Reaction of (E)-O-Arylbenzaldoximes with Sodium Methoxide in Methanol. Effect of Leaving Group upon Nitrile-Forming Transition State

Reactions of (E)-O-arylbenzaldoximes 1-3 with MeONa-MeOH have been studied kinetically. The reactions proceed via competing E2 and S_NAr reactions, in which the first step is rate-determining. Although the reactions were strongly influenced by the electronic effect of the β-and O-aryl substituents, they were insensitive to the steric effect of the O-aryl group, except that the SNAr reaction was retarded by the CF₃ group of 2. For eliminations from 1-3 promoted by MeONa-MeOH, the k_H/k_D value increased and the Hammett ρ value decreased with better leaving groups. From these results, the effect of leaving group variation upon the nitrile-forming transition state is assessed.