Dielectric studies. Part 14.—Mesomeric and coupled ring rotation mechanisms

Abstract

The dielectric constants and losses have been determined at five or six microwave frequencies for benzophenone, dicyclohexylketone, diethylether, diethylketone in cyclohexane solution and for decafluorobenzophenone in p-xylene. All systems except decafluorobenzophenone have definite distribution coefficients suggesting contributions from more than one relaxation process. In the absence of appreciable steric factors the measured relaxation times of symmetrical aromatic ethers and sulphides tend to be shorter than the values estimated for rigid molecules. For aromatic ethers and sulphides two intramolecular processes appear to contribute to the relaxation time shortening. One involves a mesomeric shift of charge which changes magnitude and direction during ring rotation and the other short coupled ring rotations which cause reversal of the molecular dipole moment. When the molecular moment is small (e.g., less than about 1D) the mesomeric mechanism may be significant. For benzophenone in both the pure liquid state and in a non-interacting solvent, one or both of these processes appears to give a small contribution to the dielectric absorption.