Dielectric studies. Part XXV. Methoxy group rotation in anisole and three para-substituted anisoles

Abstract

The dielectric absorption at several microwave frequencies of anisole, p-methylanisole, and p-bromoanisole in the solvent p-xylene, and p-diniethoxybenzene in the solvent cyclohexane has been investigated at 4 to 6 temperatures. Anisole, p-methylanisole, and p-dimethoxybenzene were all found to relax mainly by methoxy group rotation, whereas the relaxation process in p-bromoanisole was very largely niolecular relaxation. In the literature, considerable divergence exists for the analyses of the dielectric data of anisole and substituted anisoles into contributions from two relaxation times and the magnitude of the weight factors governing each relaxation process. Such divergencies have been explored and justifiable analyses established for these systems where the weight factors governing the relaxation processes are shown to be roughly of the same order as those estimated from group nioment data. The weight factor for molecular relaxation in the pure liquid appears considerably greater than that for a dilute solution of it in a non-polar solvent.

Macroscopic viscosity and the dielectric relaxation of some substituted benzenes

“…The TO values (Table 1) for anisole and p-dimethoxybenzene, especially in the inore viscous solvents, are significantly shorter than those for the rigid bromobenzene. Consequently, the dielectric absorption of the two ethers must, in accord with earlier measurements (8,15,16), contain contributions from an intramolecular relaxation process, i.e. methoxy group rotation.…”

“…The errors involved in this type of analysis have been discussed in detail (14). Previous work has shown that the dielectric absorptions of the anisole and pdimethoxybenzene solutions contain contributions from two relaxation processes (8,15,16). In view of the distribution of relaxation times observed for bromobenzene, which has only one relaxation process, however, we have refrained from analyzing the data for the other systems in terms of two discrete relaxation times.…”

1,2-Rearrangement in .beta.-substituted ethyl radicals. A molecular orbital study

“…These MCSCF calculations were carried out with the iterative natural orbital/valence configuration interaction (Cl) feature of the alis19 system of programs within the molecular orbital basis size listed in Table III. All electrons (15) King, H. F.; Dupuis, M.; Rys, R. QCPE 1980, 13, 403. (16) £toui = -537.32090 au.…”

Activation energy for methoxy group relaxation

“…Molecules which liave a methoxy group attached to an aromatic ring have been widely studied by dielectric techniques (1)(2)(3)(4). The n~olecules have bee11 examined either as a pure liquid or as a solute in a dilute solution of a n o n~o l a r solvent and the a b s o r~-tion has been observed in the nlicrowave region.…”