ABINITIO STUDY OF THE INSERTION REACTION OF MG INTO THE CARBON HALOGEN BOND OF FLUOROMETHANE AND CHLOROMETHANE

Theoretical calcuations using self-consistent field (SCF) and Moller-Plessett perturbation theory, up to fourth order (MP4), have been carried out on the gas-phase Mg + CH3X --> CH3MgX Grignard reaction surface for X = F and Cl. The transition-state energies, geometries, and vibrational frequencies for both reactions are presented and compared to the smaller Mg + HX --> HMgX reaction. The transition states for both X = F and X = Cl are found to possess C(s) symmetry and to be almost identical in structure. The activation energy for the Mg + fluoromethane reaction is found to be 31.2 kcal.mol-1, while that for the chloromethane reaction is substantially higher, at 39.4 kcal.mol-1, calculated at the MP4SDTQ level by using the 6-311G(d,p) basis. The intrinsic reaction coordinate has been followed down from the transition state toward both reactants and product for the Mg + CH3F --> CH3MgF reaction, confirming the connection of these points on the potential surface.