Role of hydrogen bonding in the oxidation potential of enols

Three stable beta,beta-dimesityl enols with heteroaromatic rings in the a-position were synthesized to study the effect of (OHN)-N-... hydrogen bonding on the oxidation potentials of enols. In contrast to its solid-state structure, enol E1 exists predominantly as intramolecularly hydrogen-bonded species in solution. For enol E2 an intermolecular hydrogen bond and for E3 a partial proton transfer were established based on NMR, dilution experiments, solvent dependence and UV-visible spectroscopic studies. Cyclic voltammetric investigations revealed that (OHN)-N-... hydrogen bonding may shift the oxidation potentials of enols by up to 510mV cathodically. Copyright (C) 2003 John Wiley Sons, Ltd.