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On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. I

Marcus, R. A. (1956) On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. I. Journal of Chemical Physics, 24 (5). pp. 966-978. ISSN 0021-9606. doi:10.1063/1.1742723.

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A mechanism for electron transfer reactions is described, in which there is very little spatial overlap of the electronic orbitals of the two reacting molecules in the activated complex. Assuming such a mechanism, a quantitative theory of the rates of oxidation‐reduction reactions involving electron transfer in solution is presented. The assumption of "slight‐overlap" is shown to lead to a reaction path which involves an intermediate state X* in which the electrical polarization of the solvent does not have the usual value appropriate for the given ionic charges (i.e., it does not have an equilibrium value). Using an equation developed elsewhere for the electrostatic free energy of nonequilibrium states, the free energy of all possible intermediate states is calculated. The characteristics of the most probable state are then determined with the aid of the calculus of variations by minimizing its free energy subject to certain restraints. A simple expression for the electrostatic contribution to the free energy of formation of the intermediate state from the reactants, ΔF*, is thereby obtained in terms of known quantities, such as ionic radii, charges, and the standard free energy of reaction. This intermediate state X* can either disappear to reform the reactants, or by an electronic jump mechanism to form a state X in which the ions are characteristic of the products. When the latter process is more probable than the former, the over‐all reaction rate is shown to be simply the rate of formation of the intermediate state, namely the collision number in solution multiplied by exp(—ΔF*/kT). Evidence in favor of this is cited. In a detailed quantitative comparison, given elsewhere, with the kinetic data, no arbitrary parameters are needed to obtain reasonable agreement of calculated and experimental results.

Item Type:Article
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Marcus, R. A.0000-0001-6547-1469
Additional Information:© 1956 American Institute of Physics. Received July 28, 1955. This research was supported in part by the Office of Naval Research under Contract No. Nonr839(09). Reproduction in whole or in part is permitted for any purpose of the U. S. Government.
Funding AgencyGrant Number
Office of Naval Research (ONR)Nonr 839(09)
Subject Keywords:Free energy; Chemical reaction theory; Electron transfer; Transfer reactions; Electrostatics
Issue or Number:5
Record Number:CaltechAUTHORS:20140505-162124775
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Official Citation:Marcus, R. A. (1956). On the Theory of Oxidation‐Reduction Reactions Involving Electron Transfer. I. The Journal of Chemical Physics, 24(5), 966-978. doi: doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45509
Deposited On:06 May 2014 16:20
Last Modified:10 Nov 2021 17:04

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