Pub Date : 1976-05-01DOI: 10.1016/0001-8716(76)80016-8
Friedrich Kohler, Pierre Huyskens
The different aspects which are considered here are the influence of the medium on the formation of hydrogen bonds, the cyclization of aggregates, the polarity of the bonds and the ionization processes, and the influence of the first hydrogen bond on the formation of a second one. The stability of the complexes is influenced by the non-specific and specific interactions between the complex and the separated constituents, respectively, and the molecules of the surrounding medium. When the solvent molecules exhibit specific sites which can compete with those of the donor or of the acceptor, the complexation is reduced. This is also the case, when the solvent molecules are highly polarizable. On the other hand, when polar species are present in the medium, interaction parameters between these species and the polarizable complexes must be taken into account. This is particularly the case for the interaction between the complex triethylamine-acetic acid and the dimer of this acid.
Cyclization can only occur to an appreciable extent for low aggregates because the cyclization of higher aggregates is completely disfavoured by the loss of entropy which is not compensated for by the energy of the additional bond. Thus whilst dimers of the higher carboxylic acids are mostly in the cyclic form, and whilst the lower aggregates (trimers, tetramers …) of the alcohols and of the phenols show an appreciable cyclization, the higher aggregates of the latter substances predominantly assume non-cyclic forms. Sometimes, as a necessary prerequisite, cyclization requires a specific conformation of the monomer. This possibly explains why the cyclization is less effective in formic acid where the “trans” isomer is more important, and is almost completely absent in propionamide, where the cis-form is practically nonexistent.
In many cases there exist two energy levels of potential energy for the proton participating in a hydrogen bond. The equilibrium constant Ki between the two protomers depends (for a given family of complexes and in a given medium) on the difference between the pKBH+ of the base and the pKHA of the acid. Below a certain range of ΔpK the normal bond entirely predominates, whereas the reverse is true above this range. The predominancy of a given form can be shown by various methods such as NMR spectrometry, measurements of dipole moments, solubility, etc. Solvation of the complex by molecules of the medium can influence the energy of the two protomers and thus Ki.
When a molecule has an H-bond as proton donor, the tendency of other sites of this molecule to act as proton donor decreases, whereas their tendency to act as electron-donor sites is enhanced. The reverse is true for molecules acting as electron donors. These effects are particularly strong if the hydrogen bond formed involves a (partial) proton transfer
{"title":"Some aspects of the structure and interaction potential of hydrogen bonded complexes","authors":"Friedrich Kohler, Pierre Huyskens","doi":"10.1016/0001-8716(76)80016-8","DOIUrl":"10.1016/0001-8716(76)80016-8","url":null,"abstract":"<div><p>The different aspects which are considered here are the influence of the medium on the formation of hydrogen bonds, the cyclization of aggregates, the polarity of the bonds and the ionization processes, and the influence of the first hydrogen bond on the formation of a second one. The stability of the complexes is influenced by the non-specific and specific interactions between the complex and the separated constituents, respectively, and the molecules of the surrounding medium. When the solvent molecules exhibit specific sites which can compete with those of the donor or of the acceptor, the complexation is reduced. This is also the case, when the solvent molecules are highly polarizable. On the other hand, when polar species are present in the medium, interaction parameters between these species and the polarizable complexes must be taken into account. This is particularly the case for the interaction between the complex triethylamine-acetic acid and the dimer of this acid.</p><p>Cyclization can only occur to an appreciable extent for low aggregates because the cyclization of higher aggregates is completely disfavoured by the loss of entropy which is not compensated for by the energy of the additional bond. Thus whilst dimers of the higher carboxylic acids are mostly in the cyclic form, and whilst the lower aggregates (trimers, tetramers …) of the alcohols and of the phenols show an appreciable cyclization, the higher aggregates of the latter substances predominantly assume non-cyclic forms. Sometimes, as a necessary prerequisite, cyclization requires a specific conformation of the monomer. This possibly explains why the cyclization is less effective in formic acid where the “<em>trans</em>” isomer is more important, and is almost completely absent in propionamide, where the <em>cis</em>-form is practically nonexistent.</p><p>In many cases there exist two energy levels of potential energy for the proton participating in a hydrogen bond. The equilibrium constant <em>K</em><sub>i</sub> between the two protomers depends (for a given family of complexes and in a given medium) on the difference between the p<em>K</em><sub>BH<sup>+</sup></sub> of the base and the p<em>K</em><sub>HA</sub> of the acid. Below a certain range of Δp<em>K</em> the normal bond entirely predominates, whereas the reverse is true above this range. The predominancy of a given form can be shown by various methods such as NMR spectrometry, measurements of dipole moments, solubility, etc. Solvation of the complex by molecules of the medium can influence the energy of the two protomers and thus <em>K</em><sub>i</sub>.</p><p>When a molecule has an H-bond as proton donor, the tendency of other sites of this molecule to act as proton donor decreases, whereas their tendency to act as electron-donor sites is enhanced. The reverse is true for molecules acting as electron donors. These effects are particularly strong if the hydrogen bond formed involves a (partial) proton transfer","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 2","pages":"Pages 125-154"},"PeriodicalIF":0.0,"publicationDate":"1976-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80016-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79055505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-05-01DOI: 10.1016/0001-8716(76)80015-6
Joanna Sadlej
The localized molecular orbitals for the hydration complexes of H+ and Li+ cations, F− anion, and linear dimer of water molecules are obtained from their CNDO/2 wavefunctions. The bonding of these systems is qualitatively discussed in the light of the localized orbitals.
{"title":"Semiempirical calculation of electronic redistributions in interacting molecular systems III. Localized charge distributions 1n the hydration complexes of cations and anions","authors":"Joanna Sadlej","doi":"10.1016/0001-8716(76)80015-6","DOIUrl":"10.1016/0001-8716(76)80015-6","url":null,"abstract":"<div><p>The localized molecular orbitals for the hydration complexes of H<sup>+</sup> and Li<sup>+</sup> cations, F<sup>−</sup> anion, and linear dimer of water molecules are obtained from their CNDO/2 wavefunctions. The bonding of these systems is qualitatively discussed in the light of the localized orbitals.</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 2","pages":"Pages 117-123"},"PeriodicalIF":0.0,"publicationDate":"1976-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80015-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84478249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-05-01DOI: 10.1016/0001-8716(76)80012-0
P.J. Heywood, J.E. Rassing, Evan Wyn-Jones
{"title":"Ultrasonic relaxation studies of proton transfer in poly-l-lysine","authors":"P.J. Heywood, J.E. Rassing, Evan Wyn-Jones","doi":"10.1016/0001-8716(76)80012-0","DOIUrl":"10.1016/0001-8716(76)80012-0","url":null,"abstract":"","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 2","pages":"Pages 95-101"},"PeriodicalIF":0.0,"publicationDate":"1976-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80012-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84128393","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-05-01DOI: 10.1016/0001-8716(76)80014-4
J. Crossley, S.C. Srivastava
Dielectric constants and losses have been measured at eight microwave frequencies between 1 and 35 GHz for 1-butanol and 1-decanol in paraffin oil and paraffin oil-n-heptane mixtures at 25 °C. The data have been analyzed in terms of two relaxation times and their dependence on viscosity and concentration is examined. The dielectric relaxation behaviour of these alcohols is not affected to any appreciable extent by increased macroscopic viscosity.
{"title":"Macroscopic viscosity and the dielectric relaxation of 1-butanol and 1-decanol","authors":"J. Crossley, S.C. Srivastava","doi":"10.1016/0001-8716(76)80014-4","DOIUrl":"10.1016/0001-8716(76)80014-4","url":null,"abstract":"<div><p>Dielectric constants and losses have been measured at eight microwave frequencies between 1 and 35 GHz for 1-butanol and 1-decanol in paraffin oil and paraffin oil-<em>n</em>-heptane mixtures at 25 °C. The data have been analyzed in terms of two relaxation times and their dependence on viscosity and concentration is examined. The dielectric relaxation behaviour of these alcohols is not affected to any appreciable extent by increased macroscopic viscosity.</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 2","pages":"Pages 111-116"},"PeriodicalIF":0.0,"publicationDate":"1976-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80014-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77071649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-05-01DOI: 10.1016/0001-8716(76)80013-2
A.R. Foweraker, B.R. Jennings
The decay of the transient birefringence induced by pulsed electric fields has been recorded and analysed for two different aqueous, polydisperse systems of rod-shaped particles. Attapulgite needles and asbestos fibres were the materials studied. The initial slopes of graphs of the logarithm of the normalised amplitudes during the decay process as a function of time were evaluated for both low and high electric field strengths. By comparing the data with those obtained from a simultaneous electron microscopic study, we verify the predictions of earlier theory from this research group that (i) discrete polydispersity average parameters are obtained from the initial slopes, (ii) from two such averages, which are quickly measured by this method, the sample polydispersity is indicated and (iii) the “peeling” method commonly used hitherto can give misleading size parameters.
{"title":"Electro-optic decay analysis for polydisperse systems III. Experimental data for rods","authors":"A.R. Foweraker, B.R. Jennings","doi":"10.1016/0001-8716(76)80013-2","DOIUrl":"10.1016/0001-8716(76)80013-2","url":null,"abstract":"<div><p>The decay of the transient birefringence induced by pulsed electric fields has been recorded and analysed for two different aqueous, polydisperse systems of rod-shaped particles. Attapulgite needles and asbestos fibres were the materials studied. The initial slopes of graphs of the logarithm of the normalised amplitudes during the decay process as a function of time were evaluated for both low and high electric field strengths. By comparing the data with those obtained from a simultaneous electron microscopic study, we verify the predictions of earlier theory from this research group that (i) discrete polydispersity average parameters are obtained from the initial slopes, (ii) from two such averages, which are quickly measured by this method, the sample polydispersity is indicated and (iii) the “peeling” method commonly used hitherto can give misleading size parameters.</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 2","pages":"Pages 103-110"},"PeriodicalIF":0.0,"publicationDate":"1976-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80013-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73262297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-05-01DOI: 10.1016/0001-8716(76)80017-X
O.J. Heilmann
The explicit expression for the relaxation spectrum of the polymerization reaction A1 + An ⇌ An+1 (n 1, 2, …) where all reactions are supposed to have the same values of the thermodynamic and kinetic parameters, is given. The result deviates significantly from what would be predicted if the reactions were considered to be independent.
{"title":"Explicit expression for the relaxation spectrum of a model with infinitely many coupled chemical reactions","authors":"O.J. Heilmann","doi":"10.1016/0001-8716(76)80017-X","DOIUrl":"10.1016/0001-8716(76)80017-X","url":null,"abstract":"<div><p>The explicit expression for the relaxation spectrum of the polymerization reaction <em>A</em><sub>1</sub> + <em>A<sub>n</sub></em> ⇌ <em>A</em><sub><em>n</em>+1</sub> (<em>n</em> 1, 2, …) where all reactions are supposed to have the same values of the thermodynamic and kinetic parameters, is given. The result deviates significantly from what would be predicted if the reactions were considered to be independent.</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 2","pages":"Pages 155-168"},"PeriodicalIF":0.0,"publicationDate":"1976-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80017-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72931619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-03-01DOI: 10.1016/0001-8716(76)80003-X
R.K. Harris, B.J. Kimber
Silicon-29 spin-lattice relaxation times and 29Si{1H} nuclear Overhauser enhancements are reported for five trialkylsilanes and fo sym-tetramethyldisiloxane, all of which contain a direct SiH bond. Relaxation rate contributions from (Si, H) dipolar interactions and fro other mechanisms are evaluated and discussed in terms of molecular mobility. For the smaller molecules it is concluded that the spin-rotation contribution to (T1)-1 is dominant but, when the alkyl groups are bigger than ethyl, dipolar interactions are more important than spin-rotation. Silicon-29 chemical shifts and coupling constants are also presented and briefly discussed.
{"title":"29Si and 13C Nuclear magnetic resonance studies of organosilicon chemistry","authors":"R.K. Harris, B.J. Kimber","doi":"10.1016/0001-8716(76)80003-X","DOIUrl":"10.1016/0001-8716(76)80003-X","url":null,"abstract":"<div><p>Silicon-29 spin-lattice relaxation times and <sup>29</sup>Si{<sub>1</sub>H} nuclear Overhauser enhancements are reported for five trialkylsilanes and fo <em>sym</em>-tetramethyldisiloxane, all of which contain a direct SiH bond. Relaxation rate contributions from (Si, H) dipolar interactions and fro other mechanisms are evaluated and discussed in terms of molecular mobility. For the smaller molecules it is concluded that the spin-rotation contribution to (<em>T</em><sub>1</sub>)<sup>-1</sup> is dominant but, when the alkyl groups are bigger than ethyl, dipolar interactions are more important than spin-rotation. Silicon-29 chemical shifts and coupling constants are also presented and briefly discussed.</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 1","pages":"Pages 15-22"},"PeriodicalIF":0.0,"publicationDate":"1976-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80003-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81535873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-03-01DOI: 10.1016/0001-8716(76)80010-7
K. Lundy-Douglas, Z.A. Schelly
The relaxation mechanism of electronically excited 8-hydroxypyrene-1,3,6-trisulfonic acid (HPT) and 6,8-dihydroxypyrene-1,3-disulfonic acid (DPD) has been studied using flash perturbation method in aqueous solution. The recombination rate constants kr of the solvated electron (ejected from the excited state of the dissociated acids) have been determined. No electron ejection takes place in aqueous 8-aminopyrene-1,3,6-trisulfonic acid (APT).
{"title":"Relaxation study of excited aqueous hydroxypyrenes","authors":"K. Lundy-Douglas, Z.A. Schelly","doi":"10.1016/0001-8716(76)80010-7","DOIUrl":"10.1016/0001-8716(76)80010-7","url":null,"abstract":"<div><p>The relaxation mechanism of electronically excited 8-hydroxypyrene-1,3,6-trisulfonic acid (HPT) and 6,8-dihydroxypyrene-1,3-disulfonic acid (DPD) has been studied using flash perturbation method in aqueous solution. The recombination rate constants <em>k</em><sub>r</sub> of the solvated electron (ejected from the excited state of the dissociated acids) have been determined. No electron ejection takes place in aqueous 8-aminopyrene-1,3,6-trisulfonic acid (APT).</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 1","pages":"Pages 79-86"},"PeriodicalIF":0.0,"publicationDate":"1976-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80010-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88246079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1976-03-01DOI: 10.1016/0001-8716(76)80004-1
R.K. Harris, B.J. Kimber
29Si and 13C spin-lattice relaxation times and the corresponding nuclear Overhauser enhancements have been measured for PhnSiH4−n (n = 1, 2, 3), for Ph2SiHMe and for Ph2SiCl2. Thence dipolar and other contributions to the relaxation rates have been separated. The dipolar rates are used to discuss internal rotation about the phenyl-Si bond, and overall motional anisotropy. The value of T1(Si) for PhSiH3 is very short and, it is suggested, is dominated by the spin-internal-rotation interaction. Values of chemical shifts and coupling constants are also presented and briefly discussed.
{"title":"29Si and 13C Nuclear magnetic resonance studies of organosilicon chemistry","authors":"R.K. Harris, B.J. Kimber","doi":"10.1016/0001-8716(76)80004-1","DOIUrl":"10.1016/0001-8716(76)80004-1","url":null,"abstract":"<div><p><sup>29</sup>Si and <sup>13</sup>C spin-lattice relaxation times and the corresponding nuclear Overhauser enhancements have been measured for Ph<em><sub>n</sub></em>SiH<sub>4−n</sub> (<em>n</em> = 1, 2, 3), for Ph<sub>2</sub>SiHMe and for Ph<sub>2</sub>SiCl<sub>2</sub>. Thence dipolar and other contributions to the relaxation rates have been separated. The dipolar rates are used to discuss internal rotation about the phenyl-Si bond, and overall motional anisotropy. The value of <em>T</em><sub>1</sub>(Si) for PhSiH<sub>3</sub> is very short and, it is suggested, is dominated by the spin-internal-rotation interaction. Values of chemical shifts and coupling constants are also presented and briefly discussed.</p></div>","PeriodicalId":100050,"journal":{"name":"Advances in Molecular Relaxation Processes","volume":"8 1","pages":"Pages 23-35"},"PeriodicalIF":0.0,"publicationDate":"1976-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-8716(76)80004-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87354257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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