Ab-initio mechanistic studies of radical reactions. Directive effects in the addition of methyl radical to unsymmetrical fluoroethenes

Abstract

Addition of methyl radical to unsymmetrical fluoroethenes has been studied by ab-initio molecular orbital calculations. In agreement with experimental data, we find that the reaction rate decreases in going from ethene to mono- and 1,1 di-fluoroethene, but sharply increases in the case of trifluoroethene. Additions to the more fluorinated carbon atoms are always thermodynamically favoured, but addition to the CH₂ end of mono- and 1,1 di-fluoroethene is kinetically favoured. The general trends of the potential energy barriers have been rationalized by means of the energy decomposition scheme proposed by Morokuma. Non potential energy effects have also been considered, but their role is negligible.