[en] The aminolysis of thiophenyl cyclopentanecar-boxylates with benzylamines in acetonitrile proceeds by rate-limiting breakdown of a tetrahedral intermediate, T^±. The unusually large β_X (β_nuc) values can be accounted for by a strong localized cationic charge on the nitrogen atom of benzyl-amines in T^±, which is lost in the benzylamine expulsion from T^± (k_-a). The breakdown rate ratio of k_-a/k_b is large due to large k_-a and relatively small k_b. The proposed mechanism is also supported by a large positive cross-interaction constant, ρ_XZ (=1.72), adherence to the RSP, and low activation parameters. The greater than unity k_H/k_D values involving deuterated benzylamines suggests a four-center type hydrogen-bonded TS. The mechanisms of the aminolysis of aryl esters and carbonates, and their thiol, thiono and dithio derivatives have been extensively studied. Curved Bronsted plots in the aminolysis reactions have been interpreted in terms of a zwitterionic tetrahedral intermediate, T^±, in the reaction path and a change in the rate-limiting step from leaving group expulsion to attack by the nucleophile as the nucleophile becomes more basic. In some of the cases, however, the aminolysis has been found to proceed concertedly in a single step through a tetrahedral intermediate transition state (TS). The mechanistic change from a stepwise through an intermediate, T^±, to a concerted via a single TS has been reported to be caused by destabilization of the tetrahedral intermediate, T^±, due to several factors, e. g., an enhanced leaving ability of the leaving group (LG), strong electronic push provided by the substrate (nonleaving group) and destabilization rendered by the amines and by substitution of S^- by O^- in the tetrahedral intermediate, T^±

[en] We propose a concerted mechanism with a hydrogen bonded cyclic transition state for the aminolysis of aryl N,N-dimethyl thiocarbamates with benzylamines in acetonitrile based on the negative cross-interaction constant, failure of RSP, a strong push provided to expel ArS^- by the nonleaving group, Me₂N, the kinetic isotope effects greater than unity and relatively low ΔH^≠ with large negative ΔS^≠ values. Kinetic studies on the aminolysis mechanisms of aryl carbamates, are however relatively scarce, albeit they are structurally similar to the corresponding esters and carbonates. Recent works on the aminolysis of aryl thiocarbamates, with R = Et^4e and Ph^4d have indicated that the aminolysis rates with benzylamines in acetonitrile are more than 3 times faster with R = Et than with R = Ph in concerted processes. This rate enhancement with R = Et relative to R = Ph has been attributed mainly to a stronger push to expel the thiophenoxide leaving group by EtNH than by PhNH in the tetrahedral transition state. It is, however, not well understood that exactly what type of electronic effect is responsible for this push, e. g. is it a polar or a charge transfer effect? and whether there is a steric inhibition effect operative with a bulkier phenyl group relative to an ethyl group or not. In order to shed more light on the aminolysis mechanism of aryl N,N-dimethyl thiocarbamates by elucidating effects of the nonleaving (RNH) group in, we carried out kinetic studies on the aminolysis of aryl N,N-dimethyl thiocarbamates with benzylamines in acetonitrile, eq