氧杂环丁烷热解机理的量子化学研究

本文利用半经验分子轨道理论研究了氧杂环丁烷热解为甲醛和乙烯的反应机理计算是采用半经验方法AM1进行的, 各种驻点全部运用Berny梯度方法优化. 同时, 对过渡态的结构进行了振动分析的确证. 计算表明: 1)不存在协同的同面-同面反应途径的过渡态, 其驻点只是一个二级鞍点; 2) 协同的同面-异面反应途径需要经过一个能量很高的过渡态; 3)有利的反应途径是包含了双自由基中间体的分步过程。

Quantum Chemical Studies on the Thermolysis of Oxetane

The mechanism of the thermolysis of oxetane to form ethylene and formaldehyde has been studied in detail by semiempirical molecular orbital theory. The calculations have been carried out using a new general purpose quantum mechanical molecular model AM_1 presented by M. J. S. Dewar et al in 1985,and performed with GAUSSIAN 86 program. The various critical points in the region of the reaction have been fully optimized with Berny gradients and transition structures (TS) have been confirmed by frequency analysis. By calculations, we concluded that: 1) concerted supra-supra reaction path doesn't exist and the critical point involved is a second-order asddle point with two negative eigenvalues; 2) concerted supra-antara approach is found to proceed via a very high energy transition state; 3) the favoured reaction pathway is found to proceed via a stepwise approach characterized by diradical intermediates. The stepwise approach has two different pathways, one of them is to cleava carbon-car-bon bond firstly and then carbon-oxygen bond, it involves gauche intermediate and corresponding transition states. Another stepwise pathway is to break carbon-oxygen bond at first and then carbon-carbon bond, it proceeds vis a gauche or a trans intermediate and corresponding transition states. The two stepwise pathways coexist and compete each other.