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

1968 ◽  
Vol 46 (12) ◽  
pp. 2181-2185 ◽  
Author(s):  
J. Crossley ◽  
W. F. Hassell ◽  
S. Walker
Keyword(s):  
Dipole Moments ◽  
Relaxation Times ◽  
Major Axis ◽  
Distribution Coefficients ◽  
Solvent Interactions ◽  
Zero Distribution ◽  
Nonpolar Solvents ◽  
Dielectric Absorption ◽  
Local Environments ◽  
Distribution Parameters

The dielectric absorption at five microwave frequencies of solutions of seven rigid polar molecules in nonpolar solvents has been examined as also has cyclohexanone. Furan, pyridine, and thiophene have their dipole moments along the major axis and their dielectric absorption should be characterized by a single relaxation time. Unlike the monohalobenzenes, camphor, pentamethylene sulfide, tetrahydropyran, and s-trioxan, however, furan, pyridine, and thiophene have non-zero distribution coefficients at 25 °C, whereas for pyridine at 50 °C and cyclohexanone at 25 °C the value is zero. The non-zero distribution coefficients are to be related to either weak solute-solute or solute-solvent interactions, resulting in the polar molecule experiencing a variety of local environments. The observed relaxation times of furan, pyridine, and thiophene are comparable with those of other rigid molecules of similar shape and size. For such cases, even though the distribution parameters are not zero, it is not feasible to analyze the dielectric data into contributions from more than one relaxation process.

Dielectric relaxation of acetyl- and benzoyl-acetones

1989 ◽  
Vol 67 (5) ◽  
pp. 804-808 ◽  
Author(s):  
R. K. Khanna ◽  
Abha Bhatnagar
Keyword(s):  
Dielectric Relaxation ◽  
Dipole Moments ◽  
Relaxation Times ◽  
Weight Fraction ◽  
Relaxation Mechanism ◽  
Relaxation Processes ◽  
Dielectric Absorption ◽  
Molar Polarization ◽  
Distribution Parameters ◽  
Few Data

Dielectric absorption measurements are reported at radio and microwave frequencies (at six different wavelengths) for acetylacetone and benzoylacetone solutions in benzene, in a temperature range 25–60 °C. Analysis of dielectric data in terms of Cole–Cole arc plots and multiple relaxation processes reveals that, at higher temperatures, overall molecular relaxation is the dominant relaxation mechanism in these β-diketones. The observed relaxation times, distribution parameters, and dipole moments are in reasonable agreement with the few data reported for some temperatures, in the literature. The activation energy parameters are also evaluated assuming dielectric relaxation to be a rate process. Molar polarization vs. weight fraction (concentration) plots show anomalous behaviour for acetylacetone. Keywords: dielectric properties, dielectric losses, relaxation times, dipole moment, dielectric absorption and dispersion, microwave measurements.

Dielectric Relaxation of Bromoalkanes in Cyclohexane Solution

1972 ◽  
Vol 50 (13) ◽  
pp. 2031-2034 ◽  
Author(s):  
Sing Pin Tay ◽  
John Crossley
Keyword(s):  
Dielectric Constant ◽  
Dielectric Relaxation ◽  
Dipole Moments ◽  
Relaxation Times ◽  
Dielectric Constant And Loss ◽  
Distribution Parameters

Mean relaxation times, Cole–Cole distribution parameters and apparent dipole moments, obtained from dielectric constant and loss measurements at 2 MHz and 1.5, 2.0, 2.5, 9.3, 16, 24, 35, 70, and 145 GHz, are reported for 1-, 2-, and 4-bromooctane, 1-bromodecane, 1-bromododecane, 1-bromohexadecane, 1-bromooctadecane, and 1,10-dibromodecane in cyclohexane solution at 25 °C.

Dielectric studies. Part XVIII. Dipole moments and relaxation times of some symmetrically substituted alkylbenzenes

1968 ◽  
Vol 46 (6) ◽  
pp. 847-851 ◽  
Author(s):  
J. Crossley ◽  
S. Walker
Keyword(s):  
Relaxation Time ◽  
Dipole Moments ◽  
Relaxation Times ◽  
Pure Liquid ◽  
Dielectric Studies ◽  
Molecular Reorientation ◽  
Microwave Frequencies ◽  
Short Relaxation Time ◽  
Dielectric Absorption ◽  
Liquid Benzene

The dielectric absorption at four microwave frequencies of pure liquid benzene and p-cymene at 25 °C, p-xylene and mesitylene at 25, 40, 50, and 60 °C, and solutions of durene and hexamethylbenzene in mesitylene at 60 °C has been examined. All show measurable loss factors and apparent dipole moments of about 0.1 to 0.2 D. These moments are less in magnitude than those associated with the short relaxation time (τ2) process for the polar monoalkylbenzenes. o-xylene and m-xylene. Their relaxation times are too short for molecular reorientation and there is a rough correlation between the number of collisions/molecule s and the reciprocal relaxation time.

Dielectric Relaxation of Alkyl Acetates in Aromatic and Aliphatic Solvents at Microwave Frequencies

1972 ◽  
Vol 50 (13) ◽  
pp. 1449-1452 ◽  
Author(s):  
G. P. Srivastava ◽  
P. C. Mathur ◽  
Mrs. Krishna
Keyword(s):  
Dielectric Relaxation ◽  
Dipole Moments ◽  
Relaxation Times ◽  
Strong Interactions ◽  
Dielectric Relaxation Time ◽  
Methyl Ethyl ◽  
Microwave Frequencies ◽  
Aromatic Solvents ◽  
Nonpolar Solvents ◽  
Alkyl Acetates

The dielectric relaxation times and the dipole moments of methyl, ethyl, and amyl acetates are measured in six nonpolar solvents having different viscosities. The dielectric relaxation time is found to increase with the chain length in each nonpolar solvent. The relaxation times in aromatic solvents (benzene and p-xylene) are found to be higher than in carbon tetrachloride, even though the viscosity of the latter is more than that of the aromatic solvents This shows that the dielectric relaxation is not only due to the viscous resistance of the solvent but is also influenced by strong interactions between aromatic solvents and solute molecules.

Conformation and electronic structure of aromatic chloroformates

1987 ◽  
Vol 52 (4) ◽  
pp. 970-979 ◽  
Author(s):  
Otto Exner ◽  
Pavel Fiedler
Keyword(s):  
Electronic Structure ◽  
Oxygen Atom ◽  
Strong Interaction ◽  
Electron Distribution ◽  
Room Temperature ◽  
Functional Group ◽  
Dipole Moments ◽  
Carbonyl Oxygen ◽  
Nonpolar Solvents ◽  
Single Method

Aromatic chloroformates Ib-Ie were shown to exist in the ap conformation, in agreement with aliphatic chloroformates, i.e. the alkyl group is situated cis to the carbonyl oxygen atom as it is the case in all esters. While 4-nitrophenyl chloroformate (Ie) is in this conformation in crystal, in solution at most several tenths of percent of the sp conformation may be populated at room temperature and in nonpolar solvents only. A new analysis of dipole moments explained the previous puzzling results and demonstrated the impossibility to determine the conformation by this single method, in consequence of the strong interaction of adjoining bonds. If, however, the ap conformation is once proven, the dipole moments reveal some features of the electron distribution on the functional group, characterized by the enhanced polarity of the C-Cl bond and reduced polarity of the C=O bond. This is in agreement with the observed bond lengths and angles.

Relaxation processes of some simple aliphatic molecules in dilute solutions

1977 ◽  
Vol 55 (4) ◽  
pp. 297-301 ◽  
Author(s):  
M. P. Madan
Keyword(s):  
Carbon Tetrachloride ◽  
Dielectric Relaxation ◽  
Thermodynamic Parameters ◽  
Relaxation Times ◽  
Relaxation Processes ◽  
Dilute Solutions ◽  
Microwave Region ◽  
Nonpolar Solvents ◽  
Dielectric Data ◽  
Intramolecular Rotation

The dielectric relaxation processes of acetone, cyclohexanone, 4-methyl-2-pentanone, and 4-heptanone in dilute nonpolar solvents, n-heptane, cyclohexane, benzene, and carbon tetrachloride have been studied in the microwave region over a temperature range 10 to 60 °C. The relaxation times and the thermodynamic parameters for the activated states have been determined using the measured dielectric data. The results have been discussed in terms of dipole reorientation by molecular and intramolecular rotation and compared, wherever possible, with other similar studies on aliphatic molecules.

Relaxation processes of quinoline, isoquinoline, and their mixtures

1980 ◽  
Vol 58 (1) ◽  
pp. 20-24 ◽  
Author(s):  
M. P. Madan
Keyword(s):  
Thermodynamic Parameters ◽  
Molecular Motion ◽  
Polar Solvent ◽  
Relaxation Times ◽  
Relaxation Processes ◽  
Polar Components ◽  
Dielectric Absorption ◽  
System A ◽  
Dielectric Data ◽  
Activated State

The dielectric absorption of quinoline, isoquinoline, and their binary mixtures has been studied in the microwave region over a range of temperatures in dilute benzene and n-heptane solutions. The relaxation times and the thermodynamic parameters for the activated state have been determined using the measured dielectric data. The results obtained have been discussed in terms of the molecular motion of the system. A relation has been proposed to represent the relaxation behavior of a system of two Debye-type polar components in a non-polar solvent. The relation has been tested by comparing the calculated values with those determined experimentally for a few systems consisting of similar, simple rigid polar molecules.

Bonded Hydrogen and Trapped H2 in a-Si1−xGex:H Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
E. J. Vanderheiden ◽  
G. A. Williams ◽  
P. C. Taylor ◽  
F. Finger ◽  
W. Fuhs
Keyword(s):  
Temperature Dependence ◽  
Molecular Hydrogen ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Local Environments

ABSTRACT1H NMR has been employed to study the local environments of bonded hydrogen and trapped molecular hydrogen (H2) in a series of a-Si1−xGex:H alloys. There is a monotonic decrease of bonded hydrogen with increasing x from ≈ 10 at. % at x = 0 (a-Si:H) to ≈ 1 at. % at x = 1 (a-Ge:H). The amplitude of the broad 1H NMR line, which is attributed to clustered bonded hydrogen, decreases continuously across the system. The amplitude of the narrow 1H NMR line, which is attributed to bonded hydrogen essentially randomly distributed in the films, decreases as x increases from 0 to ≈ 0.2. From x = 0.2 to x ≈ 0.6 the amplitude of the narrow 1H NMR line is essentially constant, and for x ≥ 0.6 the amplitude decreases once again. The existence of trapped H2 molecules is inferred indirectly by their influence on the temperature dependence of the spin-lattice relaxation times, T1. Through T1, measurements it is determined that the trapped H2 concentration drops precipitously between x = 0.1 and x = 0.2, but is fairly constant for 0.2 ≤ x ≤ 0.6. For a-Si:H (x = 0) the H2 concentration is ≈ 0.1 at. %, while for x ≥ 0.2 the concentration of H2 is ≤ 0.02 at. %.

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