Kinetics and Mechanism of Nucleophilic Displacement Reactions of Y-Substituted Phenyl Benzoates with Cyanide Ion

Bulletin of the Korean chemical society

Ik Hwan Um¹  Song I Kim¹  Eun Hee Kim¹ 

关键词: Aryl benzoates;    Br©ªnsted-type plot;    Hammett plot;    Rate-determining step;    Yukawa-Tsuno plot;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Second-order rate constants (kCN-) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-r) with CN- ion in 80 mol % H₂O/20 mol % DMSO at 25.0 �? 0.1 ^oC. The Br┆nsted-type plot is linear with �?_lg = -0.49, a typical �?_lg value for reactions reported to proceed through a concerted mechanism. Hammett plots correlated with �?^o and �?^- constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot for the same reaction exhibits excellent linearity with �?_Y = 1.37 and r = 0.34, indicating that a negative charge develops partially on the oxygen atom of the leaving aryloxide in the rate-determining step (RDS). Although two different mechanisms are plausible (i.e., a concerted mechanism and a stepwise pathway in which expulsion of the leaving group occurs at the RDS), the reaction has been concluded to proceed through a concerted mechanism on the basis of the magnitude of �?_lg and ヱY values.

【 授权许可】

Unknown