Application of the marcus relation to concerted proton transfers

Abstract

A model, based on the Marcus theory, is presented for the keto–enol tautomerism of acetone. With one adjustable kinetic parameter, the model explains the rate constants and isotope effects for the six different catalytic routes involving H₃O⁺, OH^–, H₂O, CH₃COOH, CH₃COO^– and the third-order term with both CH₃COOH and CH₃COO^–. The range of pK_A over which the third-order term is observed is also explained. General conclusions are derived and discussed concerning the catalytic advantage of the concerted mechanism described by the third-order term.