the leaving group in the RDS. Thus, the reactions have been concluded to proceed through a forced concerted mechanism with a highly unstable intermediate 7. Comparison of the current kinetic data with those reported previously for the corresponding reactions of Y‐substituted phenyl benzoates has revealed that modification of the nonleaving group from benzoyl to picolinyl causes not only an increase
用分光光度法测量了Y取代的苯基
吡啶甲酸(6a-6i)的碱
水解的二级速率常数(k OH –)。得到的线性Brønsted型图的βlg = -0.34,这是以前报道的通过逐步机理进行反应的典型反应,其中形成加成中间体是速率决定步骤(RDS)。但是,常数导致的Hammett相关性比常数差得多。此外,汤川-津野情节表现出与ρ优异的线性相关Ŷ = 0.82和- [R = 0.72,表明在RDS的离去基团的O原子上部分形成负电荷。因此,已经得出结论,反应是通过具有高度不稳定中间体7的强制协同机制进行的。将当前的动力学数据与以前报道的Y-取代
苯甲酸酯的相应反应进行的比较表明,从苯甲酰基到
吡啶甲酰基的非离开基的修饰不仅引起反应性的增加,而且引起反应机理的改变(即。 ,从逐步机制到强制一致的途径)。