AbstractNovel mechanistic criteria forSNreactions were proposed on the relative magnitudes of ρZand interaction terms, ρijorPijvalues. The mechanistic change by the sign of the product of ρijs orPijs was also proposed. These criteria were applied to the reaction between substituted phenyl benzoates and amines and indicated that the sign of ρZis positive and the interaction termPXZis larger thanPYZ, hence these reactions proceed via anSANmechanism and a change in the substituent of the substrate leads to a change in the substituent of the substrate leads to a change in the transition state towards the Hammond eff