Marcus Theory Applied to Electron Transfer

Without a doubt, the discipline where Marcus theory has had the most impact is in the study of electron transfer, both in chemistry and biology. Electron transfers are ubiquitous in chemistry, being involved in electrochemistry, redox reactions, many enzymatic reactions, and photosynthesis. Furthermore, many classic organic reactions have now been shown to have an electron-transfer component (see SET reactions in Chapter 11 and exciplexes in Chapter 16). 

In the calculation of rate constants for electron transfers, the Marcus equation takes a slightly different form than given in Eq. 7.63. As shown in Eq. 7.65, there is still a quadratic dependence upon the free energy change for the reaction, but now there is a new term, 2, which is a value that reflects the required reorganization energy. This term takes into account the rearrangement of the system of reactants and solvents discussed above that are neces- 

Reorganization energy X is the difference in energy between donor and acceptor orbitais that must be achieved by molecuiar distortions and/or solvent reorganization so that the orbitals become equal in energy 

Miller, J. R, Calcaterra, L. T., and Closs, G. L. Intramolecular Long-Distance Electron Transfer in Radical Anions. The Effects of Free Energy and Solvent on the Reaction Rates. /. Am. Chem. Soc., 106,3047 (1984). Closs, G. L., and Miller, J. R. Intramolecular Long-Distance Electron Transfer in Organic Molecules. Science, 240,440 (1988). 

Electron-transfer reaction used to uncover the inverted region 

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