正碳离子氢原子移位重排反应研究

Studies on rearranging reaction of carbon cation through hydrogen atom shift

正碳离子是重要的有机化学反应中间产物,而氢原子移位则是正碳离子异构化的主要反应途径。本文利用量子化学方法对丙基伯正碳离子和仲正碳离子的结构和生成热进行了研究,优化了丙基伯正碳离子和仲正碳离子的结构,计算得到了这两种正碳离子的能量。结果表明,丙基伯正碳离子的生成热为214.4kcal/mol,丙基仲正碳离子的生成热为197.3kcal/mol,伯正碳离子的生成热比仲正碳离子的生成热高17.1kcal/mol,表明丙基伯正碳离子能够通过氢原子移位转变为丙基仲正碳离子。以丙基伯正碳离子和仲正碳离子的结构为起点进行过渡态搜索,得到了丙基伯正碳离子通过氢原子移位转化为丙基仲正碳离子,从而进行正碳离子重排反应的过渡态,并通过振动方式分析,对过渡态进行了确认。计算得到的丙基正碳离子通过氢原子移位进行重排反应的能垒为3.5kcal/mol,表明丙基伯正碳离子很容易转化为仲正碳离子。

Carbon cations are important organic reaction intermediates, and hydrogen shift is a key path through which carbon cations isomerizes. In this paper, quantum mechanical methods were used to study the structure of primary and secondary propyl cation. It was found that heat of formation of primary propyl cation was 17. 1 kcal/mol higher than that of secondary propyl cation, which meant that primary propyl cation could transform into secondary propyl through hydrogen atom shift. Based on the structures of primary and secondary propyl cation, transition state had been found. Energy barrier of the reaction was 3. 5 kcal/mol, which showed that the reaction could take place easily.