Electrochemical oxidation of some catechol (la-le) and hydroquinone (5a,5b) derivatives in the presence of arylsulfinic acids has been investigated both experimentally and theoretically to provide insight into the influence of some factors on the chemical reaction rate of electrogenerated benzoquinones with arylsulfinic acids and site-selectivity of the sulfination of some derivatives of catechol and hydroquinone. The results of this work show that the chemical reaction rate between electrogenerated o-benzoquinones and. 4-chlorobenzenesulfinic acid is dependent on the substituent group on the catechol ring. The observed homogeneous rate constants (k(obs)) of benzoquinones with 4-chlorobenzenesulfinic acid were determined using digital simulation of cyclic voltammograms. In this work, the effect of the change of Gibbs free energy of the chemical reaction and charge on the reaction site were also studied in detail. Delta G(aq) of the Michael addition reactions and charge of each site of reaction of studied species were calculated using 6-311G (p,d) basis set DFT(B3LYP, BP86) levels of theory. The results show that the charge of the reaction site not only dictates the site of reaction but also indicates the value of the homogeneous rate constants (k(obs)) of the Michael addition reaction. (C) 2013 The Electrochemical Society. All rights reserved.