The anodic oxidation of N,N-dimethyl-p-toluidine (2) was studied using cyclic voltammetry and spectroelectrochemistry. In contrast to former studies, the experimental measurements showed that the radical cations of 2 reversibly dimerize at the methyl substituted p-position of the dimethylamino group and form a-dimers. Theses results again clearly demonstrate that or-dimerization takes place even when reactive sites are blocked by substituents such as alkyl or phenyl groups. The findings are also relevant for the interpretation of a-dimerization during electropolymerization and charging of conducting polymers. (c) 2007 Elsevier Ltd. All rights reserved.