Density Functional Study of Addition of Fluoromethyl Radicals to Fluoroethylenes: Estimation of Activation Energies

The addition reactions of �ECH₃, �ECH₂F, �ECHF₂, and �ECF₃ radicals to ethylene, monofluoroethylene, difluoro-ethylene, trifluoroethylene, and tetrafluoroethylene have been investigated using density functional theory (DFT, Kohn-Sham scheme) and Hartree-Fock (HF) methods. In the DFT calculations, we have used both pure and hybrid (partly including HF) exchange and Lee/Yang/Parr or Perdew/Wang 91 correlation functionals with the 6-31G* basis set. The same basis was taken in the HF calculations. For all possible combinations of fluorosubstituted methyl radicals and ethylenes, structures of reactants and transition states have been located. Inclusion of electron correlation was shown to be important in reproducing experimental activation barriers, though the results were strongly dependent on the type of functionals. The Becke's three-parameter hybrid with Perdew/Wang 91 gradient-corrected correlation functional B3PW91 gave the best estimates of the activation energies.