Substituent effects on the reaction kinetics of electrogenerated 9-substituted 10-phenylanthracene cation radicals with water and methanol

Substituent effects on the reactions of electrogenerated anthracene derivative cation radicals with water and methanol were studied systematically by using a pulse-electrolysis stopped-flow method. Five 9-substituted 10-phenylanthracene cation radicals (XPA^.+) were produced electrochemically, and their reaction kinetics were investigated. In all the reactions, the rate law was found to be first-order in XPA^.+ and second-order in water and methanol. The reaction rate varied greatly depending on the nature of the substituents. While the electrochemical and spectroscopic properties of XPA^.+ were correlated to the results of simple Hückel molecular orbital calculation, the order of the reaction rates was explained by the coulombic interaction induced by the substituents on the basis of the reaction mechanism and taking into account the particular conditions. The coulombic interaction caused by the substituents seems to be a significant factor governing the reactivities of aromatic cation radicals.