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

Article abstract of DOI:10.1021/ja00321a011

The Bronsted α (=d(lnk_ij)/d(lnK_ij)) for an atom- or group-transfer reaction depends on the location of the substitution and the tightness of the transition state (τ) as well as the resemblence of the transition state to reactants and products.Within Marcus theory, τ can be related to rates of symmetrical reactions.These ideas have been successfully applied to hydride transfer between NAD⁺ analogues.A series of 1-benzyl-3-cyanoquinolinium ions, substituted in the benzyl group, has been prepared.Rate and equilibrium constants have been determined for their reactions with 10-methylacridan.A Bronsted α of 0.37 has been obtained.From Marcus theory, using previously reported symmetrical exchange rate constants, the same value is calculated.This is displaced from 0.5 mainly by the looseness of the transition state, a perpendicular effect related to the partially hydridic character of the in-flight H.This H is estimated to have -0.23 electron of excess charge and a total bond order of 0.77 in the transition state.