THEORETICAL-STUDY OF HOMOGENEOUS ELECTRON SELF-EXCHANGE IN POLAR AROMATIC-MOLECULES - THE ROLE OF THE REACTANT STRUCTURE

The solvent reorganization energies lambda0 of the electron self-excha nge reaction between neutral molecules (nitrobenzene, its five para-su bstituted derivatives and benzonitrile) and the corresponding radical anions are discussed in terms of the Kirkwood approach combined with a semi-empirical calculation of the reactant structure (AMI and interme diate neglect of differential overlap (INDO) methods). The theoretical values of lambda0 are compared with the experimental reorganization e nergies lambda calculated from the Marcus equation and the homogeneous rate constants k(ex). It is found that the values of lambda0 obtained using the INDO method are approximately equal to the experimental lam bda, whereas the AMI method gives poor results for para-substituted ni trobenzenes. The linear correlation of log k(ex) with a(N)2 where a(N) is a nitrogen coupling constant, established for para-substituted nit robenzenes is interpreted. A simple criterion for slow electron transf er of an arbitrary flat polar arene is formulated in terms of the reac tant structure and the model of the ''specifying group'' suggested ear lier by some of the authors.