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epoc ABSTRACT: Three stable ,-dimesityl enols with heteroaromatic rings in the -position were synthesized to study the effect of OH Á Á ÁN 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 Á Á ÁN hydrogen bonding may shift the oxidation potentials of enols by up to 510 mV cathodically. RESULTS AND DISCUSSIONEnols E1-E3 were prepared by the reaction of ,dimesitylketene 8 with the corresponding heteroaryl lithium reagent, in yields ranging from 24 to 40%. They were fully characterized by 1 H and 13 C NMR, IR and elemental analysis. Moreover, the solid-state structure of E1 (see below) confirms the enol structure of E1-E3.

Almost completely unknown—the chemistry of radical dications. A reactive intermediate of this type (1•2+) plays a key role in the oxidative rearrangement of the persistent cation 1+.

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