Number and Structure of Solvolysis Intermediates. IV. The Phenolysis of 1-(p-Tolyl)ethyl p-Nitrobenzoate: The Mechanism via a Single Stable Ion-Pair Intermediate with High Selectivity for Nucleophiles

Abstract

Abstract Optically active 1-(p-tolyl)ethyl p-nitrobenzoate (ROPNB) has been subjected to solvolysis in phenol where the solvolysis was previously found to proceed via a single stable ion-pair intermediate (Int-1) with high selectivity for nucleophiles, i.e., to exhibit the kinetic features expressed by the “B” pattern for the kp–kt profile. On the basis of the absolute configurations and the maximum rotations for the substrate and all of the products which have been chemically established, the stereochemical courses have been disclosed to be partial retention for ROPh formation (“retentive phenolysis”) and partial inversion for o- and p-RC6H4OH formation with predominant racemization in the solvolysis. These stereochemical outcomes indicate that the key intermediate (Int-1) which provides all of the products should have the structure of a carbocation ion pair shielded at the rear side by a phenol molecule (the rear-side shielded ion-pair intermediate) similarly to the key intermediates which are known for some other phenolysis systems. Consequently, the rear-side shielded ion-pair intermediate plays a key role regarding product formation in all retentive phenolysis systems.