Theoretical study of the kinetics of hydrogen abstraction in reactions of simple hydrogen compounds with triplet difluorocarbene

The stationary points of H-atom abstraction reactions of triplet CF2 (B-3(1)) with XHn (n = 1-4: X = H, F, Cl, Br, O, S, N, P, C and Si) were computed using UCCSD(T) methods with 6-311++G(3df,2p) and aug-cc-pVTZ basis sets. Covalent surface crossing heights, calculated using the X-H and C-H bond dissociation energies of XHn and of the CHF2 product, correlate well with the computed classical barrier heights. Within each group of co-reactants, the barrier heights increase with increasing X-H bond dissociation energy, whereas the C-H bond lengths of the transition structures decrease. H-abstractions remain energy-demanding processes for second-row X atoms, but become more facile for their third-row X counterparts. (C) 2004 Elsevier B.V. All rights reserved.