Abstract: The mechanism of aryl participation in the formolysis of 4-aryl-n-butyl p- bromobenzenesulfonates has been elucidated by the study of suitably deuterated substrates. The formolysis of 4-(p-methoxyphenyl)-n-butyl-2, 2-d2 p-bromobenzenesulfonate proceeded 74.2 z by Ari-5 and 25.8% by Ar2-6, in contrast to earlier assumptions of an exclusive Arl-5 pathway. The formolysis of the bromobenzenesulfonate of 4-(p-tolyl)-n- ...