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

Ab initio calculations were performed on the series of II-abstraction react ions from halomethanes of CHCl3-xFx by fluorine atom attack. The characteri stics (geometry, energy, frequencies) of reactants, transition states and p roducts were determined at different levels of theory from Hartree-Fock to the correlated second order Moller-Plesset level MP2 with basis sets of inc reasing size [6-31G(d), 6-311G(d,p) and 6-311G(2d,2p)]. Conventional transi tion state theory and tunneling corrections were used to predict rate const ants at room temperature. It is shown that only large basis sets including polarisation functions and correlated energy calculations can predict therm odynamic and kinetic parameters in good agreement with experimental data. T he more reliable results are obtained if the energies and the optimised geo metries are calculated at the same level or at a level where the addition o f more basis functions will not change the geometries. Reactivity trends al ong the series of studied reactions were inspected and discussed in terms o f chlorine and fluorine substitutions.