Electron Transfer in Radicals

According to the pioneering work of Weller and coworkers, back electron transfer in radical ion pairs can proceed by two different mechanisms [53 a], Le. a slow homogeneous recombination (second order) and a fast geminate recombination (first order). Both may lead to triplets of either the donor or the acceptor, depending on the energetics. 

L. T. Calcaterra, G. L. Closs, and J. R. Miller, Fast intramolecular electron transfer in radical ions over long distances across rigid saturated hydrocarbon spacers,. Am. Chem. Soc. 105 670-671 (1983). 

Cossy J (2001) Photoinduced electron transfer in radical reactions. In Renaud P,... 

The occurrence of intramolecular electron transfer in radical ion bond cleavage reactions is probably not straightforward and in this respect, two examples may help the reader—C-H deprotonation in the toluene radical cation and C-Cl bond cleavage in the 4-nitrobenzyl chloride radical anion (Scheme 25). 

Roth, H. D., Return Electron Transfer in Radical Ion Pairs of Triplet Multiplicity, Pure Appl. Chem. 2005, 77, 1075 1085. 

Miller, J. R., Calcaterra, L. T., Closs, G. L., Intramolecular Long distance Electron Transfer in Radical Anions. The Effect of Free Energy and Solvent on the Reaction Rates, J. Am. Chem. Soc., 1984, 106, 3047 3049. 

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