Motional Disorder in Hexasubstituted Chloromethylbenzenes

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Abstract
The nuclear magnetic relaxation times T1 and T1ρ have been measured for protons in three solid hexasubstituted chloromethylbenzenes, 1,2,3-trichlorotrimethylbenzene, dichlorodurene, and tetrachloroparaxylene, from 77°K to their melting points. The results are interpreted in terms of in-plane molecular reorientation in the upper temperature range and methyl group reorientation in the lower temperature range. Activation enthalpies for these motions are obtained, and the effect of substituting chlorine atoms for methyl groups in hexamethylbenzene is discussed. It has been found necessary to invoke a distribution of correlation times to account for the measurement of in-plane reorientation in all samples studied. The results for 1,2,3-trichlorotrimethylbenzene are compared with those obtained by dielectric relaxation studies.