On the deprotonation of the cation radicals of substituted ethylenes. A heterolytic or homolytic process?

The deprotonation of several cation radicals of substituted ethylenes in a monohydrated, monoammoniated or dihydrated cluster has been theoretically studied using an ab initio method through the 6-31G(D, P) basis set. It has been found that the cation radicals are π radicals, whereas the corresponding deprotonated species are σ radicals, the deprotonation process involving an intramolecular electron transfer from a σ to a π molecular orbitals. The experimental findings about the deprotonation reactions of organic cation radicals that have charge delocalized from the departing proton have been confirmed. The dissociation of the carbon-hydrogen bond begins with the homolytic stretching of the C-H bond and then becomes a heterolytic dissociation, the transition state appearing very near the region of the crossing between both diabatic potential energy surfaces. The global proton transfer can therefore be described as a concerted transfer of a hydrogen atom and an electron in opposite senses.