Publisher Summary This chapter focuses on the electron transfer reactions in organic chemistry. The simplest elementary act in homogeneous solution chemistry is the exchange of an electron between two chemical entities. No bonds need to be formed or broken in the process, and if the two species are identical, except for a difference in oxidation state, no net chemical change takes place. Such self-exchange reactions constitute the basis of theoretical treatments of electron transfer. A more complex and chemically interesting situation is the electron-transfer reaction between two species of different chemical composition. In electron-transfer theory, it is an important postulate that electrons are transferred one by one, which does not mix well with the two-electron centered electronic theory of organic molecules. Organic electron transfers rarely occur as isolated steps because of the high chemical reactivity of odd-electron species. Processes involving one or several electron-transfer steps are not likely to preserve the stereochemical integrity of the reactants. With the present upsurge of research studies frequently invoking organic electron-transfer steps in mechanistic discussions, there is a great need of a theoretical background applicable to organic species and compatible with the language of physical organic chemistry.

Electron transfer reactions in organic chemistry

Dimerization, disproportionation and e.c.e. mechanisms in the reduction of aromatic carbonyl compounds in alkaline media

New aspects of the electrochemistry of heteropolyacids: Part IV. Acidity dependent cyclic voltammetric behaviour of phosphotungstic and silicotungstic heteropolyanions in water and N,N-dimethylformamide

Homogeneous vs. heterogeneous electron transfer in electrochemical reactions

Disproportionation during electrooxidation of catecholamines at carbon-fiber microelectrodes

Homogeneous electron exchange rates, determined by a modified e.s.r. method in both the slow and fast exchange limits, are compared with published heterogeneous rates at mercury for aromatic hydrocarbon reduction in dimethylformamide; the ratio is approximately constant. This constant can be derived from theories of Marcus and Hush on a model in which image forces are negligible in the electrode process and homogeneous exchange occurs only on contact. Potential-step methods are used to study the source of electrons transferred to radicals formed by protonation of the hydrocarbon radical anions (e.c.e. mechanism) : electron transfer occurs from other radical anions for anthracene and from the electrode for naphthalene. This result is interpreted in terms of relative rates of cross-exchange reactions as predicted by Marcus theory from the “isotopic” exchange rates and redox potentials of the systems. General considerations imply that cross-exchange reactions will predominate in many aromatic systems. Proton addition from phenol to the radical anions appears to involve direct contact of acid and base rather than the free (solvated) proton.

M. E. Peover

Papers

Homogeneous and heterogeneous electron exchange in the reduction of aromatic hydrocarbons

Homogener und heterogener elektronenaustausch bei der red. aromatischer kohlenwasserstoffe