Unusual reaction of bromoalkyl trifluoromethyl ketones with symmetrically disubstituted ethylenediamines. Theoretic investigation applying methods of density functional and multiparticle perturbation theory МР-2

Resumo

Mechanism of a multistage reaction between α-bromotrifluoromethylenones and N,N′-dialkylethylenediamines was examined in detail using quantum chemical methods of density functional (non-empirical functional РВЕ, extended split TZp-basis) and multiparticle perturbation theory МР-2, basis 6-311+G(d,p), in the gas phase approximation, and also including solvents molecules (water and 2,2,2-trifluoroethanol). The specific solvation of transition states owing to the hydrogen bonds formation with solvent molecules is the main factor governing the direction of the reaction. Trifluoroethanol forms a strong H-bond with the carbonyl oxygen atom of the trifluoroacetyl group increasing its electrophilicity. It also solvates the departing bromide anion facilitating the occurrence of the S_N2-substitution reaction. An essential but less important factor is the ability of trifluoroethanol to play the role of a nucleophilic partner by forming hydrogen bonds at the expense of the unshared electron pair of the hydroxyl oxygen facilitating the proton abstraction from the nitrogen atom of the diamine attacking the carbon atom in the course of S_N2-substitution.