Stereochemistry of electrode reactions

Abstract

Two aspects of the stereochemistry of electrode reactions are considered: (i) fast electrode reactions that do not involve significant structural changes. This criterion is applied to decide the most probable conformation of the green (thermochromic) form of dehydrodianthrone, based on the polarography of the system dehydrodianthrone + dianthranol. The system, benzil (XI)+ stilbenediols (cis, IX, and trans, X) with an equilibrium conformation of benzil at the site of electron transfer determining electrode reaction rates, is analogously considered. (ii) In slow electrode reactions involving a fission of a stable σ-bond, e.g., a C—Cl bond, the stereochemistry of the reaction determines the mechanism. At a Hg cathode each of the stereoisomers of 2-phenyl-2-chloropropionic acid is reduced to an optically active 2-phenylpropionic acid with 80–90 % inversion of configuration. Stereochemical evidence supports a S_N²-like mechanism of the electrode process.