Kinetics of dissociative electron transfer for homogeneous and heterogeneous reductive bond-breaking reactions

Abstract

The kinetics of dissociative electron transfer reactions of butyl halides by outer-sphere heterogeneous (glassy carbon electrodes) or by homogeneous (aromatic anion radicals) reagents is investigated in aprotic solvents. The potential energies of the reactants and products are described by the Morse and the exponential curves as functions of the C–X distance. Both the homogeneous and the heterogeneous reactions are consistent with an outer-sphere adiabatic electron-exchange process. The activation free energy in both cases is suitable for a quadratic driving force free energy relationship and varies with the electrode potential. The standard activation free energy contains two contributions. There is a good agreement between theory and experiment in the heterogeneous case, while the good agreement is only for the tertiary halides in the homogeneous case, which is due to the stability of tertiary radical with sterical effect.