Pyridinolysis of O,O-Diphenyl S-Phenyl Phosphorothiolates in Acetonitrile

Abstract

are biphasic concave downwards with breaks at Z = H. The large magnitudes of ρ X (ρ nuc), β X (ρ nuc), and the cross-interaction constant, ρ XZ, suggest frontside nucleophilic attack toward the leaving group. The sign reversal of ρ Z from positive in σ Z ≤ 0 to negative in σ Z ≥ 0 is interpreted as the change in mechanism from concerted to stepwise with rate-limiting expulsion of the leaving group. The anomalous negative sign of ρ Z for leaving groups with electron-withdrawing substituents is interpreted as the intramolecular ligand exchange process of the leaving group from the equatorial position in the intermediate to the apical position in the TS.