Regioselectivity of methyl radical addition to fluoroethenes: a quantum mechanical study

The addition of the methyl radical to mono-, di- and tri-substituted alkenes has been studied by both post-Hartree–Fock and hybrid Hartree–Fock/density functional (B3LYP) methods. The B3LYP model confirms its reliability concerning activation energies and reaction enthalpies, but fails to reproduce the inversion of regioselectivity along the fluoroethene series. Only coupled cluster computations are completely reliable, but single-point computations at B3LYP geometries provide results close to those issuing from much more expensive coupled cluster geometry optimizations. The origin of regioselectivity trends is analysed in terms of spin densities and deformation energies.