MEDIUM EFFECTS IN THE ELECTROREDUCTION OF BENZOPHENONE IN APROTIC-SOLVENTS

The kinetics of electroreduction of benzophenone have been studied at a mercury ultramicroelectrode in seven aprotic solvents. In addition, the temperature dependence of the standard rate constant was determine d in three solvents, and the effect of tetraalkylammonium cations on t he kinetic parameters was assessed in acetonitrile. On the basis of an analysis of the solvent effects, it is shown that this fast electron- transfer reaction is adiabatic. A model for solvation of the activated complex based on three contiguous spheres corresponding to the two ph enyl rings and the carbonyl group is described and used to assess the outer-sphere contribution to the Gibbs activation energy for electron transfer.