KINETICS AND MECHANISM OF REACTIONS OF BENZHYDRYL CHLORIDES WITH ANILINES

Nucleophilic substitution reactions of substituted benzhydryl chlorides with anilines in acetonitrile and methanol are investigated. The reactions are found to proceed by the attack of nucleophile on the preformed carbocation, I, within the ion pair. The cross-interaction constants, rho(XY), are relatively large in both acetonitrile (rho(X)Y = -2.47) and methanol (rho(XY) = -1.46). The isokinetic points (sigma(Y)(+)) where rho(X) (rho(nuc)) is zero and the sign of rho(X) changes, are observed at positive substrate substituent constants, sigma(Y)(+) = 0.13 and 0.22 in acetonitrile and methanol, respectively. The isokinetic phenomenon (rho(X) = 0) has been shown to occur when the thermodynamic driving force, Delta G degrees, is practically completely compensated for by the intrinsic barrier, Delta G(0)(double dagger). The two change in a compensatory manner; the intrinsic barrier becomes higher when resonance electron delocalization of the Y substituent to C-alpha is stronger, which in turn results when the thermodynamic driving force becomes higher by stronger electron-withdrawing alpha-substituents, R(1) and/or R(2).