Separation thermodynamics and

As Bunnett has noted (4), the kinetic barrier to nucleophilic attack is affected by the thermodynamics of the reaction. If this thermodynamic contribution could be removed, then intrinsic nucleophilicities for substitution reactions could be obtained that would be independent of the leaving group. Pioneering work by Albery and Kreevoy (7), Pellerite and Brauman (8), and Lewis et al. (9) has shown that Marcus theory can be applied to methyl-transfer reactions to separate thermodynamic and kinetic contributions and provide intrinsic barriers to nucleophilic attack. One expression of Marcus theory is given in equation 1, where AE is the activation energy, AE° is the heat of reaction, and AE0 is the intrinsic activation energy or the barrier to reaction in the absence of any thermodynamic driving force. 

Ping-Pong mechanisms have separate thermodynamic and kinetic Haldanes for each half-reaction, and the overall Haldanes are the product of those for each half-reaction. Since one can combine two thermodynamic or two kinetic Haldanes, or one of each, there are four possible Haldanes for a Ping-Pong mechanism with two half-reactions, although only two of these will have V i/V 2 to the first power (the other two have this ratio to the second or zero power). 

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