Single-electron transfer in deacylation of ethyl dinitrobenzoates

Article abstract of DOI:10.1021/ja00181a040

Reactions of OH^- with ethyl 2,4- and 3,5-dinitrobenzoate (2,4-DNB and 3,5-DNB) in DMSO/H₂O 1:1 (v/v) involve single-electron transfer from OH^- into the antibonding orbital of the substrate to form a charge transfer complex of OH and the radical anion. This complex collapses into a tetrahedral intermediate that gives products. Nonproductive Meisenheimer complexes form and gradually disappear. The rate and equilibrium constants of the various reaction steps can be calculated by using relaxation theory. The charge transfer complexes lead to hydrogen exchange of both substrates and products in DMSO-d₆/D₂O/OD^- and ¹H signals of the esters broaden during reaction. Exchange of the carboxylate ions is slow. The 2-and 4-Mcisenheimer complexes of OD^- and 3,5-DNB are detected by ¹H NMR R spectroscopy. Semiempirical MO calculations with AM1 parameters predict that formation of charge transfer and Meisenheimer complexes, and of the tetrahedral intermediate, is enthalpically favored in the absence of solvent interactions and hydration of OH^- is a significant barrier to reaction.