Methyl Transfer Reaction IX. Linear Free Energy Relations and the Reactivity—Selectivity Principle

Abstract

Methyl transfers between nucleophiles are representative and uncomplicated examples of group transfer reactions. Data are shown for rates and equilibria sufficient to allow a nearly rigorous application of the Marcus equation. Selectivities with a series of nucleophiles do not vary significantly with reactivity over a wide range of reactivities, except for diffusion controlled reactions. The Marcus equation, for which the necessary data are now available to calculate the rate, fits very well in cases to which it has been applied. It is shown that the (quadratic) Marcus equation is expected to be compatible with experimental linear free energy relations for most reactions; generally only very fast reactions will reveal the curvature, thus the Hammond postulate, the reactivity—selectivity principle, the variable transition state and the Marcus equation are not incompatible with linear free energy relations.