Andreas Zavitsas - Whence the energy term of the rate constant?

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      Publication Details (including relevant citation   information):

     

        Journal of Physical Chemistry A 2010, 114, 5113-5118.     http://dx.doi.org/10.1021/jp101183w  

      Abstract:

     

        Insights into the causes of energy barriers to reactions are     obtained from our E* model for hydrogen     abstractions.Results of the model are in good agreement with     all eight experimentally studied symmetrical reactions of the     type X-H + •X -> X• + H-X. The E* energy is broken     down into three components: energy needed to overcome triplet     repulsion between the terminal Xs, energy needed to bring the     H-X bonds to their transition state distances, and energy gain     by the resonance stabilization of delocalization of the odd     electron over three atoms. The strength of the X-H bond is a     minor factor. The conclusion that triplet repulsion is a major     factor is supported by the London equation and by results of     recent high level theoretical calculations. The     E*model requires inputs of bond dissociation energies,     bond lengths, and infrared stretching frequencies of X-H and     X-X. Some reported failures of E* are shown to have     been caused by use of input values subsequently found to be     incorrect.  

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