OUTER-SPHERE ELECTRON-TRANSFER REACTIONS, RARE EVENTS IN ORGANIC-CHEMISTRY

Attempts to find authentic cases of outer-sphere electron transfer reactions involving at least one organic component are described. It is concluded that heteropoly anions, large, spherical anions exposing only non-nucleophilic and at worst weakly basic oxygens toward the solution phase, oxidize aromatic substrates via an outersphere electron transfer step. Comparison with other reactions, such as oxidations by Fe(III) and Ru(III) complexes and hexachloroosmate(V) ion, reveals a consistent pattern of reactivities. The most important conclusion is that reorganization energies of organic self-exchange reactions (RH+./RH), estimated via the Marcus treatment, are significantly larger than those measured directly from the kinetics of self-exchange. This is ascribed to electronic interaction in the transition state of self-exchange of (RH+./RH), amounting to 5 kcal mol-1 or more.