Valence bond Modeling of barriers in the nonidentity hydrogen abstraction reactions, X 'center dot+H-X -> X '-H+X center dot (X ' not equal X = CH3, SiH3, GeH3, SnH3, PbH3)
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Breathing orbital valence bond (BOVB) computations (Hiberty, P. C.; Humbel, S.; Byrman, C. P.; van Lenthe, J. H. J. Chem. Phys. 1994, 101, 5969) are used to obtain nonidentity barriers for hydrogen transfer reactions between X and X' groups, X not equal X' = CH3, SiH3, GeH3, SnH3, PbH3. Modeling of these barriers by means of VB state correlation diagrams (Shaik, S.; Shurki, A. Angew. Chem., Int. Ed. Engl. 1999, 38, 586) leads to a simple expression for the barrier (eq 29) as an interplay of an intrinsic term and the reaction driving force. The equation predicts barrier heights that are compatible with the BOVB computed barrier heights. Its comparison with the Marcus equation shows similarities and differences.