Dielectric studies. Part XIX. Molecular relaxation of some rigid molecules

Crossley, J.; Hassell, W. F.; Walker, S.

doi:10.1139/v68-355

Cited by 13 publications

(8 citation statements)

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“…However, results of Crossley and Walker (1968) for quinoline in cyclohexane at 50°C, in p-xylene at 25 and 50°C, and for isoquinoline in cyclohexane and p-xylene at 25 and 50°C confirm a similar pattern for a as that found for pyridine. This is expected of rigid polar molecules which obviously lack flexible dipole elements and, --.., therefore, ~o n f o u n to the simple Debye relaxation pattern.…”

Section: Resultssupporting

confidence: 73%

“…The value of 4.4 ps at 13°C reported by Chau et al (1957) is consistent with these values but the relaxation time of 4.6 ps given by Crossley et al (1968) at 25°C is longer and is in conflict with these measurements. For quinoline and isoquinoline molecules in benzene, relatively few literature values are available for comparison.…”

Section: Resultssupporting

confidence: 67%

“…The Cole-Cole plots of Crossley et al (1968) for pyridine in benzene, p-xylene, and carbon tetrachloride at 25°C and in cyclohexane at 25 and 50°C also gave a zero or a small value for a. They ascribe the non-zero values to a distribution of relaxation times about a mean value.…”

Section: Resultsmentioning

confidence: 95%

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Microwave absorption and dielectric relaxation of some rigid molecules and their mixtures

Madan¹,

Shelfoon²,

Cameron³

1977

Can. J. Phys.

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The dielectric constant and loss factor of some rigid molecules. pyridine, quinoline, and isoquinoline, and their mixtures have been measured in dilute benzene solutions in the microwave region over a range of temperatures. The dielectric data have been used to determine the relaxation times and the thermodynamic parameters for the activated state. The values of the relaxation time for single polar component solutions agree well at temperatures at which there are available known data. The relaxation times for the mixtures are consistent with the results on simple liquid mixtures of polar molecules in dilute solutions which were previously studied by us and by some other workers. On a mesure la constante dielectrique et le facteur de perte de quelques mol6cules rigides, pyridine, quinoline et isoquinoline, et de leurs melanges en solution diluee dans le benzene, dans la region des micro-ondes et pour un intervalle de temperatures. A partir de ces donnees dielectliques, on a determine les temps de relaxation et les parametres thermodynamiques de I'etat active. Les valeursdu temps de relaxation pour les solutions a une seule composante polaire sont en bon accord avec les donnees disponibles, aux temperatures pour lesquelles ces donnees existent. P O L I~ les melanges les temps de relaxation sont compatibles avec les resultats obtenus anterieurement par nous-memes et d'autres chercheurs pour des melanges liquides simples de molecules polaires en solutions dilutes. [Traduit par le journal] Can. J. Phys.. 55. 878 (1977) IntroductionThe dielectric relaxation behavior of mixtures of polar liquids is of considerable interest. However, since the initial studies by Schallamach (1946) which involved relatively complex nonrigid molecules, only a few systems have been examined. Schallamach, from his study of temperature dependence of mixtures of complex molecules at constant radio frequency, concluded that the dielectric relaxation in mixtures involves a rearrangement of relatively large regions in the liquid and if the polar conlponents in a mixture are both associative or both non-

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Section: Resultssupporting

confidence: 73%

Section: Resultssupporting

confidence: 67%

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Microwave absorption and dielectric relaxation of some rigid molecules and their mixtures

Madan¹,

Shelfoon²,

Cameron³

1977

Can. J. Phys.

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“…The evaluation of the high frequency dielectric constant (E,), distribution coefficient (a), mean relaxation time ( T~) , discrete relaxation times (T, and T,), weight factors (C, and C, ), and dipole moment (y) has been described previously (2).…”

Section: Resultsmentioning

confidence: 99%

“…Previous work (1,2) has shown that the mean relaxation times of o-xylene, m-xylene, toluene, and ethyl-, isopropyl-, and t-butyl-benzene were short in comparison with those of rigid molecules of similar shape and size (2,3). The dielectric absorption of these alkylbenzenes at 25 "C and 1-methyl-and 2-methyl-naphthalene at 50 "C was analyzed in terms of molecular reorientation and also a short relaxation time process.…”

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confidence: 99%

Dielectric studies. Part XVII. Relaxation processes and corresponding enthalpies of activation of some mono-substituted benzenes

Crossley¹,

Walker²

1968

Can. J. Chem.

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The dielectric absorption at several microwave frequencies of liquid ethylbenzene, isopropylbenzene, and phenyltrimethylsilane at 15, 37.5, and 50°C and cyclohexane solutions of t-butylbenzene and benzotrichloride at 15, 37.5,45, and 50 "C has been examined. Benzotrichloride has also been studied in cyclohexane and p-xylene solution at 25 "C. Only molecular reorientation can be detected for benzotrichloride, whereas the remainder are all characterized by an absorption that may be analyzed into two relaxation times, one associated with molecular reorientation (r,) and a shorter relaxation time (r,) which appears to be attributable to an intermolecular process. The enthalpies of activation of the rl process show the expected increase with increasing molecular size, while n o temperature dependence is detectable for the shorter relaxation process. Previous work (1, 2) has shown that the mean relaxation times of o-xylene, m-xylene, toluene, and ethyl-, isopropyl-, and t-butyl-benzene were short in comparison with those of rigid molecules of similar shape and size (2, 3). The dielectric absorption of these alkylbenzenes at 25 "C and 1-methyl-and 2-methyl-naphthalene at 50 "C was analyzed in terms of molecular reorientation and also a short relaxation time process. Furthermore, the mean relaxation times of some phenyl-substituted compounds were found to be significantly short (4), indicating a large contribution to the absorption from some short relaxation time process (z, ). Two explanations have been considered to explain T,: (a) an intermolecular process, e.g. the decay of some form of charge distortion resulting from molecular collisions, or (b) an intramolecular relaxation process involving rotation about the alkyl-aryl bond in which the overlap of the alkyl group orbitals with the TC electrons of the ring might vary. This would cause some movement of charge to and fro between the n-electron cloud of the phenyl group and the alkyl group during rotation, and implies oscillation of negative charge. The weight of evidence favored mechanism (a). However, it seemed worthwhile examining the dielectric absorption of phenyltrimethylsilane and ethyl-, isopropyl-, and t-butylbenzene over a temperature range in order to obtain the enthalpies of activation AH,' , AH, *, and AH,* associated with the mean relaxation time, T, and T, respectively, and also to determine whether the weight factor of the shorter relaxation process was temperature dependent, the main aim being to gain more information on the characteristics of the T, process. Experimental MethodsThe preparation of phenyltrimethylsilane and the purification of cyclohexane, p-xylene, and ethyl-, isopropyl-, and t-butyl-benzene have been described elsewhere (1, 4, 5). Benzotrichloride was dried over calcium chloride and fractionally distilled using a 30 theoretical plate spinning band column. A small center fraction was collected and the purity confirmed by gas-liquid chromatography.The apparatus and techniques employed have been described previously (5, 6). The dielec...

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Physical Properties of Thiophene Derivatives

Gronowitz

Hörnfeldt

1991

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Dielectric studies. Part XIX. Molecular relaxation of some rigid molecules

Cited by 13 publications

References 7 publications

Microwave absorption and dielectric relaxation of some rigid molecules and their mixtures

Microwave absorption and dielectric relaxation of some rigid molecules and their mixtures

Dielectric studies. Part XVII. Relaxation processes and corresponding enthalpies of activation of some mono-substituted benzenes

Physical Properties of Thiophene Derivatives

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