Proton transfer reactions hyperconjugation effects

Evidence that a 1,2-dihydroxycyclohexadienide anion is stabilized by aromatic negative hyperconjugation has been described. It complements an earlier inference of positive hyperconjugative aromaticity for the cyclohexadienyl cation. The anion is a reactive intermediate in the dehydration of benzene cw-l,2-dihydrodiol to phenol. The measurements of the solvent isotope effects are consistent with reaction via a carbanion intermediate or a concerted reaction with a carbanionlike transition state. These confirm that the reaction proceeds by a stepwise mechanism, with a change in ratedetermining step from proton transfer to the loss of hydroxide ion from the intermediate. 

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