Marcus Theory of a Parallel Effect on α for Hydride Transfer Reaction between NAD+ Analogues

Rate and equilibrium constants for hydride transfer from a series of 1,3-dimethyl-2-substituted phenylbenzimidazolines to a pyridinium ion, a quinolinium ion, and a phenanthridinium ion have been evaluated. Each oxidizing agent gives a linear Brønsted plot with slope, α. The α values vary systematically with the spontaniety of the reactions. They are in reasonable agreement with the predictions of modified Marcus theory. Their trend is very accurately predicted, showing a parallel (Leffler−Hammond) effect. These results make a multistep mechanism, involving high energy intermediates, very unlikely.