Abinitio theoretical studies of the reactions between fluorine atoms and halomethanes of type CHCl3- xFx ( x=0, 1, 2 or 3)

Abstract

Ab initio calculations were performed on the series of H-abstraction reactions from halomethanes of CHCl_3-xF_x by fluorine atom attack. The characteristics (geometry, energy, frequencies) of reactants, transition states and products were determined at different levels of theory from Hartree–Fock to the correlated second order Møller–Plesset level MP2 with basis sets of increasing size [6-31G(d), 6-311G(d,p) and 6-311G(2d,2p)]. Conventional transition state theory and tunneling corrections were used to predict rate constants at room temperature. It is shown that only large basis sets including polarisation functions and correlated energy calculations can predict thermodynamic and kinetic parameters in good agreement with experimental data. The more reliable results are obtained if the energies and the optimised geometries are calculated at the same level or at a level where the addition of more basis functions will not change the geometries. Reactivity trends along the series of studied reactions were inspected and discussed in terms of chlorine and fluorine substitutions.