Dielectric Behavior of Nonrigid Molecules. I. The Simultaneous Relaxation Mechanisms of Diphenyl Ethers and Analogous Compounds

Possible relaxation mechanisms for the anomalously rapid relaxation process in diphenyl ether and related compounds are critically examined and compared with recent experimental results. It is concluded that mechanisms involving inversion and atomic dipole are unlikely, and that shifts of electronic charge and consequent change in direction of the π-electron or mesomeric moment accompanying rotation of the rings around their bond to the rest of the molecule do not play such an important role in molecules of the diphenyl ether type as to account for the lowering of the relaxation times of these molecules. It is proposed that short coupled rotations of the rings around their bonds to the central atoms or of the C6H5X group and the other ring can change the direction of the molecular dipole moment in these molecules with much less effect upon the surrounding molecules than would be exerted by over-all molecular rotation without internal motion. A theory is described whereby such mechanisms, which give relaxation times shorter than those associated with rotation of a rigid molecule, occurring simultaneously with the over-all molecular orientation, are responsible for the observed shortening of relaxation time and must predominate over any effect of possible mesomeric moment.