AN MCSCF/MP2 STUDY OF METHYLENE INSERTION-ABSTRACTION REACTIONS WITH C-H AND C-CL BONDS

The reaction of singlet and triplet methylene with H3CCl has been investigated using ab initio MCSCF and multi-reference MP2 methods (MCSCF/MP2) with a 6-31G* basis set. In both singlet and triplet cases two transition states (one for the C-H and one for the C-Cl attack) have been located. For the triplet state the two transition structures correspond to H and Cl abstraction, respectively, with the H abstraction favoured at the MCSCF/MP2 level. For the singlet state the transition structures do not allow the type of path followed by the reaction to be assessed. The problem has been solved by computing the intrinsic reaction coordinate (IRC). The IRC results have demonstrated that the two transition states correspond to a methylene insertion into the C-H bond and to a Cl abstraction. The Cl abstraction is favoured with respect to the C-H insertion at the MCSCF/MP2 level in agreement with the experimental evidences. A qualitative diabatic analysis has been used to rationalize these results.