The conversion of the absolute intensity of the (a'+X) emission in active nitrogen to an absolute concentration of N2(af1Z;) requires a knowledge of the radiative life of this transition. Mulliken and Wilkinson gave 4 x sec based on the life- time of N2(a1n,) of 1.7 x sec determined by Lichten in a molecular beam experi- I . M. CAMPBELL AND B . A . THRUSH 39 ment in which this state was not positively identified. Accepting this value the steady-state concentration of N2(a' 'Xi) in active nitrogen is approximately For the N2(B311g) state the corresponding figure is 5O[Nl2 taking the radiative life23 for the first positive bands to be 6 x The populations of the a'lZ; and B3ng states are thus comparable which would support the mechanism suggested below 13O[Nl2/(1 +5*5 x 10-3[N2]/m) mole ~ m - ~ .sec. N2(B311g) + N(4Su) +Nz(u'lZ;) + N(4S,,) N2(a"E;) + N2(X1Z:) = quenched products ( 4 7 -4) ( 5 ) (6) N2(u"ZU-) = N2(X1Zl) + hv yielding for k6 -4 k- 4[N] + k,[N2] which has the correct kinetic form and dependence on carrier composition. Although three other excited states of N2 (fig. 5 24) lying below the first dissociation limit could undergo reaction (4) with conservation of parity the wlAu state is not known to be populated in active nitrogen and the alng state shows the wrong pressure dependence. The pressure dependence of the population of the E 3 C ; state is not known and the effect of argon carriers is almost certainly different from that on the B3n It is however the only state other than B317 to which reaction (-4) can occur.The lowest levels of the B' state which such a reaction could populate are not observed in active nitrogen although the B'-B transition is strong.26 We therefore consider that the N2(B311,) state is involved predominantly in reac- tions (4) and (-4). The above mechanism is however a simplification as it does not consider the wide vibrational energy distribution of N2(B311g) in active nitrogen reaction (4) being exothermic for v' 2 6 and endothermic for 0' < 5. As only about one quarter of the B31-Ig molecules have 11'36 in a nitrogen carrier,26 k4 must be greater than k-4 if the above radiative lives are accepted. If (4 -4) is an exchange reaction it is hard to understand why k4> k-4 since vibrational energy has only a low probability of being able to overcome a potential energy barrier.A collision-induced radiationless transition between excited electronic states of N2 is more consistent with k4>km4 since the potential curves of the a' and B states are closer at high energies where (4) occurs than at the lower energies appropriate to (-4) (fig. 5). The value of k6 and hence of the ratio k4/k-4 could be in error. Mulliken and Wilkinson's work gives a radiative life of 2.6 x sec for the A31=,+ state of N2 which is some 50 times less than the currently favoured value.27* 28 A corresponding decrease in k6 would however increase the ratio k4/k-4 and yield an implausibly high concentration of the a"Z; state. We there- fore consider that k6 -25 sec-' ; accepting this kq k-,> 10 cm3 mole-' sec-' and k5 > 5 x los cm3 mole-1 sec-1 would give the observed kinetics.Under all experimental conditions the population of the B311 state (and the intensity of the first positive emission) was accurately proportional to [N2. This state is removed predominantly by collisional quenching by N for which the rate constant ti is close to lo1 cm3 mole-' sec-1 ; since [N2]/[Nl 3 100 under our conditions the condition that reaction (4) does not affect the kinetics of the first positive emission significantly is k4< lOI4 cm3 mole-' sec-l an upper limit which is close to the collision number. 40 ULTRA-VIOLET EMISSIONS OF ACTIVE NITROGEN We thank the Royal Society for the loan of a vacuum monochromator. Note added in Proof.-Tilford Wilkinson and Vanderslice 29 have re-assessed the relative intensity measurements on the a c X and a’+- X systems of N2.Ching Cook and Becker 30 have measured the absolute intensity of the a +- X absorption ; this yields a radiative life of 2.5 x sec for the alIIIg state which is to be preferred to Lichten’s value of 1-7 x sec from a beam experi- ment in which the all& state was not positively identified. These new data yield a radiative life of 0.1 sec for the a’ state (k6 = 10 sec-l) ; this increases the estimated concentration of the a’ state by a factor of 2-5 but does not invalidate any of the arguments presented here. Y. Tanaka A. Jursa and F. LeBIanc The Threshold of Space ed. M. Zelikoff (Pergamon Press New York 1957) p. 89. R. A. Young J. Chem.Physics 1960,33 11 12. M. Ogawa and Y. Tanaka J. Chem. Physics 1960,32,754. P. G. Wilkinson and R. S . Mulliken J. Chern. Physics 1959 31,674. W. Lichten J. Chem. Physics 1957 26 306. I. M. Campbell and B. A. Thrush Proc. Roy. SOC. A 1967,296,201. G. F. Beale and H. P. Broida J. Chem. Physics 1959 31 1030. R. A. Knapp Appl. Opt. 1963,2,1334. K. Watanabe E. C . Y. Inn and M. Zelikoff J . Chem. Physics 1953 21 1026. R. N. Zare E. 0. Larsson and R. A. Berg J. Mol. Spectr. 1965 15 117. lo R. T. Birge and J. J. Hopfield Astrophys. J. 1928 68 257. l2 I. M. Campbell and B. A. Thrush Trans. Faraday Soc. 1968 64 1275. l 3 K. E. Shuler J. Chem. Physics 1953,21 624. l4 R. A. Young and R. L. Sharpless J. Chem. Physics 1963,39 1071. l6 R. Allison J. Burns and A. J. Tuzzolino J. Opt. SOC. Amer.1964,54 747 1381. l7 S. N. Foner and R. L. Hudson J. Chem. Physics 1962,37 1662. l8 F. A. Morse and F. Kaufman J. Chem. Physics 1965,42 1785. l9 J. F. Noxon J. Chem. Physics 1962 36 926. *’ R. H. Garstang The Airglow and Aurorae ed. E. B. Armstrong and A. Dalgarno (Pergamon 21 W. R. Brennen and G. B. Kistiakowsky J . Chem. Physics 1966,44,2695. 22 J. C. Boden and B. A. Thrush Proc. Roy. Soc. A 1968,305,93. 23 M. Jeunehomme J. Chem. Physics 1966,45,1805. 24 F. R. Gilmore J. Quant. Spec. Rad. Transfer 1965 5 369. 25 F 3. LeBlanc Y. Tanaka and A. S . Jursa J. Chem. Physics 1958 28,979. 26 K. D. Bayes and G. B. Kistiakowsky J. Chem. Physics 1960,32,992. 27 W. Brennen J . Chem. Physics 1966,44,1793. 28 T. Wentink and L. Isaacson J. Chem. Physics 1967 46 822. 29 S. G. Tilford P. G. Wikinson and J. T. Vanderslice Astrophys. J. 1965,141,347. 30 B. K. Ching G. R. Cook and R. A. Becker J. Quant. Spectr. Rad. Transfer 1967,7 323. R. W. Nicholls J. Res. Nut. Bur. Stand. A 1964,68,535. Press London 1956) 324.

ISSN:0014-7672    

DOI:10.1039/TF9696500032

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Spectra and Hydrogen-Bonding of Characteristics of Thiocyanic Acid Part 4.- Association with Weak Proton Acceptors. BY T. M. BARAKAT * JANE NELSON S. M. NELSON AND A. D. E. PULLIN 7 Dept. of Chemistry Queen's University Belfast. Received 3rd May 1968 Free energy enthalpy and entropy changes for the 1 1 association of iso-thiocyanic acid with a series of organic sulphides selenides nitriles thiocyanates aromatic hydrocarbons and with nitromethane in carbon tetrachloride soIution at 25°C are reported. The thermodynamic data are compared with those for other proton donor complexes and are discussed in terms of electro- negativity of the proton acceptor atom ring strain steric and inductive effects and the frequency shifts of the fundamental vibrations of HNCS on bonding.Departures from the Badger-Bauer rule for complexes with the more polar bases are attributed to an electrostatic interaction between the base and the NCS moiety of the acid. A rough corres- pondence between the enthalpy and entropy of association for all the bases studied is found and the factors influencing this relationship are briefly discussed. In particular a correction for the effect of variation in mass of the base on the translational entropy contribution is shown to improve the AH/AS correlation slightly. In part 3 we reported thermodynamic and spectroscopic data for the association through hydrogen-bonding of thiocyanic acid with several open-chain and ring ethers.In this paper the results for the 1 1 hydrogen-bonded complexes between HNCS and a series of weak bases including sulphides selenides nitriles and aromatic hydrocarbons are described. EXPERIMENTAL A.R. carbon tetrachloride was dried over phosphoric oxide and distilled before use. Carbon tetrachloride solutions of WNCS - lov2 M) were prepared under anhydrous conditions as described is previously. Di-n-propyl selenide and di-n-butyl selenide were prepared3 by slow addition of the corresponding alkyl halide (1 mole) to a mixture of sodium formaldehyde sulphoxylate sodium hydroxide powdered selenium (1 mole) and water at 50°C. The reaction was completed by refluxing for 1-3 h. After addition of water the mixture was extracted with petroleum ether (b.p. 60-80°C). After drying and removal of solvent purification was achieved by fractional distillation (b.p.PrzSe 159"/760 mm ; b.p. n-Bu2Se 92"/22 mm). Hexamethylbenzene and hexaethylbenzene (Aldrich) had melting points of 164-5-1 65.6" and 129.5-1 30°C respectively (literature values 165°C and 128.7-1294") and were used without further purification. The cyclic sulphides were the gift of the American Petroleum Institute U.S. Bureau of Mines Laramie Wyoming. The remaining sulphides the nitriles and nitromethane were the best grades commercially available. They were dried over molecular sieves 4A and fractionally distilled. Purity was checked by vapour phase chromatography. * present address Dept. of Chemistry Girls College of Education AI-Menya Upper Egypt. t present address Dept. of Chemistry Monash University Victoria Australia.41 42 SPECTRA OF THIOCYANIC ACID Equilibrium quotients for association i.e. expressions in terms of concentrations instead of activities were found as described previously from the intensities of the NH absorption at 3469 cm-l of unbonded HNCS using a Perkin-Elmer model 21 spectrometer (LiF optics) and a Research and Industrial Instruments Co. variable temperature cell fitted with Infrasil windows. Enthalpy and entropy changes were calculated from equilibrium quotients at four temperatures -20 0 20 and 40°C. Each equilibrium quotient is the average of at least three separate determinations. The enthalpy and entropy values so calculated should properly be called apparent enthalpies and apparent entropies since concentrations instead of activities were measured.However in part 3 we reported agreement within the quoted limits of error between spectroscopically determined enthalpies and calorimetrically deter- mined enthalpies for those cases where both methods were used. RESULTS AND DISCUSSION Thermodynamic functions for the association of HNCS with base €3 HNCS + B+B HNCS where B = sulphide selenide nitrile etc. in carbon tetrachloride solution at 25°C are given in table 1 along with Avl and Avz the frequency shifts of the N-H stretching and the NCS pseudo-antisyinmetric stretching vibrations respectively. Estimated errors are indicated. No evidence for other than a 1 1 association was found with the possible exception of the nitriles. ENTHALPIES OF ASSOCIATION Table 1 shows that with the exception of di-t-butylsulphide the enthalpy changes for all the sulphide systems fall in the narrow range 303-3.7 kcal mole-l.Sulphides are clearly weaker hydrogen-bond acceptors than corresponding ethers.l This is expected in view of the lower electronegativity of sulphur (Pauling value 2.5) as compared with oxygen (3.5). Other workers 5 * ti have found substantially lower -AH values for the phenol + sulphide systems than for phenol + ether systems. Table 2 compares -AH" values for some HNCS and phenol complexes with sulphides and ethers. While - AH" values for the phenol + ether systems are ca. 1 kcal mole-I less than for the corresponding HNCS +ether systems in line with the higher acidity of HNCS the reported -AH" values for phenol+sulphide complexes are about the same or even larger than the HNCS+sulphide values found in this work.The - 25 % higher -AH" for the HNCS + di-t-butylsulphide complex compared with the HNCS + di-n-butyl sulphide complex reflects the greater inductive effect of the t-butyl group. Again the -28 % increase in - AHo found on replacing diethyl sulphide by di-t-butylsulphide may be compared with the ~ 2 0 % increase previously noted for the oxygen analogues. The enthalpy of formation of the 4-membered ring sulphide complex is significantly lower than for the open-chain sulphide and the other ring sulphide complexes as is the case for trimethylene oxide but unlike the ether system,l no evidence was found for a ring-opening reaction. Measurements of the C13-H coupling constants for trimethylene sulphide indicate that the C-H bond has a relatively high s character (N 29 %) and approximate calculations indicate a Cs^C bond angle of 88*6" a value much smaller than the normal bond angle found in open-chain sulphides.In dimethyl sulphide e.g. the C k angle is 105".8 It seems reasonable therefore to attribute the lower - AHo found for the 4-membered ring sulphide to an increased s character of the hetero-atom lone pairs resulting from ring strain. Lippert and Prigge have previously reached similar conclusions for phenol +ring sulphide complexes, T. M. BARAKAT J. NELSON S. M. NELSON A . D. E. PULLIN 43 The selenides appear to be proton acceptors of similar strength as the sulphides and this is in agreement with the findings of West et aL5 for the phenol system. Sulphur and selenium have almost the same electronegativity 2.5 and 2.4 re~pectively.~ TABLE 1 .-THERMODYNAMIC DATA (25°C) AND SPECTROSCOPIC SHIFTS HNCS+ compd MezS MeS Et n-Bu2S EtzS ES S 11 \ / S i s' n-BuzSe n-PrzSe CH3CN PhCH2CN EtSCN EtNCS hexaethylbenzene hexamethylbenzene mesitylene nitromethane -AG&*02 (kcal mole-1) 0.61 0-57 0.67 0.65 0.86 0.58 0.56 0-42 0.35 0.44 1-46 fa03 1.35 f-03 1.21 fa03 0.04 f.03 0.52 0.26 - 912 0-49 - A H i * 2 0 (kcal mole-1) 3-48 3.47 3-49 3.59 4.48 3.69 3.62 3.28 3.67 3.54 4.55 f *25 4.53 1-25 4.32 f *25 2.28 f a 2 5 3.57 3.05 2-30 3.15 -AS&-7 (cal deg.-l mole-1) 9.65 9.74 9.45 9-85 12.18 10.43 9.95 9-60 11.15 10.40 10.40 10.54 10.45 7-52 10-2 9-36 7-6 9.03 AVl (an-') - 380 f20 - 390 520 -400 f20 -400 f20 -4403I20 -4400f20 -420f20 - 383 420 - 410 k20 - 400 f20 -280 A10 - 284 f 10 *a *a ;:75 f 10 -216f15 - 170 f5 - 170 f 5 - 145 f10 + 124 A5 *obtained by extrapolation of observed wave numbers to infinite dilution.TABLE 2.-AHzSs FOR PHENOL AND THIOCYANIC ACID WITH BASES acceptor n-BuzS n-BuzO EtzS Et20 l2 tetrahydrothiophene tetrahydrofuran n-BuzS+ p-chlorophenol 32 n-BuzO + p-chlorophenol 32 -AH$hOH -AH%NCS kcal mole-1 kcal mole-1 4-19 5-71 3 -4 4.6 3.4 4.3 3.7 5-4 3.59 6-45 3-49 6-26 3-62 6-33 3-59 6-45 AYZ (cm-1) +16f4 + 15 1 4 +17f4 -1- 17 4-4 + 18 &4 +1744 + 15 f 4 ?:6 f 2 +35f2 +31&2 + 1 5 f 4 + 1 0 f 4 +6&4 +22&3 *a $00 The effect of electronegativity is further shown by comparing the results obtained for ethyl thiocyanate and ethyl isothiocyanate. For the thiocyanate complex in which the proton acceptor is presumably the terminal nitrogen atom -AH" is almost twice that for the iso-thiocyanate in which the terminal atom is sulphur.44 SPECTRA OF THIOCYANIC ACID However in both cases it seems that the basicity of the proton acceptor atom has been lowered by participation in the n-system of the NCS group. Thus for HNCS + EtNCS -AH" is only 2-28 kcal mole-l well below the values found for aliphatic sulphides. These results further demonstrate the importance of the hybridization of the proton acceptor atom. For the series of aromatic acceptors investigated both - AGO and -AH" increase in the order mesitylene < hexamethylbenzene(HMB) c hexaethylbenzene(HEB). For electron acceptors such as I2 and ICI association constants are much less for WEB than for HMB.1° While this is sometimes considered a consequence of a hyper- conjugative effect of the methyl hydrogens most workers attribute it to a steric effect.ll The fact that the observed enthalpy change for hydrogen bonding to HNCS reflects the accepted order of increasing inductive effect in these substituted aromatic hydrocarbons conforms with the low steric requirement of HNCS for hydrogen bonding noted in part 3.West l2 has found an increase in -AH" for phenol + alkylbenzene systems on passing from mesitylene (2.19 kcal mole-l) to durene (2.25 kcal mole-l) to HMB (2.46 kcal mole-l) but there have been no previous thermodynamic measurements on HEB as proton acceptor. As an example of polar hydrogen bond acceptors nitromethane was investigated together with two nitriles. Nitro-compounds have been classed as weak hydrogen- bond acceptors by Schleyer , and co-workers on the basis of shifts in the phenol vOH of less than 100 cm-l but no enthalpy measurements have been reported.With HNCS we observe a shift inv of 145 cm-l and -AHo of 3.15 kcal mole-l comparable with those obtained for alkyl substituted benzenes. It has been reported 13* l4 that hydrogen-bond shif'ts for nitriles and nitromethane are strongly concentration dependent. While Avl for the HNCS+CH,NO system does not vary with con- centration in the range 0-5-5 M CH3N02 Av ,for HNCS + CH3N is concentration dependent. The value of Avl given in table 1 was obtained by extrapolation to infinite dilution. No significant variation of Avl with concentration was found for other acceptors. For both nitriles there appears to be a slight dependence of association constant on concentration. Larger limits of error in -AH" are quoted for the nitrile complexes (table 1).Both acetonitrile and phenylacetonitrile are moderately strong hydrogen-bond acceptors. The observed -AH" of -4.5 kcal mole-l may be compared with the values 4*3,15 4-2 l 6 and 3.2 l7 reported by others for the phenol+CH,CN system. It seems that the basicity of the nitrile function is slightly greater in these compounds than in ethyl thiocyanate. The nitrile frequency vCEN shifts to higher values by 11 to 12 cm-l on hydrogen- bonding (see also part 1 ref. (2). An increase in vC-N on Lewis acid-base interaction is quite general ''9 l9 and has been discussed by several authors.20* 21 The more usual effect of hydrogen-bonding on the spectrum of the base is to shift to lower frequency the vibrational modes involving motion of the proton acceptor atom,2 as for ethers and carbonyl cornpo~nds.~~.In the sulphides examined absorptions involving C-S motion shift to lower frequencies by -10cm-l on bonding but accurate observation of the shift was made difficult by the presence of a large excess of free sulphide. We did not observe any change in the spectrum of the aromatic hydrocarbons on complexing. AH"/Av c 0 R R E LA T 10 N s It is important to test how far the empirical Badger-Bauer correlation 22 of -AH" with Avl holds because estimates of the strengths of hydrogen-bonds are often made from data on spectroscopic shifts. The results given in table 1 for the T. M. BARAKAT J . NELSON S. M. NELSON A. D . E. PULLIN 45 interaction of a varied selection of bases with a single proton donor allow a useful test of the generality of the Badger-Bauer relationship to be made.Fig. 1 shows that there are many exceptions to the empirical rule. For example on the basis of shifts in v1 the sulphides would be expected to be stronger proton acceptors than are the nitriles while the thermodynamic measurements show that the reverse is true. This behaviour may be accounted for at least in part by supposing that for non- polar bases the energy of interaction is predominantly due to the hydrogen bond but with polar bases such as nitriles other interactions such as direct electrostatic inter- action between the polar base and the NCS portion of the HNCS molecule are appreciable. An indication of the magnitude of the latter could be expected from 0 0 - + ++ >k X 0 P 1 100 300 500 700 AV cm-l FIG.1.-Plot of AH" against Av for HNCS-+base system. (0 ethers ; 0 open-chain sulphides ; cyclic sulphides ; x nitriles ; + aromatics ; 4 nitromethane). the shift in v2 the higher of the two NCS stretching frequencies. The absorption due to this mode diminishes in intensity and increases in frequency on hydrogen bonding i.e. v2 moves towards the frequency of the free NCS- ion which for KNCS in aqueous solution23 occurs at 2066 and at 2053cm-l in KBr.24 Fig. 2 shows there is no simple relation between Avl and Av2. However for bases of low polarity such as sulphides and some aromatic hydrocarbons the fractional decrease in the N-H force constant f on bonding (fir,=,-fbonded)lfffree obtained from the ratio (v free-v bonded)/vf free approximates to A V ~ / ( V ~ ~ ~ - -vZfree) i.e.to the fractional change of vz towards the ionic frequency of 2066 cm-l indicating mainly ionic-type structures (2) and (3) to be important in the resonance forms for the complex * + (1) B H-NCS (2) B-H NCS (3) B NCS + (4) B H-NEC-S. *Charge transfer to give B+HNeS may also be signiikant. 46 SPECTRA OF THIOCYANIC ACID On the other hand for the nitromethane and nitrile complexes only half the change in v2 can be accounted for in this way (see table 3). This suggests that in these cases additional polarization of the HNCS molecule occurs on hydrogen-bonding which results in a further increase in v2. Simple electrostatic calculations (appendix 1) 600 * 400 E 1 0 -I a' 2 oc 0 0 0 g x xx 0 + + + c I I I 20 LO 60 Av cm-l FIG. 2.-Plot of Av against Avz (symbols as for fig. 1). TABLE 3 ffree-fbonded Av2 proton acceptor ffree V~NCS - - ~ r e e dimethyl sulphide methyl ethyl sulphide di-t-butyl sulphide pentamethylene sulphide tetrahydrothiophene t rimet h ylenesulp hide di-n-butyl selenide benzene mesitylene hexamethylbenzene hexaet h ylbenzene diethylether tetrahydropyran tetrahydro furan phenyl acetonitrile acet oni trile ethyl thiocyanate nitromethane *18 -20 -23 *2 1 -22 *2 1 -22 *04 -07 ~ 0 9 -09 -28 -29 -29 -10 -10 -10 -08 *19 -18 *20 -20 -2 1 -20 -18 -04 -06 -1 1 -18 -4.4 *46 -47 -42 -4 1 -36 a26 show that it is reasonable to attribute the larger Av2 for bonding to polar bases to polarization of HNCS towards structure (4) by the dipole field of the base.However although the envisaged polarization towards structure (4) is supported by the observed shifts in v2 the calculations given in appendix 1 refer only to a part (and probably T .M . BARAKAT J . NELSON S . M . NELSON A . D . E . PULLIN 47 the smaller part) of the electrostatic interaction between the polar base and HNCS viz. that part arising from the CH3CN dipole + HNCS induced dipole interaction. This amounts to about 0.3 kcal mole-l. It is not possible to estimate the electrostatic interaction between the base dipole and that of the NCS part of the HNCS molecule since insufficient is known about the charge distribution in the latter. Another failure of the AHo/Avl correlation is apparent from the results for HMB and HEB. Hydrogen-bonding to these leads to shifts in v1 of 170+3 cm-' in each case although there is an appreciable difference in -AH" (3.05 and 3.57 kcal mole-' for HMB and HEB respectively).The two compounds are further differentiated by the greater half-width of the v1 band for the HMB complex (92+ 5 cm-l) than for HEB (72 & 5 cm-I). AH"/AS" C 0 RRE L AT I 0 N Fig. 3a is a plot of -AH" against -ASo ; it includes data for the HNCS +ether systems reported in part 3. Although with considerable scatter there is a linear relation between -AH" and -AS" similar to that observed for straight-chain ethers (part 3) and observed for numerous other association equilibria. The nitriles and ethyl thiocyanates show greatest deviation in the sense of a smaller than usual entropy decrease on complex formation. Various factors dependent on molecular details such as mass moments in inertia vibrational frequencies etc. affect AH" and AS" in different ways and though there are reasons for expecting a rough correlation between AH" and AS" as is commonly there can be no exact general relation which is independent of molecular details.Consideration of solution equilibria is further complicated by ignorance of the important low frequency motions in solution. In order to assess at least approximately the effect of mass we have corrected the observed AS" values to allow for the varying masses of the base molecules. By use of the expression for the translational entropy of gas phase molecules the observed ASo values are converted to mass-standardized AS;.,. values which refer to the entropy change for a molecular weight of 100 for the base molecule. Details of the procedure are given in appendix 2. For proton acceptors of molecular weight less than 100 the values of -AS" are increased e.g.for CH,CN the lightest base studied the observed - AS" is 10.40 and -AS&. is 11-68 cal/mole deg. For the base molecules of molecular weight greater than 100 the -As0 value is decreased e.g. for HEB -AS" = 10.20 and -AS&. = 9-46 cal/mole deg. The effect of these corrections is shown in fig. 3b which also includes seven points for the HNCO+ base system corrected to standard masses of 59 (i.e. to that of HNCS) and to 100 (standard base mass). In fig. 3b the abscissa has been displaced for clarity. Comparison of fig. 3" and 3b indicates that the correlation between -AH" and -AS" is slightly improved after correcting for mass differences. This is supported by a least squares analysis. Deviations of the observed - AS" values from the least-squares straight line of -AS" against -AH" for hydrogen bonding by HNCS were calculated for the following four cases (a) -ASo (observed) against - AH" for 10 non-cyclic ethers (those of table 1 part 3) ; (b) - against - AH" for the same 10 ethers ; (c) - ASo (obs.) against -AH" for these 10 ethers and the other 18 bases of table 1 of this paper ; (d) - ASSqM.against - AH" for the same 28 bases as in (c). Root-mean-square deviations of -AS" in cal deg-l mole-1 were (a) o-45 ; (6) 0-4* ; (c) l e l ; (d) 0*50. A considerable part of the improvement for ( d ) compared with (c) is due to the raising of the -AS" values for the light bases CH3CN and diethyl ether towards the least squares line and the lowering of points for the heavy molecules n-Bu,Se and t-Bu,S 48 SPECTRA OF THIOCYANIC ACID towards the least squares line.The points for ring ethers were not included in the least squares calculations as these fall markedly below the best line through the other points. Ring sulphides are not distinguished from other sulphides in this way in either fig. 3" or 3b. Fig. 3b shows that the - ASssM. values for the HNCO +base system fall close to the best line for the HNCS +base points the uncorrected -AS" values fall mostly below the line. Root mean square deviations of -AS" (obs.) and -AS&. for the HNCO+base system from the corresponding least squares lines for the HNCS+base systems (cases (c) and (d) above) were 1.2 and 0-71 cal deg? mole-l. dih O / k . / ' 2" 4 6 a -AH" (kcal mole-') 26 22 cn 18 Q I I4 10 FIG. 3.-Dlot of -AHo against -ASo.(Symbols as for fig. 1 ; 0 cyclic ethers+HNCS A HNCO+bases). The slight improvement of the correlation of -ASo with -AH" when AS8.M. rather than ASo (obs.) values are used in the above cases suggests that the correction from -AS" (obs.) to AS&. removes a part of the variation of -AS" which is not related to a corresponding variation in - AH". APPENDIX 3 An estimate of the polarization of HNCS by the dipole field of CH&N is required. For the present purpose it seemed most appropriate to calculate the component of the induced moment in the -NCS moiety of the molecule parallel to the -NCS axis. For this the component of the field parallel to -NCS due to the CH3CN dipole was calculated by elementary electrostatic considerations 36 and the product of this with the principal component of the polarizability parallel to the -NCS axis taken to give the required T .M. BARAKAT J . NELSON S. M. NELSON A . D. E. PULLIN 49 induced moment. In the absence of experimental values assumptions had to be made about the geometry of the complex and the polarizability of -NCS. These were that the H-N bond in HNCS was co-linear with symmetry axis of CH3CN and that the N . . . N distance was 3.0 A (this is the distance obtained by application of AVHN-N . . . N distance correlations 27) and that the polarizability components of -NCS were equal to the mean of those of CQ2 and CS2. The calculated induced moment is sensitive to the location of the equivalent point dipole of CH,CN. For the point dipole located at the centre of the C =N bond of CH3CN and the polarizability elipsoid centred at the mid-point of N-C-S the calculated induced moment in -NCS for a dipole moment of CH3CN of 3-92 D is 0.65 D.If the point dipole of CH3CN is located at the nitrogen nucleus of CH3CN the induced moment is 1.3 D. A lesser difference results from using bond polarizabilities centred on the N-C and C-S bonds instead of an -NCS group polarizability centred at the mid-point of The change in the frequencies of the stretching modes of -NCS of HNCS can be related to the polarization of HNCS with the following additional assumptions. (a) Polarization of HNCS is interpreted as incursion of the resonance structure H-N=C-%. (b) The structure H-NsC-S would have a dipole moment 10 D greater than that observed for HNCS. (c) The induced moment and force constants changes vary linearly with H-NEC-S character induced.(a) The stretching force constant of N-C and C-S in the molecule HNCS and in the resonance structure H-N = C-3 may be taken to have the following values in HNCS 13.4 and 7.3 mdyne/A (after Thomas 28) ; in H-N = C-5 19.3 and 3.9 mdyne/A (from the value of -NrC- in the dimethyl nitrilium ion l9 and the mean of the values of C-S- in CH&H and CF3SH.29) The changes of the frequencies of the stretching modes of -NCS were calculated from the differential changes of the sum and products of the roots 30 21 and A2 (A = 4z2c2v2 v in cm-l) with the change of the primary force constants in a linear triatomic system. The interaction stretching force constant was assumed to remain unchanged.* For an induced moment of 0.65 D corresponding to changes in the N-C and C-S force constants of 0.384 and - 0-221 mdynes/A the changes in the frequencies of the stretching modes of -NCS for initial frequencies of 1981 and 850 cm-l were calculated to be + 19 and - 7 cm-l respectively.The energy of polarization (1) of -NCS plus interaction of the resulting induced dipole with the polarising field of CH3CN was taken to be - + ( E k x + E?a,+ EZ2aZz) where a, = a,,, are the principal components of the polarizability of -NCS perpendicular to NCS; azr is the polarizability parallel to NCS and Ex etc. are the components of the field in these directions. The value of the net energy of polarization corresponding to an induced moment of 0.65 D is -0.36 kcal/mole. -N-CQ. + + + i- + + APPENDIX 2 For the hydrogen bonding equilibrium in carbon tetrachloride solution HNCS + B fB HNCS (1) we write t *Ham and Willis show that the differing stretching frequencies of the N C S group in CHsNCS NCS and HNCS can be accounted for by varying the NC and CS interaction stretching constants the primary stretching constants remaining the same.However in the absence of indications to the contrary we assume that changes in the primary force constants are responsible for the frequency changes in the present instance. ?The superscript O indicating standard states is omitted in this section. 50 SPECTRA OF THIOCYANIC ACID where dsobs is the observed value of the standard entropy change for (l) AStr is the trans- lantional entropy change and ASrem the remainder and where the dependence of AStr on the molecular masses is the same as in the gas-phase reaction.For one mole of gas S = +R In M+S* where M is the molecular weight and S* is a quantity that depends on volume temperature and fundamental constants and conversion factors and is independent of the molecular weight of the gas. Then for (l) A& = @ In [(MB+ MHNCS)/(MBMHNCS)l- s" (3) If we wish to refer the AS to the value for a particular molecular weight of B M we can write using an obvious notation Thus the differences of AStr for different masses B depend only on the mass of B and Mmcs. We assume that differences of translational entropy defined above have some relevance to equilibrium (1) in solution. Using (2) and the identity = Astr(Mg) - Astr(M*)19 we obtain AS0b.s- [Astr(MB) -Astr(M;)] = Astr(Mg> + Asran- ( 5 ) Since we suppose that the quantity on the r.h.s.of ( 5 ) may be more directly related to the observed A H values for (1) than ASobs it is convenientto define an entropychange &.M. for (1) for a standard mass M* by the 1.h.s. of ( 5 ) which is defined exactly in terms of quantities experimentally known Ass.,. = ASobs - [ASJMd - Astr(M31 (6) Values of A&,M. were calculated from ASobs and the molecular masses using (4) and (6) with Mg = 100. Values of -ASS.M. are plotted against -AH in fig. 3(b). We have only taken the masses of B into account in the translational part of the total entropy change and not in AS,,, and the calculations depend on the assumption noted above for the dependence of Str on M. The volume of the system does not enter into the calculations however as long as it remains constant. For the equilibrium HNC0-t B $B HNCO (7) ASS.M.values were calculated by an extension of the above procedure to correct to a standard molecular weight Mg = 100 and also to correct from the molecular weight of HNCO to a molecular weight of 59 (that of HNCS) in an attempt to obtain values ASS.M. for (7) more directly comparable to those for (I). T. M. Barakat M. J. Nelson S. M. Nelson and A. D. E. Pullin Trans. Farday SOC. 1966 62 2674. T. M. Barakat N. Legge and A. D. E. Pullin Trans. Faraday SOC. 1963,59 1173 1764. M. L. Bird and F. Challenger J. Chern. Soc. 1942 570. L. Pauling Nature ofthe Chemical Bond (Cornell University Press Ithaca N.Y. 1960) p. 93 R. West D. L. Powell M. K. T. Lee and L. S . Whatley J. Arner. Chem. Soc. 1964 86 3228. T. Gramstad and W. J. Fuglevik Acta Chem. Scand. 1962,16,2368.' E. Lippext and H. Prigge Ber. Bunsen Ges. 1963 67,415. T . M. BARAKAT J . NELSON S . M . BELSON A . I). E . PULLIN 51 L. E. Sutton Interatomic Distances (Chem. SOC. Spec. Publ) no. 11 1958. E. Lippert and H. Prigge Annalen 1962 659 81. M. Tamres D. R. Virzi and S . Searles J. Amer. Chem. Soc. 1953 75,4358. lo G. Briegleb Electronen-Donator-Acceptor Komplexe (Springer Verlag Berlin 1961). l1 L. J. Andrews Chem. Rev. 1954,54 754. l2 R. West private communication. l3 W. F. Baitinger P. von R. Schleyer T. S. S. R. Murty and L. Robinson Tetrahedron 1964,20 l4 A. Allerhand and P. von R. Schleyer J. Amer. Chem. Soc. 1963 85,866. l 5 D. L. Powell Diss. Abstr. 1962 23 1207. l6 H. Dunken and H. Fritsche 2. Chem. 1961,1 127. l7 M. D. Joesten and R. S. Drago J. Amer. Chem. Soc.1962 84 3817. l8 T. L. Brown and M. Kubota J. Amer. Chem. Soc. 1961,83,4175. l9 G. C. Turrell and J. E. Gordon J. Chem. Physics 1959,30 895. 'O S. C. White and H. W. Thompson Proc. Roy. SOC. A 1966,291,460. 21 K. F. Purcell and R. S. Drago J. Amer. Chem. Suc. 1966,88,919. 22 R. M. Badger and S. H. Bauer J. Chem. Physics 1937,5 839. 23 L. H. Jones J. Chem. Physics 1966,25 1069. 24 P. 0. Kinell and B. Strandberg Acta Chem. Scund 1959 13 1607. 25 W. B. Person J. Amer. Chem. SOC. 1962,84 536. 26 C. J. F. Bottcher Theory ofEIectric Polarisation (Elsevier Amsterdam 1952) pp. 9 62 and f 7 G. C. Pimentel and A. L. McClellan The Hydrugen Bond (Freeman London 1960. 28 W. J. 0. Thomas J. Chem. SOC. 1952,2383. 29 R. E. Dinniny and E. L. Pace J. Chem. Physics 1959,31 1630. 30 G. E. Herzberg Infra red and Raman Spectra (Van Nostrand N.Y. 1945) p. 173. 31 N. S. Ham and J. B. Willis Spectrochim. Acta 1960,16,279. 32 I. M. Ginsburg 7th European Congr. Mol. Spectr. (Budapest 1963). 1635. 126.

ISSN:0014-7672    

DOI:10.1039/TF9696500041

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Detection of the Cyclopropane Ring and its Degree of Substitution in Long-Chain Fatty Acid Esters by Infra-red Spectroscopy BY P.TORKINGTON The Wellcome Research Laboratories Beckenham Kent Received 14th May 1968 Inclusion of the cyclopropane ring in long-chain fatty acids during incubation of adipose tissue in the presence of sodium cyclopropanecarboxylate has been proved to occur from measurements on the CH-stretching region of the infra-red spectra of ester samples obtained by chromatographic analysis from the reaction products. The frequencies of the non-paraffinic absorption and the intensity relative to that of the paraffinic absorption show the system present to be a 1,1,2,3-tetra- substituted cyclopropane such as is found in naturally-occurring cyclopropanes e.g. pyrethrins. The cis-cod?guration is probably favoured.The proportion of cyclopropyl corresponds to about one ring per chain of fifteen methylene groups this conkning the result suggested by radio-carbon counts. As a result of investigations by other workers in these laboratories it was suspected that the cyclopropane ring was incorporated into long-chain fatty acids during incuba- tion of adipose tissue in the presence of sodium cyclopropanecarboxylate. It was required to collfirm this using infra-red spectroscopy. The present paper deals with the spectroscopic problem. Biochemical procedures and results will be reported elsewhere. Detection of cyclopropyl systems by chemical spectroscopy dates from 1946 when a pair of skeletal C - 4 frequencies at 886,1026 cm-l was said to be characteristic of trisubstituted cyclopropanes.2 In 1949 the 3 p region was said to be ~uitable.~ Since then both regions have been investigated frequently in an attempt to make unambiguous identification of cyclopropane systems possible by inf'ra-red spectro- scopy.The position has finally become accepted as follows. (1) Identification by vibrations characteristic of the triangular C-C system is not possible in molecules of any complexity because so many other modes are liable to lie in this region of the spectrum ; in particular esters absorb strongly just where the most characteristic vDc occurs at N 1020 cm-l. (2) Identification by vibrations characteristic of C-€3 bonds attached to the cyclopropane ring is much more feasible but is only completely reliable in the absence of olefinic and aromatic C-H.The ring strain in 4- and 3- membered rings leads to an approach towards olefinic C-H character in the attached C-H bonds but the ranges of frequencies occupied by each group all overlap. Mono-substituted cyclopropanes have been most studied. Of sixty compounds covered in 1960,4 all showed a pair of bands lying within the two regions 2995-3033 and 3072-3099 cm-' ; in an earlier study,5 3012 and 3096 cm-1 had been given as mean values. Now the pair of bands undoubtedly comes from the pair of frequencies allowed any CH2 group ; in the paraffins the ranges are 2830-2850 and 2910-2960 cm-l. The higher member of the pair is important because its absence means absence of CH2 ; in a study of 1962,6 all cyclopropanes containing ring-CH were found to have a band in the region 3070-3100 cm-l except where there was masking from -COOH and -CONH2 absorption.52 P. TORKINGTON 53 For cyclopropanes which have only odd C-H bonds identification becomes more difficult ; the intensity of vCH absorption is much less than for vCH2 principally because of the smaller number of C-H bonds and also the bands are less sharp. The earliest example of such a compound was the terpene car-3-ene (I) which shows inflections to the vCH absorption region at -3000 and -3070 cm-1 ; probably one of them is due to olefinic and the other to cyclopropyl C-H. In ref. (6) in which 42 compounds are listed frequencies for six containing only odd C-H bonds are given unsaturation and fused rings being absent ; they all have a band in the region of 2995-3020 cm-l. R" causes shifts the trans-isomer cis-trans-isomerism in the structure R' )< R R absorbing at the lower end of the frequency range the cis- at the higher.Other papers on the subject are listed in ref. (8)-(14). EXPERIMENTAL Adipose tissue from freshly-killed rats was incubated at 37"C usually for 3 h according to a standardized biochemical procedure (see ref. (1)). The fatty acid methyl esters obtained from the fats isolated were subjected to gas-chromatographic analysis and it was arranged that fractions could be taken from the column as desired. With 14C in the initial carboxylate ion a radio-carbon-count maximum was obtained in the palmitate region and this was taken as evidence for the cyclopropane carboxylic acid having become associated with a carbon chain of about 15 units. The quantities of ester coming over were too small for examination in normal liquid cells.The technique used (developed previously in these laboratories) was to collect samples in Teflon tubes of size 1 x 20 mm plugged with cotton wool and con- taining -5 mg of spectroscopic potassium chloride. The salt plus absorbed ester was then made into a micro-disc N 5 x 1 x 1 mm in a slot cut in a previously-pressed KCl disc. This disc was mounted in a beam condenser giving a linear reduction of image size of 1 5 at the focus which fitted into the sample cell-well of the Unicam S.P. 100 spectrometer used for obtaining the spectra over the range 650-3650 cm-I. A beam-attenuator in the reference cell-well was used for compensation of energy lost by the beam-condenser and by scattering. When the latter is bad more is lost than gained by compensating fully since the response of the instrument becomes sluggish as the energy falls and a higher gain with associated " noise " becomes necessary; a compromise must be made.Sometimes a more useful spectrum is obtained with low compensation for scattering ; the absorption-region then appears " squashed ". RESULTS AND DISCUSSION PRELIMINARY CONSIDERATION OF RESULTS FOR THE FATTY ACID ESTER SAMPLES The spectra were all typical of a fatty acid ester and showed the long-chain absorption l5 at -720 cm-l. The only point of interest outside the vCH region 54 DETECTION OF CYCLOPROPANE RING I N ESTERS relevant to the present problem concerned the varying degree of resolution of bands in the region 1200-1350 cm-l. Crystalline compounds give l6 a series of sharp bands here whose number increases with chain-length.Some of the samples gave such bands others did not ; broadly they could be classed as liquid semi-crystalline and crystalline. (The long-chain absorption at - 720 cm-l also varies with physical state resolving into a pair of sharp peaks in the crystal and this was observed also.) The phenomenon is relevant to the detection of cyclopropane rings in the vCH region since the more crystalline the sample the more readily visible will be any inflections to the principal absorption from paraffinic C-H ; one sample might at first sight appear to contain more cyclopropyl than another when in fact the inflections were merely sharper in the more crystalline sample. In all ten runs were examined. Control of the quantity of ester collected in the sample tubes was not feasible ; ideally the vCH region gave absorption of N 95 % at the principal maximum at 2960 cm-l and then inflections and sometimes small peaks were visible on the high-frequency side running down the side of the band from - 70 % absorption.With too much sample the presence of non-paraffinic C-13 could usually be confirmed but no exact location of inflections was possible ; with too little sample the subsidary bands were too weak to show even though the principal absorp- tion was more confined. Another feature which complicated interpretation of the spectra was occurrence of scattering to varying extents in different samples. Long-chain compounds do not in general form ‘‘ good ” KC1 discs and considerable scattering causing rising back- ground through the vCH region is to be expected.The variation in degree of crystal- linity noted above accounts for variation of scattering from sample to sample. Relevant data from the vCH bands of the four most favourable samples are summarized in table 1. TABLE 1 sample 1 2 3 4 nature of non-paraffinic single broad but inflect ion absorption continuous inflections definite and inflection maximum maximum absorption maxima 2990-3030 2990( ?) 3007 2990 3020 3022 (max.) state of sample liquid liquid liquid crystalline If no unsaturation is present these results give proof of the existence of cyclo- propane rings in the ester(s). Further since even when there are definite maxima visible there is no trace of absorption in the region of higher frequency -3070- 3100 cm-l there cannot be any cyclopropyl CH groups ; only odd C-H bonds are present on the rings.Lastly since absorption over the region 2990-3030cm-l appears to become more definite at the higher-frequency end the presence of cis- pairs 4,H-CH- is probably favoured relative to trans. UNSATURATION No bands assignable to vc=c or aromatic character were detectable in the spectra but to confirm absence of unsaturation attempts were made to remove the non-paraffinic CH absorption by catalytic reduction of the esters before chromato- graphic separation. Two sets of conditions were employed. Under relatively mild reduction only the unsaturation should vanish while stronger reduction should in addition open the cyclopropane rings. Samples R1, were examined which had been P. TORKINGTON 55 obtained following application of each of these sets of conditions and both spectra still showed non-paraffinic vCH absorption of the same order of intensity as observed for the unreduced esters.(The reduced samples were semi-crystalline and both showed inflections at 2990-2995 and 3020-3025 cm-l). Therefore there can be no appreciable amount of unsaturation and further the cyclopropane ring here is abnor- mally resistant to attack by reduction. Now such resistance has been observed previously with highly-substituted cyclopropanes ; chrysanthemic acid COOH will only take up 1 mole of hydrogen this saturating Me2c=cHX Me Me the C=C. The resistance to reduction observed in the present samples is suggested to be consistent with the finding of only odd C-H bonds attached to the rings. APPROXIMATE QUANTITATIVE ANALYSIS No accurate estimation was aimed at ; the extinction coefficients for v ~ - ~ vary Is with chain-length in paraffins and the non-paraffinic absorption in the present samples is intractable to treatment by conventional methods.What was attempted was an estimate of the (mean) number of C-H bonds present on each ring so that the basic system present could be stated to have one two or three such bonds ; also an estimate o f the size of the whole paraWc residue. Both these pieces of information can be extracted simultaneously by comparing the absorption-areas of non-paraffinic and paraffinic C-H in the vCH region; the areas were traced from the spectra cut out and weighed. The results for four substances containing cyclopropane rings are given in table 2 together with an olefinic compound for comparison.TABLE 2 linoleic acid A-ketone 0.994 mix 1.48 mix 1-93 mix ratio of absorption areas C-H ratio non-paraffinic/ area ratio/C-H ratio *43 032 -34 -28 -29 non-paraffinic/paraffinic -064 -072 ‘0483 00594 00797 paraffinic ,148 *222 -142 -21 1 -276 NOz and the “ mixes ” are mixtures X A-Ketone is the compound CH3. CO Me Me of sodium cyclopropane carboxylate and stearic acid the number referring to the molar ratio. The C-H ratio is estimated from the total number of C-H bonds e.g. in the 1.48 mix it has the value 1-48 x 5/35. The last line in table 2 the area- ratio for unit C-H ratio is of the same order for all the cyclopropane derivatives being somewhat lower than the value for olefinic C-H. Area-ratios for the chroma- tographic samples are obtainable to within -20 %.They are given in table 3 for the four samples of table 1 and for the two “reduced” samples R1 following what should have been total hydrogenation and R hydrogenation of C=C only. TABLE 3 sample 1 2 3 4 Ri R2 ratio of absorption-areas non-paraffinic /paraffinic so25 a014 -03 1 -047 -020 -01 7 The values for R and R2 are effectively identical confirming the absence of any reducible cyclopropane rings. Sample 4 was obtained using a much higher concentra- tion of sodium cyclopropane carboxylate than customary to obtain proof of the entry 56 DETECTION OF CYCLOPROPANE RING I N ESTERS of the rings into the ester chains ; the high value of 0.047 shows an enhanced content of rings. Sample 3 was taken well away from the 14C activity maximum (and the high non-paraffinic C-H content is anomalous).Samples R1 and R are in fact only to be compared with samples 1 and 2. All lie in the range 0.020+0.006. 0.020 k0.004 represents the accuracy attainable so not more than a tenth of the non- paraffinic absorption is likely to be due to olefin. To estimate the cyclopropyl content of the samples if we take the area-ratio for a C-H ratio of unity as 0-32 then an area-ratio of 0.020 in a sample will correspond to a C-H ratio of 0*020/0.32 = 1/16. This could arise e.g. from a methyl ester in which there was one cyclopropane ring with two isolated C-H bonds associated with an aliphatic system of 15 carbon atoms ; which is very near the result required for the palmitate region of the chromatographic analyser and can be taken as almost proof that the principal structure involved is of type RI -X R,.(Tetrasubstituted cyclopropanes are common in nature e.g. the pyrethrins.) R3 R4 The author is grateful to The Wellcome Foundation for permission to publish these results. W. G. Duncombe and T. J. Rising Biochem. J. submitted. J. D. Bartleson R. E. Burk and H. P. Lankelma J. Apner. Chern. SOC. 1946,68,2513. E. K. Plyler and N. J. Acquista J. Res. Nut. Bur. Stand. 1949 43 37. S. E. Wiberley S. C. Bunce and W. H. Bauer Anal. Chem. 1960,32,217. S . E. Wiberley and S. C. Bunce ibid. 1952 24,623. H. Weitkamp U. Hasserodt and F. Korte Chem. Ber. 1962,95,2280. A. R. H. Cole J. Chem. SOC. 1954 3807. J. M. Derfer E. E. Pickett and C. E. Boord J. Amer. Chem. SOC. 1949,71,2482. M. L. Josien and N. Fuson Compt. rend. 1950,231 1511. lo M. L. Josien N. Fuson and A. S. Cary J. Amer. Chem. SOC. 1951,73,4445. l1 R. N. Jones P. Humphries F. Herling and K. Dobriner ibid. 1952,74,2821. l2 V. A. Slabey ibid. 1954 76 3604. l3 C. F. H. Allen T. J. Davis W. J. Humphlett and D. W. Stewart J. Org. Chem. 1957,22,1291. l4 M. Hanack H. Eggensperger and S. Kang Chem. Ber. 1963,96,2532. Is H. W. Thompson and P. Torkington Roc. Roy. SOC. A 1945,184,3. l6 ~ e e e.g. Chemical Applications of Spectroscopy vol. IX of Technique of Organic Chemistry (Interscience Publishers Ltd. London 1956) p. 346. l7 S. H. Harper J. Sci. Food Agric. 1954 5 529. lg see e.g. Chemical Applications of Spectroscopy p. 338.

ISSN:0014-7672    

DOI:10.1039/TF9696500052

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Studies in Regular Solution Theory Part 1 .-Solubility Studies of Tetraphenyltin in Simple Non-Polar Solvents BY M.VITORIA AND JOHN WALKLEY Dept. of Chemistry Simon Fraser University Burnaby 2 B.C. Received I 1 th December 1967 The solubility of tetraphenyltin in a number of non-polar solvents is presented. The data are analyzed in terms of Hildebrand's theory of regular solutions. The large molar volume of this solute requires the inclusion of a Hory-Huggins term in the saturation solubility equation. The possible limitation of the interaction-energy geometric-mean rule are examined and a comparison is made with data for the solubility of stannic iodide iodine and sulphur in a similar set of solvents. The theories of Hildebrand and of Scatchard have largely led to an under- standing of the thermodynamic properties of solutions of non-electrolytes.The success of regular solution theory lies in its interpretation of the properties of solutions in terms of the experimental properties of the pure components. The excess free energy PE of one mole of a regular solution may be written as where Fis the molar free energy of the solution and Pi the free energy of the solution if it were ideal. Vl and Vz are the molar volumes of the two pure components x1 and x2 their mole fraction in solution and +l and +2 the corresponding volume fractions. The constant k is a measure of the interaction energy of the pair of unlike molecules relative to that between like molecules. In the theory of solutions the square root of the cohesive energy density is termed the " solubility parameter " di and k = (6 - 62)2 ; (6 -a2) is an important self-consistent parameter in the theory.For the simplest solutions the solubility parameter difference term is related to the experimental saturation solubility by the equation where xi is the ideal mole fraction solubility. For a wide range of liquid-liquid and solid-liquid systems an excellent self-consistency in (8 - 8,) is f0und.l For systems exhibiting a disparity in the molar volume of the solvent and the solute some formulation of a Flory-Huggins-type of expression for the athermal mixing process must be developed. The solubility equation then involves a term reflecting the inequality in molal size from what is essentially an entropy consideration. Hildebrand has pointed out that in terms of free volumes the athermal entropy of mixing unequally sized species becomes FE = F-Fi = k4142(~1 V2 + ~2 VJ log X i = log X2 + V24:(61 - 62)'/2*303RT NIVlf ]+N,ln[ NzV ] N',Vf,+NzVi N,v',+N,v; - N1 In ASM R -- and that this reduces to the usual Flory-Huggins approximation if the free volumes Y are set proportional to the molar volumes of the components.In many reported cases the inclusion of a Flory-Huggins term does however improve the (6 -a2) consistency. Attempts to examine the need for the inclusion of the volume-disparity 57 58 REGULAR SOLUTION THEORY term in simple systems are mostly limited to those in which the solvent molar volume Vl is somewhat greater than that of the solute V,. This minimizes the effect of the (1- V2/Vl) term. In the present paper we examine the capability of a regular solution theory to interpret the behaviour of a large spherical solute molecule tetra- phenyltin (V = 314 cm3) dissolved in comparatively small ( V less than 120 cm3) solvent molecules.The criterion that the success of regular solution theory lies in the constancy of the solute 82 value obtained from solubility data is examined over the wide range of V2/V1 ratios. EXPERIMENTAL The tetraphenyltin was prepared by the method of Schlessinger.6 The crude product was recrystallized twice from benzene and melted at 229"C (lit. m.p. 229°C). Molecular weight determinations and an analysis for the tin as stannic oxide ' confirmed that the com- pound was tetraphenyltin. Most of the solvents were of spectroscopic grade and were used without further purifica- tion. Dichloroethane and m-xylene were each distilled twice at 760 mm ; they boiled at 83.5 and 137°C respectively.Toluene was washed twice with one-tenth of its volume of concentrated sulphuric acid and then successively with water sodium carbonate solutions and water. It was dried over calcium chloride and distilled over sodium. Its b.p. was 110-6°C. To measure the solubility the solvent and excess tetraphenyltin were placed in 50ml flasks equipped with magnetic stirrers. Stirring was continued for 24 h and in order for all the suspended particles to settle a further 12 h were allowed to elapse. The temperature range over which the saturation solubility was measured was 20-40"C; the temperature was held constant to 0-01°C. The amount of tetraphenyltin present was estimated spectroscopically at 258 mp. The concentration corresponding to a given optical density was read off from a Beer's law plot obtained for cyclohexane solutions of known molarity.A number of the solvents were opaque in this region of the spectrum and so 1-2ml portions of their solution were evaporated to dryness and the residue re-dissolved in cyclohexane for spectroscopic analysis. The general consistency of the results confirmed the accuracy of this technique. For solvents which were transparent near 260mp direct determination as well as the above technique was used ; the results were in good agreement. In order to transform the experimental results into thermodynamical quantities the molal heat of fusion at 25°C and the molal volume of liquid tetraphenyltin extrapolated to 25°C are required. No literature values were found and so both were determined experimentally.A precision capillary tube was filled with a known weight of tetraphenyltin and heated in a glycerine bath. The level of the meniscus of the molten tetraphenyltin was determined using a cathetometer. The results extrapolated to 25°C gave a molal volume Vl or 314.4cm3. The molal volume of solid tetraphenyltin at 25°C is 284cm3. The molal heat AH; of fusion at the melting point was determined using a Perkin-Elmer DSC-1 differential scanning calorimeter calibrated with a sample of indium heated under the same conditions. A value of 8-9 kcal mole-' was obtained. The heat of vaporization is also necessary and was obtained from the equation of Hilde- brand based on the '' Hildebrand rule " according to which normal liquids should have the same entropy of vaporization at temperatures at which their vapours have the same molal volume AH; = -2950+23-7Tb+0-02T' = 23.1 kcal mole-' (Tb = 420°C).RESULTS The solubility data at 25°C is given in table 1 together with other thermodynamic data. The ideal solubility is calculated from the equation -AHi (T,-T) log xi = ~ -. 20303RT TT, M. VITORIA AND J . WALKLEY 59 Due to lack of information on the molal heat capacity of molten tetraphenyltin it was not possible to use the more accurate equation in which the temperature dependence of the heat of fusion is included. DISCUSSION For solutions of the dilution considered here the approximations 41 = 1 and 42 = x2V2/V1 (where x2 is the mole fraction of the solute) may be made. The solubility equation including the Flory-Huggins term can now be written Using the experimental data in table 1 the equation was solved to give the solute solubility parameter values also presented in this table.Excluding the values of d2 obtained from the first three solvents the average value for a2 is 10*6cal*cm-*. This is two units higher than the thermodynamic value of 8.5 obtained from the energy of vaporization AE" and its molar volume V The discrepancy between the (AEv/V2)* value and that from solubility measurements has been noted particularly for the molecule octamethylcyclotetrasiloxane,5 9 * a molecule similar to tetraphenyltin in having a bulky atom as a central core surrounded by relatively much smaller hydrocarbon groups. Thus a considerable part of the molal volume is contributed by this central core whereas the intermolecular force field arises almost entirely in the four peripheral hydrocarbon groups.S2 = (AE'/V2)' = [(AH'- RT)/V2]'. TABLE 1 .-SATURATION SOLUBILITY OF TETRAPHF~NYLTIN IN VARIOUS SOLVENTS key no. 1 2 3 4 5 6 7 8 9 10 11 12 -log x2 2.982 2.732 2.998 2-750 2.973 2.941 3.682 4.198 3-153 4.326 4.0035 4.068 V2l v1 5-154 4.914 3.980 3-533 3.241 2.938 2.884 2-620 2.556 1 494 1.066 1 a07 82 12.5 12.0 11.9 10.8 10-45 10.6 10.7 10-3 10.6 (9.6) 10.4 10.9 It is seen from table 1 that the regular solution self-consistent pattern of behaviour only exists up to a molar volume ratio of 3.5 1 even when Flory-Huggins terms are included. The noticeable disparity found for carbon disulphide dichloroethane and dichloromethane suggests an examination of the data in terms of a breakdown in the solvent-solute combining rules.The solubility equation may be written by replacing (6 - ~5,)~ by the term (dI2 + 622 - 2b6,6,) and by allowing b to become a numerical constant indicating the degree of deviation of a particular solute-solvent system from the geometric mean rule for which b = 1. In view of the difficulty in formulating the exact relationship between the cohesive energy density and the intermolecular potential 60 REGULAR SOLUTION THEORY between complex molecules it is reasonable to make a comparison with the combining rule for the pair-p~tential.~ This allows the cross-term to be written where CI1 and C2 are the cohesive energy densities of the pure solute and pure solvent. Il and I are the ionization potentials of the solvent and solute ol1 and 02 the collision diameters.The numerical constant b then becomes equal to the terms involving Z and Q. 12 oll and 022 are not known for the various molecules con- sidered here. In general differences in ionization potential are not large and the more serious error is likely to be due to difference in the diameters of the two molecules. With the approximation that oii3 is proportional to the molar volume and that 1 = 12 b reduces to b = (2)f VI v2 1‘ = K,. (VJ + if ( 1 8 - d1 I ) is obtained from the experimental data then b may be obtained from the identity (162-611)2 = 6f+6;-2bd16,. In table 2 values are presented for iodine stannic iodide and sulphur in a range of solvents using 61 = (AEv/Vl)* and the best average d2 value for the solute. b values for tetraphenyltin were determined in two ways ; first the rigorous thermodynamic value for a, 8.5 was used to give bT and secondly the average solubility value 10-6 gave bA.An overall agreement exists for the b values for all four solutes when the “ averaged ” solubility value of J2 is used. For tetraphenyltin any agreement between b, bT and K is merely fortuitous. The K values are far too small to be acceptable. TABLE 2.-b VALUES FOR VARIOUS SOLVENT-SOLUTE SYSTEMS solvent key no. I2 SnI4 S8 bA bT KO SnPh4 1 2 3 4 5 6 7 8 9 10 11 12 1 b o o 0 1.012 -973 - -980 -999 -995 1 403 - 1-003 1 *005 - -987 -995 - 1.008 1 -069 1 -053 - _. 1.019 -972 I -980 -952 ,982 -986 *997 1 *004 1 so03 1 -004 1 -000 I 998 - 1-01 1 1 -009 1-000 I 1 s o 4 5 1 -006 - *992 -976 -98 1 -984 -987 977 -986 -956 946 -983 *958 -959 ,854 -896 -900 *923 -93 6 * 944 -953 -954 *963 -964 a983 -999 1 *ooo When the above argument is reversed in order to predict a value for 6 from KO S and the experimental quantity ( I a2 -6 1 )2 a value for 6 exists only if the con- dition is satisfied.Even for carbon disulphide for which the most serious deviation from the averaged solubility 6 value is observed the lower bound for b is 0.971. If for these solute-solvent systems we solve for ( I d2 - J1 I ) 2 excluding the Flory-Huggins term in the solubility equation then the 4b26? -4[6:. -([I32 -s,1)2]2 2 0 Hence a lower bound for b is obtained. M. VITORIA A N D J . WALKLEY 61 deviation of b from unity is even more marked and no internally consistent value for a2 can be derived. The present paper shows that the regular solution solubility relationship extended by a Flory-Huggins term to accommodate a disparity in the molal volume of solvent and solute is surprisingly successful.Its break-down under the condition of extreme difference in V and V2 cannot be attributed to any breakdown in the geometric-mean rule used for the solute-solvent interaction parameter. Such consistency in 62 when the Flory-Huggins term is included in the solubility expression may be illusory. A factor contributing to the entropy term (e.g. +f(l- Y2/Vl)) can be balanced by the enthalpy term V24T(6 This can only be reflected in a study of the temperature dependence of the saturation solubility as has been made by Shinoda and Hildebrand O for solute-solvent systems of similar molar volume. ' J. H. Hildebrand J. Amer. Chem. Sue. 1929,51,66. G. Scatchard S. E. Wood and J. M. Mochel J . Amer. Chem. Suc. 1939,61,3206. E. B. Smith and J. Walkley Truns. Favaday SOC. 1960,56 1276. J. H. Hildebrand and R. L. Scott The Sulubifity of Nun-electrolytes. (Reinhold Publishing Corporation New York 1955) p. 135. J. E Jolley and J. H. Hildebrand J. Physic. Chem. 1957 61 791. G. G. Schlwinger Inorganic Laboratory Preparations. (Chemical Publishing Company Inc. New York 1962. H. Gilman and S. D. Rosenberg J . Arner. Chem. Soc. 1953 75 3593. J. H. Hildebrand and R. L. Scott Regular Solutions. (Prentice-Hall Inc. New Jersey 1962) pp. 123 and 146. G. H. Hudson and J. C. McCoubrey Trans. Faraday Soc. 1960,56,761. lo K. Shinoda and J. H. Hildebrand J. Physic. Chern. 1965 69,605.

ISSN:0014-7672    

DOI:10.1039/TF9696500057

出版商:RSC    

年代:1969

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions.Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Studies in Regular Solution Theory Part 2.-Entropy of Solution of Tetraphenyltin in Simple Non-polar Solvents BY M. VITORIA AND JOHN WALKLEY Dept. of Chemistry Simon Fraser University Burnaby 2 B.C. Canada f.?eceived 29th January 1968 The partial molal volume of tetraphenyltin in some non-polar organic solvents has been measured using a dilatometer method.The values obtained have been used to compare the entropy of solution at constant volume with that at constant pressure. Within the bounds of regular solution theory the usual Flory-Huggins term is inadequate. The formulation of an alternative which provides good agreement with the experimental data and the expected pattern of behaviour is discussed. The study of the behaviour of tetraphenyltin in non-polar organic solvents was undertaken to investigate regular solution behaviour for a solute-solvent system wherein a considerable disparity in molar volumes exists. In part 1 we considered the enthalpy of solution as revealed in the saturation solubility equation The symbols have their usual definiti0n.l The last term is the Flory-Huggins term which allows for the disparity between the molal volumes of the solvent and solute.The expression is written in terms of the 6 parameters (8 = (AEY/Vl)+) where AEv is the energy of vaporization and Yl is the molal volume of the liquid at 25"C and implies that a root-mean-square formulation is obeyed for the 1-2 interaction in solution. In part 1 a more rigorous form of the combining rule was examined but it was shown that the saturation solubility equation indicated a deviation from the simple geometric mean far too small to be interpreted in a more fundamental way. For tetraphenyltin the Flory-Huggins term was valid up to a molal volume ratio V2/ Y of 3. Beyond this specifically for carbon disulphide dichloromethane and dichloroethane no self-consistency in the solubility equation could be obtained.Hildebrand has shown that the entropy of solution which for a solid solute may be related to the temperature dependence of the solubility by log = log 4 2 + V24:(62 -6,)2/2.303 RT+0*434(1- VJVJ4;. with S. the entropy of the solid at 25"C is a more sensitive test of regular solution behaviour. The first term on the right-hand-side may be written 2v@ &)p,T = - V,x,RT x2' and for a solution of low solubility t h s term may be considered as unity. In this paper we examine the entropy of solution of tetraphenyltin in various solvents. By definition a regular solution is one involving " no entropy change when a small amount of one of its components if transferred to it from an ideal solution of the same composition the total volume remaining unchanged ."z For real solutions a finite volume change does occur on mixing.Measurements are reported here 62 63 for the partial molal volume of tetraphenyltin in the solvents considered allowing the entropy contribution from this volume change to be determined. The experi- mental partial molal volumes are compared to those obtained theoretically and the use of an " averaged " a2 value for the solute is shown to be apparently consistent within the present limitations of the theory. M. VITORIA AND J . WALKLEY EXPERIMENTAL The partial molal volume of tetraphenyltin in a number of solvents was measured using a dilatometer method. Two dilatometers having uniform capillaries of 2 mm int. diam. were used one being of 150 nil capacity the other of 10 ml to conserve solvent. A known '"Ot I2 I 1 I I 7 8 9 10 81 FIG.1 .-The partial mold volumes of tetrdphenyltin stannic iodide and iodine in various solvents are plotted against the solubility parameters of the solvents. weight of tetraphenyltin was added in a small glass capillary which was crushed under the solvent by a glass ball sealed into the dilatometer. The rise of the liquid level in the capillary was determined using a cathetometer. A correction was made for the-amount of glass added and the partial molal volume calculated from the expression V2 = zr2A2M,/w2 where Y is the radius of the capillary A2 the corrected rise in the liquid level w2 is the weight of the solute and Mz is its molecular weight. Three successive determinations were made for each solvent. The dilatometers were immersed in a water-bath held constant at 25°C by a large toluene regulator.No temperature fluctuations of the liquid level were observed. The scatter of results indicated an error of 0-8 %. In fig. 1 the variation of the partial molal volume of tetraphenyltin is plotted against the solubility parameter of the solvent. Data for stannic iodide and iodine are included for comparison ; the same trend is evident for all three solutes. The temperature dependence of the saturation solubility is determined from the saturation solubility results presented in part 1. 64 REGULAR SOLUTION THEORY DISCUSSION The temperature dependence of the saturation solubility can be derived from the saturation solubility expression and is given by = R In x i -(R In x2 +Q) where Q = R[ln (V,/ V,) + (1 - V2/ V,)]. For a solute-solvent system of comparable mold volumes Q tends to zero.FIG. 2 . T h e entropy of solution of tetraphenylth at constant pressure plotted against - (R In x2 + Q). Numbers refer to solvents as given in table 1. In fig. 2 we present a plot of ( S - p2)p against -(R In x2 + Q) using the data of table 2. The deviation from the regular solution line of unit slope and intercept R In xi is typical and may be regarded as due to the contribution from the entropy of volume expansion. This may be written where v2 and Vz are the partial molal volume and the hypothetical reference volume of the solute and (aP/dT) is the isochore of the pure solvent. The volume expansion on solution may be calculated from an expression of Hildebrand where yt is the ratio [(aE/i3V),/(E/V),,,] for the pure solvent is its compressibility and y2 the activity coefficient of the solute.When the Hildebrand solubility equation is applied viz. v2 - V ; = nPRV In y2 In y2 = In (a2/x2) = v,o&(S - 6 1 2 / ~ ~ , M. VITORIA AND J . WALKLEY 65 For the systems considered here a Flory-Huggins term is required in the saturation solubility equation and this requires In y2 to be redeked as and hence TABLE 1 .-THEORETICAL AND EXPERIrnNTAL PARTIAL MOLAL VOLUMES (25°C) solvent 61 12.5 11-9 10.8 10.6 10-7 10.6 9-6 10-4 10.9 V2 (calc.) - eqn. (1) h a ) h 8 ) 2-8 9 4 - 1.6 2.6 1.0 1-8 1.7 1-7 - 0.2 0.6 0-6 0-6 -2.5 -18.2 -0-2 -1.2 1.6 4.4 V2 (expt.1 eqn. (2) az(a) %S) - 2.4 4.1 - 4-7 0.2 - 2.3 - 1.5 - 0.3 - 0.3 - 2.8 - 2-0 - 0.7 - 0.7 -3.6 -19.4 - 0.3 - 0.7 1 *6 4.4 TABLE TH THE ENTROPY OF SOLUTION AT (a) CONSTANT PRESSURE AND (b) CONSTANT VOLUME 1 2 3 4 5 6 7 8 9 10 11 12 solvent -Rlnxz - 13.597 12.458 13.671 12.540 13.557 13.41 1 16.790 19.143 14-377 19.726 18.256 18-550 (a In xzf Q) 18.575 17,055 16.835 15*055 15.666 15.113 18.422 20.444 15.600 20.232 1 8.263 18.550 AS! A v(aP/aT) v 33.07 - '727 23.36 - 199" 26.34 -767 24-04 *569 27.36 .590* 16-48 ,533 32.87 3.539 36.47 3 -204* 27.12 -857 29.05 6.724 35-12 AS? 33.79 23-16 25.57 23 *47 26.77 15-93 30.33 33.27 26.26 22-33 *calculated from eqn.(2) using the 82(s) value. The hypothetical molal volume Vg of liquid tetraphenyltin (extrapolated from the melting point to 25°C) was determined ; if the numerical value of a2 can be established then a theoretical v2 can be found. Theoretical values are quoted using eqn. (1) and (2) and for a d2 value determined directly from the saturation relationships (called S,,,,) and from the '' averaged " value 62(a).In table 1 the individual i5z(s) values are considerably different from the averaged value = 10-6) particularly for a small solvent niolal volume. In table 1 we give the experimentally measured partial molal volume and the difference terms v2 (calc.) - r2 (expt.). Eqn. (2) fails to give any overall improvement over eqn. (1) even when 6z(s) is used. However in order to avoid predicting a partial molal volume less than the hypothetical molal volume of tetraphenyltin at 25°C (314 cm3 mole-') we must use 62(s) if we include the Flory-Huggins terms (e.g. for CHzClz solvent v2 = 309.2 ; v2 (a2(*)) = 3151). 3 66 REGULAR SOLUTION THEORY Using the experimental V2 values (or those obtained from eqn.(2) using 62(sJ the entropy of solution at constant volume may be found using the entropy of volume expansion. This value ASv is plotted against -(R In x2 + Q) in fig. 3 but no conformity is found with the regular solution line. Shinoda and Hildebrand have discussed some irregular solutions of iodine and have tried to determine whether the departure from the regular solution entropy line is due to entropy or enthalpy effect. Thus iodine+solvent systems which depart from a log x2 against (6 - 62)2 plot using the iodine a2<,> value of 14.1 but which are I 0 0 10 20 -(R In xzi- Q) FIG. 3.-The entropy of solution of tetraphenyltin at constant volume plotted against - (R In x2 -t- Q). Numbers refer to solvents as given in table 2. '' regular " for a ASv against - R In x2 plot suggest that a " physical " factor which might cause the entropy to depart from the ideal is offset by a corresponding change in the enthalpy.The entropy plot does not involve the solubility parameters. For the tetraphenyltin solutions the " Flory-Huggins " term is large and this essentially entropy term can simply be balanced by the V,+f (6 - 6J2/RT enthalpy term. The necessity of the inclusion of this term in both the solubility and entropy expression precludes an analysis of the present system by the Hildebrand method. Regular solution behaviour requires a solute to be characterized by a consistent d2 value and this is true for a wide range of solutes.' With 6 = 10-6 for tetra- phenyltin in agreement with the values obtained from solution in solvents of molal volume similar to the solute we use the saturation solubility equation to determine a term Av apparently contributed because of the solvent-solute molal volume disparity viz.Av = log X - log42 - V24:(62 - 6,)2/RT. M. VITORIA AND J. WALKLEY 67 In eqn. (1) Av has the Flory-Huggins formulation (i.e. 0.43 (1 - V2/V&:). The values so obtained are given in table 3 and a graphical comparison is made with values predicted by the Flory-Huggins equation in fig. 4. The erratic pattern of behaviour reflects the sensitivity to the (6,-~5,)~ term. With a2 = 10.4 then for carbon disulphide Av = -0.42 rather than -0.46 and for carbon tetrachloride -0.94 rather than - 1.1 with a2 = 10.6. The relative scatter remains and it is not rewarding to attempt to find some smooth relationship by a series of small adjustments to a1 and d2.However irrespective of the value chosen for J2 the Av term for tetraphenyltin in the solvents of small molal volume always decreases well below the Flory-Huggins line and is always less than that for those solvents in which V2/V V2l Vl to solvents as given in table 2. FIG. 4-The volume disparity term Av plotted against the volume ratio V2/Yl. Numbers refer is about 2. Having established the Av term we may redetermine the -R(ln x2 + Q) term expressing Q as Qv where Qv = +R(ln ( V2/V1) + 2.303 Av). The A S P against (R In x2+ Qv) plot is given in fig. 5 and the ASy against - (R In x2 + Qv) plot is given in fig. 5 and the ASv against - (R In x2 + QV plot in fig. 6. In constructing the latter from the former the inclusion of the entropy of expansion term gives an overall pattern conforming with regular solution behaviour.The line of unit slope and of intercept R In xi is well defined. It is of little value to repeat the calculations for different values of a2 until the intercept is exactly the figure expected i.e. 12.13. Finally use is made of the Av term in the prediction of the theoretical partial molal volume against using the value of 10-6 for all systems. The equation now is v2 - V i = nPRT[ln (Y;/V1) +23034;A,+ Vi4i(S2-al)2/RT]. 68 REGULAR SOLUTION THEORY - - - - 6 3 0 - - 10 I - 2 - w r i -(R x2+ Qv) FIG. 5.-The entropy of solution of tetraphenyltin at constant pressure plotted against -(Rlnx2 + Qv). Numbers refer to solvents as given in table 2. -(R In x2+ Qv> FIG. 6.-The entropy of solution of tetraphenyltin at constant volume plotted against - (Rln x2 + Q v).Numbers refer to solvents as given in table 2. M. VITORIA AND J. WALKLEY 69 A comparison of this value with experimental data is given in table 3 and it is as successful as the combination of eqn. (2) and the 82(s) values. The theoretical V2 value is however sensitive to a2 and within the limitation of these calculations the prediction of v2 is good. TABLE 3.-AN ALTERNATIVE FLORY-HUGGMS TERM AND RELATED QUANTITIES 1 2 3 4 5 6 7 8 9 10 11 12 solvent A y -( - 4-62 - -756 - -398 - .934 -1.112 - -845 - *759 - 1 -092 - -653 - 1.852 - -236 + -297 R In xz+ Q v) 12.465 12.765 12.757 14.31 1 16.316 15-140 18.165 22.230 15-507 26.935 18-096 17-179 V 3 15.99 3 14-90 3 16.06 3 15-00 3 16-53 3 1 6-00 322-00 329.92 3 17.00 331-96 320.31 326-82 % apt.3 12.00 3 16-68 3 16.32 3 16-32 324-42 3 17.60 350.91 321.48 322.62 - - - Only the solutions of tetraphenyltin in carbon disulphide and toluene depart widely from regular solution behaviour. For each the deviation is nearly 10 cal/mole deg. but of opposite sign. A simple molal volume disparity argument will not account for this because for both dichloromethane and dichloroethane with VJV ratios of 4.9 and 4.0 a reasonable agreement with the expected pattern of behaviour is obtained. The deviations found with these solvents remain undeter- mined. N. Vitoria and J. Walkley Trans. Furaday SOC. 1969 65 57. J. H. Hildebrand and R L. Scott Regular Solutions (Prentice-Hall Inc. New Jersey 1962) p. 4. E. B. Smith and J. Walkley Trans. Faruduy Soc. 1960,56 1276. ref. (2) p. 108. K. Shinoda and J. H. Hildebrand J . Physic. Chern. 1965,69,605. G. Scatchard Trans. Fmaday SOC. 1937,33 160. New York 1964). ’ J. H. Hildebrand and R. L. Scott The SolubiZity of Nonelectrolytes (Dover Publications Inc.,

ISSN:0014-7672    

DOI:10.1039/TF9696500062

出版商:RSC    

年代:1969

数据来源: RSC