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

The kinetics of dissociative electron transfer reactions of butyl halides b y 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 homo geneous and the heterogeneous reactions are consistent with an outer-sphere adiabatic electron-exchange process. The activation free energy in both ca ses is suitable fora quadratic driving force free energy relationship and v aries with the electrode potential. The standard activation free energy con tains two contributions. There is a good agreement between theory and exper iment in the heterogeneous case, while the good agreement is only for the t ertiary halides in the homogeneous case, which is due to the stability of t ertiary radical with sterical effect. (C) 2000 Elsevier Science B.V. All ri ghts reserved.