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 duster has been theore tically studied using an ab initio method through the 6-31G(D, P) basi s set. It has been found that the cation radicals are pi radicals, whe reas the corresponding deprotonated species are sigma radicals, the de protonation process involving an intramolecular electron transfer from a sigma to a pi molecular orbitals. The experimental findings about t he deprotonation reactions of organic cation radicals that have charge delocalized from the departing proton have been confirmed. The dissoc iation of the carbon-hydrogen bond begins with the homolytic stretchin g of the C-H bond and then becomes a heterolytic dissociation, the tra nsition state appearing very near the region of the crossing between b oth 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.