~ I I C R O I Y ~ i VllBSORPTIOS E A I D JLOI,ECUI,,2lt STIiKCTT‘IIE I N LIQKIDS. XXS1. ASALYSIS I N TERMS OF TIYO RELSXBTIOS TIMES FOB SOME AROMATIC ETHERS’ BY KLATX BERGXWN. DoamIc 31. ROBERTI~ A N D CHARLES E‘. SMYTH (“f,n~?ihi/t?Ou
f r o m the F r i t k Chemcnl Laboratory, Princeion (‘nil ersily, I’tinceton, S. J . Xecerved Dwemhrr 19, 1979
Dielectric measurements nn diphenyl ether, dibenzj 1 ether, anisole and o-dimethoughenzene have heen analyzed in terms of two relauation times. The results are consistent mith the interprrtation of a large relaxation time due to molecular rotation and a smaller rc,laxation time due to intramolecular motion, notably methosy group rotation for anisole and 0tlimethoxybenzene. The data for dibenzyl ether have also been analyzed in terms of a distribution of relaxation times betveen two limiting values.
The Cole-Cole arc plot has proved a very iiseful mcthod CJC representing the relationihip between dielectric constant and dielectric loss and of calculating dielectric relauation time. Its assumed symmetrical distribution of relaxation timrs around a most probable value commonly cannot be (1istinguisht:d by the few points experimentally ohtainnble a t niicrowave frequencies from other possible distributions. Considerations of structure in some cases render more probable a distribution of relaxation times between two limiting ~ n l u e s . ~A number of relaxation times have been found which are much lover than mould be exprcted for the molecules in the media in question. -Ilthough, in several of these cases, the deviation of‘ the observed points from a Cole-Cole arc iy little, if any, greater than the possible experimental error, it appears certain that the dielectric relaxation proccss iiivolves an intramolecular orientation process with n very short relaxation time in addition to the normal molecular orientation process. The extent to which the observed relaxation time is shortened below that to be expected for the molecular orientation process depends upon the relative importance of the intramolecular process. Jt is the purpose of the present paper to analyze the dielectric relaxation of certain of these substances in terms of two relaxation times, one for the molecular orientation process and one for the intramolecular. If there are tivo relaxation times and one is much larger than the other, the two dispersion regions are distinct, and each may be examined independently of the other.5 More often there is overlapping of the dispersion regions and the observed relaxation time is lower than would be expected from the size of the molecule, as Fischer6 found for diphenyl ether. A previously described7 indirect method of analysis for such a case has been applied to measurements on four aromatic ethers. (1) This research h a s been supported in part by t h e United States Ail Force through t h e Office of Scientific Research of t h e Air Research a n d Development Command under Contract No. A F 18(600)1331. Reproduction, translation, publication, use or disposal in whole o r in part by or for t h e United States Government is permitted ( 2 ) Gulf Oil Fellow in Chemistry. 1967-1958. ( 3 ) H. E rohlich, “Theoiy of Dielectrics,” Oxford University Press, Lonaon, 1949, I). 94. (4) K. Higas:. K. Bergmann a n d C. P. Smyth, t o be puhlislied. ( 5 ) M. Davlrs and R. J. hieakins, J. Chem. P I L ~ J26, ~ . ,1584 (1957). ‘6) E. Fischer, %. Xoturforsch. 4A. 707 (1949). i) I
