ISSN:0005-9021    

DOI:10.1002/bbpc.197800084

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractDepolarized Rayleigh scattering experiments on neat acetonitrile and carbon disulfide as well as on mixtures of these liquids with carbon tetrachloride are reported. The collective reorientational correlation time τLShas been determined which is then compared with the single particle correlation time τS. From the comparison information on an orientational structure factorg(2), which is closely related to the Kirkwoodg‐factor of polar fluids, can be obtained. Combination ofg(2)and Kirkwoodg‐factor results shows that a preferred antiparallel alignment is the most probable orientational structure in acetonitrile. For CS2a Kirkwoodg‐factor cannot be defined due to symmetry. Here the experiments indicate a preferred parallel arrangement of neighbouring mo

ISSN:0005-9021    

DOI:10.1002/bbpc.197800085

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractMit Hilfe der1H‐Kernresonanzspektroskopie wird das Mischassoziationsverhalten schwacher Lewissäuren (mehrfach‐chlorsubstituierte Benzole) mit organischen Basen (HMPT) untersucht. Die im Frequenzsweep‐Verfahren gemessene Abhängigkeit der Lösungsmittelverschiebung von der Basenkonzentration wird nach dem Kontaktmodell [18] ausgewertet. Die einer schwachen H‐Brücke entsprechenden Wechselwirkungsenergien (‐9,6 bis −16,8 kJ/mol) zwischen den Aromatenprotonen und der Base zeigen Additivität in Beiträgen von 0‐, m‐ und p‐Chloratomen. Das additive Verhalten substituentenstellungsspezifischer Wechselwirkungsinkremente wird durch thermodynamische Messungen bei den Di

ISSN:0005-9021    

DOI:10.1002/bbpc.197800086

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractProton spin‐lattice and spin‐spin relaxation times of DMSO solutions with Mn(ClO4)2between 298 K ⩽T⩽ 413 K have been measured over a relatively wide frequency range (10 kHz ⩽v⩽ 90 MHz). Three regions exist where the relaxation times of solvent DMSO are frequency dependent. It is possible to extract from these experimental data structural and dynamical parameters such as the number of complexed DMSO molecules, their mean lifetime in the first solvation sphere around the metal ions, and/or the rotational diffusion constant of the [Mn(DMSO)6]2+complex. These data are necessary for a better understanding of the EPR relaxation mechanism of manganese ions in the same environment, where considerable line broadening at higher temperatures (T⩾ 373 K) has

ISSN:0005-9021    

DOI:10.1002/bbpc.197800087

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractUsing pulse radiolysis with conductivity detection and steady state γ‐radiolysis it is shown that in aqueous solution the reaction of OH radicals with 2,3‐ and 4‐monohalo (X = F, Cl, Br) anisoles leads to the production of hydrogen halides (HX). The G‐values for production of hydrogen halides measured 10 μs after the pulse are large for the 2‐ and 4‐haloanisoles (G(HX) = 0.5‐1.45) and small for the 3‐haloanisoles (G(HX) = 0.1‐0.3). These yields reflect the amount of OH addition to ring positions substituted by X. The differences in these amounts reflect an ortho‐para directing activity of the methoxy group. – In the case of the OH adducts of 3‐haloanisoles – in contrast to those of 2‐ and 4‐haloanisoles – in addition to the prompt a second order elimination of HX is observed which occurs on the ms time‐scale. This shows that the distribution of OH addition cannot always be obtained from product studies using γ‐radiolysis. TheG(HX) values measured using steady state γ‐radiolysis agree with those determin

ISSN:0005-9021    

DOI:10.1002/bbpc.197800088

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractAg+2radical cations were produced in aqueous 1 · 10−4molar Ag2SO4solutions containing micelles of sodium hexadecyl trioxiethylene sulfate and of sodium dodecylsulfate by a short pulse of high energy electrons. The disappearance of Ag+2and the appearance of Ag2were followed by optical measurements in the 10−6to 10−2s range. – A fraction of the Ag+2radicals decayed within 1 to 2 microseconds, and the remaining radicals disappeared in a second order process within 10−4to 10−2s. These decay processes are attributed to(a) intramicellar or two‐dimensional radical‐radical reaction at the surface of doubly occupied micelles, and(b) intramicellar or three‐dimensional reaction between radicals that are singly adsorbed at micelles. The fraction of (a) increases with increasing concentration ratio of radicals to micelles as expected from statistical considerations. Deviations at low concentration ratios are attributed to the initial formation of some of the radicals in spurs. The observed 100 fold acceleration of the radical‐radical reaction by the reduction in the dimensionality of reaction space is also compared to similar effects in fast biochemical reactions on large carrier molecules.It is concluded from an analysis of the dependence of the bimolecular rate constant of reaction (b) on the tenside concentration that Ag+2cations reside longer than milliseconds at micelles and can be exchanged directly between two anionic micelles. The rate constants are given

ISSN:0005-9021    

DOI:10.1002/bbpc.197800089

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractElectron exchange between the conduction band of an oxide electrode and a redox electrolyte in the presence of a space charge barrier is investigated. Two electron transfer mechanisms through the barrier are studied in detail: direct elastic tunnelling and resonance tunnelling via localized states in the band gap. Current/overpotential characteristics are calculated for both mechanisms in dependence on various system parameters such as the Debye length and the band bending. Though the characteristics have a number of features in common, some criteria can be established to distinguish between the two types of tunnelling. The theoretical results are compared with data from several experimental studies; there is evidence that both tunnelling mechanisms occur in real systems.

ISSN:0005-9021    

DOI:10.1002/bbpc.197800090

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractInvestigations of the anodic oxidation of ethylene glycol at gold in alkaline solutions by cyclic voltammetry at stationary as well as rotating ring‐disc electrodes and by controlled potential electrolysis combined with chemical and mass spectroscopic analysis yield the following results:1) Within the overall reaction 8 electrons per EG‐molecule are transferred the final product beeing oxalate. Glycol‐aldehyde, glycolate, glyoxal, and glyoxalate have been identified as intermediates or by products.2) The kinetics of the process is determined by a 1‐electron step, the transfer coefficient amounts α = 0.34. The anodic reaction orders are ZEG= 1 and ZOH‐ = 0, rsp.These results are interpreted by means of a reaction mechanism. The process is assumed to be catalyzed by a gold oxide surfa

ISSN:0005-9021    

DOI:10.1002/bbpc.197800091

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractThe formation of the inner‐sphere complex of BeSO4in mixtures of water and formamide has been investigated using the pressure‐jump relaxation method. Whereas in the two pure solvents the reaction is characterized by a single relaxation time in the solvent mixtures two relaxation processes superimpose and which are attributed to the replacement of a water or a formamide molecule, respectively, in the inner‐sphere by the entering sulphate ion. – The multistep association mechanism proposed by Eigen and Tamm [1] prevails also in the solvent mixtures. With increasing mole fraction of formamide the dielectric constant increases and in accordance with Fuoss equation [2]the association constants of the outer‐sphere complexes decrease. However, the inner‐sphere stability constants increase sharply so that the total association constants of BeSO4. increase with the formamide content. The ligand assisted dissociative process (Id[3]) outer‐sphere r̊ inner‐sphere complex is discussed in terms of a concerted mechanism proposed earlier for aqueo

ISSN:0005-9021    

DOI:10.1002/bbpc.197800092

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY

摘要:

AbstractProton magnetic resonance spectra of Be(NO3)2solutions in mixtures of water and dimethylsulphoxide (DMSO) have been measured at different solvent compositions and temperatures at 270 MHz. The relative amounts of the solvated species Be(OH2)i(DMSO)4−ihave been determined. The total solvation number was 4. The kinetics of solvent exchange has been studied in DMSO. The proton exchange in pure aqueous solutions may be explained in terms of a protolysis reaction. The solvent molecule preferentially solvating the beryllium ion is DMSO in water rich solutions and water in DMSO rich solution

ISSN:0005-9021    

DOI:10.1002/bbpc.197800093

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1978

数据来源: WILEY