Role of hydrogen bonding in the oxidation potential of enols

Three stable β,β-dimesityl enols with heteroaromatic rings in the α-position were synthesized to study the effect of OH···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 OH···N hydrogen bonding may shift the oxidation potentials of enols by up to 510 mV cathodically. Copyright © 2003 John Wiley & Sons, Ltd.