醇酸热消除反应的理论研究

THEORETICAL STUDIES ON THE MECHANISM OF THE α-HYDROXY-ACID GAS-PHASE ELIMINATION PROCE

采用AMI半经验分子轨道方法，辅以Berny梯度优化方法，对醇酸（即α一羟基酸）在气相中的热消除反应进行了研究．计算与实验结果对比得到如下结论：（1）反应是2步过程，通过2个过渡态和1个中间体得到产物．第1步通过1个五元环过渡态，第2步通过1个三元环过渡态．（2）该反应的取代基效应表明，烷基的斥电子效应有利于醇酸的热消除过程，取代基的加入有利于反应的进行．

The α- hydroxy- acid gas - phase eilmination process is studied by semiempirical molecular orbital AM1 method and Berny energy gradient technique. The calculated results can be summed up as follows: (1) The elimination process is a stepwise reaction.In the first step, α 3 -membered ring intermediate is formed via a 5-membered ring transition;While the product is formed in the second step via a 3 -membered ring transition state. (2) The obtained results of the substituent effect show that the increase of electronic transmission of the alkyl groups is favorable for the reaction. Other substituents(eg. - Cl, - CH= CH2) are also favourable for this process.