Reinterpretation of Curved Hammett Plots in Reaction of Nucleophiles with Aryl Benzoates: Change in Rate-Determining Step or Mechanism versus Ground-State Stabilization
作者:Ik-Hwan Um、Hyun-Joo Han、Jung-Ae Ahn、Swan Kang、Erwin Buncel
DOI:10.1021/jo026339g
日期:2002.11.1
A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N 3 - with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O - 20 mol % dimethyl sulfoxide at 25.0 degrees C. Hammett log k vs sigma plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving
动力学研究表明,阴离子亲核试剂OH-,CN-和N 3-与苯甲酰基以及芳氧基部分上具有取代基的苯甲酸芳基酯在25.0的H2O-20 mol%的二甲亚砜中反应这些系统的Hammett log k vs sigma图始终是非线性的。但是,考虑了一种可能的传统解释,该解释涉及速率确定步骤的变化导致具有曲率的四面体中间体的机理,但被拒绝了。提出的解释涉及通过两阶段机理中的苯甲酰基取代基和亲电子羰基中心之间的共振相互作用实现基态稳定。因此,基于Yukawa-Tsuno方程很好地容纳了数据,该方程给出了所有三种亲核试剂的线性图。