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Theory of Rates of S_N2 Reactions and Relation to Those of Outer Sphere Bond Rupture Electron Transfers

Marcus, R. A. (1997) Theory of Rates of S_N2 Reactions and Relation to Those of Outer Sphere Bond Rupture Electron Transfers. Journal of Physical Chemistry A, 101 (22). pp. 4072-4087. ISSN 1089-5639. doi:10.1021/jp963722e.

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A model is considered for S_N2 reactions, based on two interacting states. Relevant bond energies, standard electrode potentials, solvent contributions (nonequilibrium polarization), and steric effects are included. A unified approach is introduced in which there can be a flux density for crossing the transition state, which is either bimodal, one part leading to S_N2 and the other to ET products, or unimodal with a less marked energy-dependent separation of the rates of formation of these products. In a unified description an expression is given for the reorganization energy, which reduces in the appropriate limits to the pure S_N2 and ET/bond rupture cases. Expressions are obtained for the S_N2 rate constant and for its relation to that of the concerted electron transfer/bond rupture reaction. Applications of the theory are made to the cross-relation between rate constants of cross and identity reactions, experimental entropies and energies of activation, the relative rates of S_N2 and ET reactions, and the possible expediting of an outer sphere ET reaction by an incipient S_N2-type interaction. Results on the photoelectron emission threshold energies of ions in solution provide some information on a solvation term, and another quantity can be estimated using data from gas phase S_N2 reactions or from quantum chemistry calculations. Also introduced for comparison is an adiabatic model that is an extension of a bond energy−bond order formulation for gas phase reactions.

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Marcus, R. A.0000-0001-6547-1469
Additional Information:© 1997 American Chemical Society. Received: November 7, 1996; In Final Form: February 26, 1997. It is a pleasure to acknowledge the support of this research by the National Science Foundation and the Office of Naval Research. The author has benefitted considerably from an extensive correspondence with Jean-Michel Savéant. I am also particularly indebted to John Brauman, Henning Lund, Sason Shaik, and Lennart Eberson for their helpful comments.
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Office of Naval Research (ONR)UNSPECIFIED
Issue or Number:22
Record Number:CaltechAUTHORS:20150519-085740363
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Official Citation:Theory of Rates of SN2 Reactions and Relation to Those of Outer Sphere Bond Rupture Electron Transfers R. A. Marcus The Journal of Physical Chemistry A 1997 101 (22), 4072-4087 DOI: 10.1021/jp963722e
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57635
Deposited By: Tony Diaz
Deposited On:19 May 2015 16:08
Last Modified:10 Nov 2021 21:52

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