SN1-SN2 and SN2-SN3 mechanistic changes revealed by transition states of the hydrolyses of benzyl chlorides and benzenesulfonyl chlorides

• Published in: Journal of Computational Chemistry Vol. 35; no. 15; pp. 1140 - 1148
• Main Authors: Yamabe, Shinichi, Zeng, Guixiang, Guan, Wei, Sakaki, Shigeyoshi
• Format: Journal Article
• Language: English; Japanese
• Published: Blackwell Publishing Ltd 05.05.2014; Wiley
• Subjects: benzenesulfonyl and benzyl chlorides; hydrolysis; nucleophilic substitutions; SN1-SN2; SN2-SN3; theoretical calculation
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.23607

Hydrolysis reactions of benzyl chlorides and benzenesulfonyl chlorides were theoretically investigated with the density functional theory method, where the water molecules are explicitly considered. For the hydrolysis of benzyl chlorides (para‐ZC6H4CH2Cl), the number of water molecules (n) slightly influences the transition‐state (TS) structure. However, the para‐substituent (Z) of the phenyl group significantly changes the reaction process from the stepwise (SN1) to the concerted (SN2) pathway when it changes from the typical electron‐donating group (EDG) to the typical electron‐withdrawing one (EWG). The EDG stabilizes the carbocation (MeOC6H4CH2+), which in turn makes the SN1 mechanism more favorable and vice versa. For the hydrolysis of benzenesulfonyl chlorides (para‐ZC6H4SO2Cl), both the Z group and n influence the TS structure. For the combination of the large n value (n > 9) and EDG, the SN2 mechanism was preferred. Conversely, for the combination of the small n value and EWG, the SN3 one was more favorable. © 2014 Wiley Periodicals, Inc. Transition states of hydrolysis reactions ZC6H4XCl are investigated with specific water molecules (n = 6, 9, 11, 17, 23, and 29), where X = CH2, and SO2 and Z = O2N, Cl, H, H3C, and H3CO. In the case of a large n value and an electron‐donating Z group, the hydrolysis reaction occurs through a SN2 mechanism. However, the combination of a small n value and an electron‐withdrawing Z group converts the reaction mechanism to SN3.