Linear free energy relationship for the pressure dependence of rate constants in ene reactions

Abstract

The effect of pressure on rate constants of ene reactions involving (C ⋯ H ⋯ O), (C ⋯ H ⋯ C) and (O ⋯ H ⋯ O) hydrogen transfer is described by an equation of the linear free energy relationship type. Characteristic parameters of the equation are rather close to those obtained earlier for other types of nonpolar reactions with transition states involving the formation of new bonds. Activation volumes are calculated more precisely as compared with the commonly accepted methods, thus allowing us to find a strong linear dependence of activation volume on the logarithm of the rate constant in the reaction series of alk-1-enes with dimethyl mesoxalate. The reaction volume profile is described, its estimated parameters being in line with the experimental ones according to the accepted mechanism. The calculations point to processes which are not fully concerted.