The theory of electron transfer processes

Of more direct interest to kineticists is a reconsideration by Marcus and Sutin of the basis for the well known equation (1) relating activation free energies AG to 

However, equation (2) also predicts that as AG becomes more negative a decreases, until when AG —4 4 further decrease in AG leads to an increase in AG. Marcus 

The minimum value of AG (on the old theory) or the limiting value (on the new) is expected to be zero only if the work terms are negligible, and if there are no rapid 

The limiting value, AG kcalmol S had previously been felt to be rather high, and one possible explanation considered was a rapid equilibrium between the two spin states of cobalt(m) tlg t ge prior to the electron transfer. The data from other oxidants have weakened if not altogether removed the necessity for this. It has moreover been argued from ligand-field considerations that for the hexa-aquo-cobalt(iii) ion the spin-change free energy may in any case be quite small.  

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The above examples illustrate the important types of solution reactions, especially from the point of view of analytical chemistry. But it is not an exhaustive list. For example, another type of solution reaction which is of interest to theorists is the isomerization reaction [G3]. In this chapter, the theory of the electron transfer process is considered in detail. Some of the results from this treatment can also be applied to other bimolecular processes. More details follow in the later sections of this chapter. 

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