Abstract During SET oxidation of the title compound, N, N, N′-trimethyl-N′-(4- methoxyphenyl)-1, 4-phenylendiamine radical cation (3a+.) was detected by esr; this derives from an oxidatively activated nucleophilic substitution on N, N-dimethyl-p-anisidine. Revised esr parameters for N, N-dimethyl-p-anisidinium radical are also reported.