Some comments on valence bond representations for the radical exchange reaction X*+R:Y-->X:R+Y*

Qualitative valence bond formulations by Hiberty and co-workers (Hiberty, P. C.; Megret, C.; Song, L.; Wu, W.; Shaik, S. J. Am. Chem. Soc. 2006, 128, 2836) of mechanisms for the radical exchange reactions H*+F:H-->H:F+H* and F*+H:F-->F:H+F* are compared to a previously published formulation of the generalized radical exchange reaction X*+R:Y-->X:R+Y*. The former formulation uses covalent-ionic VB complexes, and the latter formulation, which is more general, involves the formation of reactant-like and product-like complexes at intermediate stages along the reaction coordinate.