Hydrogen-bond basicity of push–pull α,β-unsaturated enaminoketones

Abstract

A method is proposed for evaluating the hydrogen-bond basicity of certain conformers of two push–pull enaminoketones with the general formula R C(O) CH CH N(CH 3) 2, where R=CH 3 (DMBN); R=CF 3 (DMTBN). It has been shown, for both enaminoketones, that the ( EE) conformer has a higher basicity than the ( EZ) conformer. Moreover, the (DMBN) has one of the highest general p K HB values in the hydrogen-bond basicity scale of ketones. Substitution of the CH 3-group in (DMBN) with the CF 3-group in (DMTBN) reduces general p K HB sharply as a consequence of electron withdrawal of CF 3-group. Hydrogen bond sites are also discussed; it is shown that, in both enaminoketones, carbonyl oxygen possesses the maximal basicity, whereas nitrogen of the dimethylamino group has less basicity, and the vinyl moiety is the least basic site. Enthalpies of hydrogen bond formation (−Δ H) in absolute values, as well as the respective p K HB values, are greater for the ( EE) conformer than for the ( EZ) as a consequence of greater contribution of resonance structure in the ( EE) form. ▪