Dynamical barrier and isotope effects in the simplest substitution reaction via Walden inversion mechanism.
Dynamical barrier and isotope effects in the simplest substitution reaction via Walden inversion mechanism.
复制标题
通过瓦尔登反转机制实现最简单取代反应中的动态势垒和同位素效应
DOI：
10.1038/ncomms14506
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发表时间：
2017-02-22
影响因子：
16.6
通讯作者：
Zhang DH
中科院分区：
文献类型：
--
作者：
Zhao Z;Zhang Z;Liu S;Zhang DH
通过瓦尔登转化机制在碳原子上发生的反应是化学中最重要和最有用的一类反应。在这里，我们报告一个准确的理论研究的最简单的反应类型：H+ CH 4取代反应及其同位素类似物。结果发现，反应阈值与碰撞能量是相当高的势垒高度。该反应表现出强烈的正常二级同位素效应的截面上测得的反应阈值以上，和一个小的，但反向的二级动力学同位素效应在室温下。详细的分析表明，反应进行沿着路径具有较高的势垒高度，而不是最低能量的路径，因为伞角的非反应甲基不能改变同步与其他反应坐标在反应过程中，由于不充分的能量转移从平移运动到伞模式。
Reactions occurring at a carbon atom through the Walden inversion mechanism are one of the most important and useful classes of reactions in chemistry. Here we report an accurate theoretical study of the simplest reaction of that type: the H+CH4substitution reaction and its isotope analogues. It is found that the reaction threshold versus collision energy is considerably higher than the barrier height. The reaction exhibits a strong normal secondary isotope effect on the cross-sections measured above the reaction threshold, and a small but reverse secondary kinetic isotope effect at room temperature. Detailed analysis reveals that the reaction proceeds along a path with a higher barrier height instead of the minimum-energy path because the umbrella angle of the non-reacting methyl group cannot change synchronously with the other reaction coordinates during the reaction due to insufficient energy transfer from the translational motion to the umbrella mode.