摘要:
The kinetics of the reactions between 1-phenyl-2-propyl benzenesulfonates (PPB) and anilines in methanol at 65.0-degrees-C are investigated, and the mechanism is discussed on the basis of various selectivity parameters, especially on the cross-interaction constants, rho-ij. The aryl participation is significant only with the p-CH3O-substituted substrate. rho-XZ is positive, and accordingly the transition state (TS) variations with substituents are consistent with those predicted by the potential energy surface diagram. The TS is of an intermediate type between that for an associated (tight) and a dissociated (loose) S(N)2 process; it is rather tight, but bond breaking is ahead of bond making with positive charge development at the reaction center in the TS. The possibility of front-side attack with a four-center TS is precluded because of strong steric hinderance in a close approach of the two bulky groups, the nucleophile and leaving group, on the same side in the front-side attack.