Nucleophilic substitution reaction of 1-phenylethyl chlorides in methanol

Abstract

Nucleophilic substitution reactions of 1-(Y-phenyl)ethyl chlorides with X-anilines have been investigated in methanol at 65.0 °C. An isokinetic point is obtained at σ_Y⁺=ca.– 0.23 with ρ_x= 0; the sign of ρ_x changes at this point from positive for the relatively strong electron donating Y substituents to negative for the more electron withdrawing Y substituents.

The magnitude of the cross-interaction constant, ρ_xy, between the substituents X and Y is unusually large with the relatively small magnitude of ρ_x° resulting in an observable isokinetic point at σ_Y⁺=–ρ_x°//_ρxy=–0.23. These results are interpreted in terms of a transition state (TS) structure in which nearly complete bond formation between the nucleophile and cation formed in an ion-pair preequilibrium is coupled with a TS imbalance phenomenon. The results of kinetic isotope effect studies involving deuteriated anilines and methanol are also in line with this mechanism.