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羧酸酯的亲核取代反应速率受羧酸酯的离去基团(LG)、非离去基团(NLG)和亲核试剂(Nu)结构的影响.从文献整理了大量结构多样的羧酸酯与各种亲核试剂发生亲核取代反应的表观二级速率常数kN,基于亲核取代反应机理,用非离去基团的极化效应指数PEI(NLG)和基团体积参数GVI(NLG),亲核试剂与离去基团的体积参数之比GVI(Nu)/GVI(LG),以及亲核试剂与离去基团共轭酸的p Ka之差(p Ka(Nu)-p Ka(LG))分别表征非离去基团、离去基团和亲核试剂的结构特征及亲核试剂与离去基团的相互竞争,并用上述参数对73组亲核取代反应的logkN建立多元线性回归模型,得到较好的结果.该模型所用参数简便,物理意义明确,为从分子结构特征定量估算羧酸酯亲核取代反应的速率提供了理论依据.
The nucleophilic substitution reaction rate of carboxylic acid esters is affected by the structures of the leaving groups (LG), non-leaving groups (NLG) and nucleophiles (Nu) of carboxylic acid esters.A large number of structurally diverse carboxylic acids The apparent second-order rate constants, kN, of nucleophilic substitution reactions of various nucleophiles with various nucleophiles were investigated by the mechanism of nucleophilic substitution reaction. The polarization index PEI (NLG) of non-leaving groups and the group volume parameter GVI ( NLG), the ratio of the volumetric parameter of the nucleophile to the leaving group, GVI (Nu) / GVI (LG), and the difference between the pKa of the conjugate acid of the nucleophile and the leaving group p Ka (LG)) were used to characterize the structural characteristics of non-leaving groups, leaving groups and nucleophiles and competition between nucleophiles and leaving groups, respectively. The logkN of 73 groups of nucleophilic substitution reactions were established by the above parameters Multivariate linear regression model and good results.The parameters used in this model are simple and have clear physical meaning, which provides a theoretical basis for the quantitative estimation of the rate of nucleophilic substitution reaction of carboxylic acid esters from the molecular structural features.