Unstable intermediates. Part XXXVI. The hexamethylbenzyl cation-radical

Abstract

Hexamethylbenzene reacts slowly with concentrated sulphuric acid to give a stable cation-radical characterised by an electron spin resonance spectrum consisting of a major triplet assigned to two equivalent protons with a hyperfine coupling constant of 5·4 gauss. Two other sets of protons cause further splitting, one coupling constant being 1·7 gauss and the other nearly twice as large. In deuteriosulphuric acid the two strongly interacting protons exchange rapidly but the remainder are unaffected. The same radical is formed from pentamethylbenzene in sulphuric acid and also by reaction with aluminium chloride. These results are interpreted in terms of the hexamethylbenzyl cation formed by oxidation of the heptamethylbenzenium cation known to be readily formed in these solutions.