DENSITY-FUNCTIONAL STUDY OF ADDITION OF FLUOROMETHYL RADICALS TO FLUOROETHYLENES - ESTIMATION OF ACTIVATION-ENERGIES

The addition reactions of . CH3, . CH2F, . CHF2, and . CF3 radicals to ethylene, monofluoroethylene, difluoroethylene, trifluoroethylene, an d tetrafluoroethylene have been investigated using density functional theory (DFT, Kohn-Sham scheme) and Hartree-Fock (HF) methods. In the D FT calculations, we have used both pure and hybrid (partly including H F) exchange and Lee/Yang/Parr or Perdew/Wang 91 correlation functional s with the 6-31G basis set. The same basis was taken in the HF calcul ations. For all possible combinations of fluorosubstituted methyl radi cals and ethylenes, structures of reactants and transition states have been located. Inclusion of electron correlation was shown to be impor tant in reproducing experimental activation barriers, though the resul ts were strongly dependent on the type of functionals. The Becke's thr ee-parameter hybrid with Perdew/Wang 91 gradient-corrected correlation functional B3PW91 gave the best estimates of the activation energies.