Eyring activation barriers for the anomalous dielectric relaxations of diphenyl ether-type molecules

Chao, Jessie Lorenzo; Desando, M. A.; Gourlay, D. L.; Orr, D. E.; Walker, S.

doi:10.1021/j150648a019

Cited by 12 publications

(9 citation statements)

References 4 publications

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“…There are considerable similarities between the behaviour of the long-chain alcohols and the corresponding aldehydes and 1 -bromoalkanes. The intramolecular nature of the low-temperature absorption is also borne out by the similar values of / 3 (0.23-0.34) for intramolecular relaxation of some symmetrically substituted diaryl ether compounds in the temperature range 83-141 K. 36 The smallest molecule we studied was n = 3 (n-pentanol). Only one absorption peak has been detected for n = 3, and the likely mechanism is either intramolecular or an overlap of molecular and intramolecular processes.…”

Section: Low-temperature Dielectric Absorption Of the Alkan-1-01smentioning

confidence: 59%

Dielectric relaxation of alkan-1-ols and 1-thiols in a polystyrene matrix

Huque¹,

Walker²

1986

J. Chem. Soc., Faraday Trans. 2

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Dielectric absorption studies have been made on numerous alkan-1-01s and l-thiols dispersed in a polystyrene matrix in the frequency range 10-105 Hz between 80 and 300 K. With the exception of pentan-1-01 a loss factor vs. temperature plot at a fixed frequency clearly reveals two separated absorption peaks in this medium. The lower-temperature process may be accounted for by an intramolecular process where various segments of the chain rotate about the C-C bonds accompanied by movement of the main dipole ( -CH2X where X = OH and SH). This intramolecular relaxation process needs to be taken into account when the various relaxation motions exhibited by alcohols are considered, whereas previously only the OH group relaxation itself has been postulated. At the relatively low concentrations employed the energy of activation parameters for the low-temperature process seems reasonably independent of the nature of the main dipole (X = OH, SH, Br). Comparison of the high-temperature process with that of the corresponding 1 -bromoalkanes suggests the presence of some intermolecular hydrogen bonding in the case of the alkan-1-01s but not in the l-thiols.

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Section: Low-temperature Dielectric Absorption Of the Alkan-1-01smentioning

confidence: 59%

Dielectric relaxation of alkan-1-ols and 1-thiols in a polystyrene matrix

Huque¹,

Walker²

1986

J. Chem. Soc., Faraday Trans. 2

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“…The potential surface described by +I and is not available experimentally, although 13C nmr spin-lattice relaxation times for a chloroform solution have been interpreted to mean that the barrier to internal rotation is 10.2 kJ/mol for the phenyl groups (2). This number is similar to the 10 kJ/mol estimated for the enthalpy of activation from dielectric relaxation studies on diphenyl ether dispersed in a polystyrene matrix (3). Ab initio computations of this surface seem not to be available.…”

Section: Introductionmentioning

confidence: 73%

Remarks on the internal motion in diphenyl ether. Fluorophenyl ethers

Schaefer¹,

Penner²,

Takeuchi³

et al. 1988

Can. J. Chem.

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and POTLAKI TSEKI. Can. J. Chem. 66, 1647Chem. 66, (1988. The I3C nuclear magnetic resonance chemical shifts and the I3C,l9F spin-spin coupling constants are reported for 4,4'-difluorophenyl ether and 4-fluorophenyl phenyl ether in CS, and in acetone-d6 solutions. An estimate of 6~9 0 , the extremum in the a-T coupling constant between the I9F nucleus on one ring and the ips0 I3c nucleus on the other, is obtained from measurements on 2,6-dibromo-4-fluorophenyl phenyl ether. The ensuing estimates of (sin' 0), the expectation values of sin2 0 as obtained from 6~( 1 3 C , 1 9~) , are compared with those obtained from STO-3G MO computations for diphenyl ether and its 4-fluoro derivatives. These computations give conformational energies at 30" intervals of the angles of twist about the two C-0 bonds. In rough agreement with C-INDO computations, interconversion of the helical forms is calculated to occur most easily by the so-called one-ring flip mechanism; the barrier to interconversion is less than 1 kJ/mol in the ether and its 4-fluoro derivatives. It appears that the conformational behaviour of these derivatives is unaltered by passage from CSZ to acetone solutions at 300 K. Furthermore, (sin' 0) values from 6~( 1 3~, 1 9~) in solution are very similar to those obtained from the computations on the free molecules. If this agreement is not accidental, then it may arise from a high degree of flexibility of the molecules in which, by a disrotatory or one-ring flip mechanism requiring a very low energy of activation, one helical or C2 conformation can be converted to another. The other conformations have considerably higher energies and the solvents do not appear to lower these energies enough to favor their populations significantly at 300 K. [Traduit par la revue]

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“…For the structures of most PBDEs (see Figure 1), the barrier of internal rotation of phenyl rings around the neighbouring C-O bonds was experimentally suggested to be too low to retain the molecular conformation rigidity [40,41]. As indicated in previous studies, some PBDEs have two or three more conformational isomers except for those with high symmetry [29,31].…”

Section: Computation Of Electronic Properties By Dftmentioning

confidence: 83%

DFT study on the bromination pattern dependence of electronic properties and their validity in quantitative structure–activity relationships of polybrominated diphenyl ethers

Jiang

et al. 2009

SAR and QSAR in Environmental Research

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With quantum chemical computation of density functional theory (DFT), the electronic properties including the polarisabilities, polarisability anisotropies and quadrupole moments of a total of 209 congeners of polybrominated diphenyl ethers (PBDEs) were evaluated. The electronic properties were shown to be highly dependent on the bromination pattern, i.e. their values changed sensitively with the number and sites of bromination. Being similar to the 2,3,7,8-, 1,4,6,9-chlorination of dioxins, respectively, 3,3',4,4'-, 2,2',5,5'-bromination of PBDEs can impose relatively greater effects on the electronic properties. Some of electronic properties were found to be potent in explaining the variance of toxicity, and the potency was verified by the development of quantitative structure-activity relationships (QSARs). To further improve the stability and predictability of QSARs for toxicity, two-dimensional topological indices were introduced. In QSARs, polarisability anisotropy was more significant than other polarisability tensors, indicating the implicit occurrence of dispersion interaction between the ligand and aryl hydrocarbon receptor (AhR). For PBDEs, the quadrupole moment was as significant as shown previously for dioxins. As interesting descriptors with encoded information about dispersion and electronics, the electronic properties analysed herein are helpful in obtaining a better understanding of the congener-specific toxicities of PBDEs, and are applicable and may be extended to research into the toxicology of structurally similar compounds, such as halogenated aromatics.

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Eyring activation barriers for the anomalous dielectric relaxations of diphenyl ether-type molecules

Cited by 12 publications

References 4 publications

Dielectric relaxation of alkan-1-ols and 1-thiols in a polystyrene matrix

Dielectric relaxation of alkan-1-ols and 1-thiols in a polystyrene matrix

Remarks on the internal motion in diphenyl ether. Fluorophenyl ethers

DFT study on the bromination pattern dependence of electronic properties and their validity in quantitative structure–activity relationships of polybrominated diphenyl ethers

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