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采用较新的半经验分子轨道方法Austin Model 1(简称AM1方法),辅以Berny梯度优化方法,对单线态氧(~1O_2)与咪唑的1,2-环加成反应,进行了理论研究。计算获得实验尚未检测到的4,5-二氧环丁烷(4,5-dioxetane)的结构,并在反应势能面上找到单重态双自由基中间体及通过该中间体的两步反应的过渡态。通过对过渡态的结构特征、虚振动方向以及对反应过程的电荷分布情况、轨道相互作用等的分析,说明该反应是经由单重态双自由基中间体的分步反应。两步反应的活化势垒分别为39.2kJ·mol~(-1)和150.5kJ·mol~(-1)。
The new semi-empirical molecular orbital method, Austin Model 1 (AM1) and the Berny gradient optimization method were used to study the 1,2-cycloaddition of singlet oxygen (~10) with imidazole. The structure of 4, 5-dioxetane, which has not been detected experimentally, was calculated and the singlet diradical intermediates and the two-step reaction through this intermediate were found on the reaction potential surface Transitional state. Through the analysis of the structural characteristics of the transition state, the direction of the virtual vibration and the charge distribution of the reaction process, the orbital interaction and so on, it is shown that the reaction is a stepwise reaction via the singlet diradical intermediate. The activation barriers of the two reactions were 39.2 kJ · mol -1 and 150.5 kJ · mol -1, respectively.