Thermodynamics electron transfer

As for the salt formation and single-electron transfer, thermodynamics for simple redox processes may be applied to predict their selectivity. As a first approximation, a cation with red lower and higher than 0.2 V would give a salt and a radical pair, respectively, when combined with [2 ]. In practice, the cations which were found to give salts with [2 ] have red values more negative than —0.8 V. On the other hand, quantitative single-electron transfer has been observed from [2 ] to the heptaphenyltropylium ion which is relatively unstable p/fR+ —0.54 in methanol (Battiste and Barton, 1968) and E ed —0.30 V vs. Ag/Ag in acetonitrile (Kitagawa et al., 1992). 

This represents electrodeless electrochemistry, whereby the only process is electron transfer and the only product is the one-electron adduct of 02, the superoxide ion (02). Through the use of redox mediator dyes and spectrophotometry, the electron-transfer thermodynamic reduction potential for 02 has been evaluated ... 

The need for quantitative bond energy data for oxygen-containing molecules in the condensed phase has prompted the development of an evaluation procedure that is based on electron-transfer thermodynamics. The approach is illustrated for H-O bonds and for Fe-0 bonds, but is applicable to any X-O bond for which appropriate electron-transfer potentials are available. Table 6(a) summarizes the one-electron standard reduction potentials for H3O+, HO-, HOH, O2, HOO-, 02 % -O-, and in aqueous solutions (see Table 1). 

If a catalyst (C) which can interact with one of the products of electron transfer (e.g., A in Scheme 2) is introduced into the D-A system, the factors to control the rate of electron transfer, AG°et and 2, may be altered. The AG°et value is shifted in the negative direction when the activation barrier of electron transfer is reduced to accelerate the rates of electron transfer as shown in Scheme 2, where C forms a complex with A. Since most organic compounds such as n acceptors in particular have small reorganization energies, the change of redox potentials due to the interaction of the corresponding radical anions with C may be the main factor to accelerate the rates of electron transfer. Thus, any catalyst C that can stabilize the products of electron transfer thermodynamically by complexation may act as an... 

Tsang, P.K.S. and D.T. Sawyer (1990). Electron-transfer thermodynamics and bonding for the superoxide (O ), dioxygen (O2), and hydroxyl (OH) adducts of (tetrakis(2,6-dichlorophenyl)porphinato)iron, manganese, and cobalt in dimethylfor-mamide. Inorg. Chem. 29, 2848-2855. 

Borgis D, Gendre L, Ramirez R Molecular density functional theory application to solvation and electron-transfer thermodynamics in polar solvents, J Phys Chem B... 

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