NMR investigation of rotation about carbon-carbon double-bond : Kinetic and thermodynamic aspects of isomerization of conjugated ketene-mercaptoaminals

Abstract

The thermal isomerization rates of several conjugated ketene-mercaptoaminals involving rotation about a CC double bond were found to be within the NMR time scale. Activation energies for the above process were determined from variable temperature NMR studies. The effects of various structural parameters on the energy barrier for isomerization were investigated and the contribution of the vinylic methylthio group to the above barrier was estimated. Internal H-bonding was found to have a pronounced effect on the rates of isomerization. Diastereomeric stabilities in suitably substituted systems were also determined.