Theoretical Studies on the Design and Control of Pricyclic Reactions

我们研究了以下项目：(1)芳香性的新定义及其应用：在从头算分子轨道方法建立的CiLC分析的基础上，提出了环状π共轭化合物芳香性的新判据。新标准规定所有键应具有等效的电子结构，并且单重态耦合项和极化项的权重之间的差异应较小。(2)Diels-Alder反应机理：采用CASSCF分子轨道方法研究了丁二烯与甲醛和硫代甲醛的杂Diels-Alder反应的协同和逐步机理。两个系统的协同路径比逐步路径更有利。还研究了丁二烯与乙烯之间的Diels-Alder反应的协同和逐步机理的取代效应。(3)1,3-偶极环加成机理：反应机理可分为两类：离子电环和双自由基偶联机理。离子电环机制发生在亲偶极体的两个原子之间电负性差异较大的反应体系中，并且它们的原子与1,3-偶极子中带有相反电荷的原子发生反应。双自由基耦合机制通过两个过程发生：第一个过程是一个电子从1,3-偶极子的边缘原子向中心原子运动，从而形成双自由基态。(4)Cope重排反应机理：研究了1,5-己二烯及其单苯基和二苯基衍生物反应中Cope重排的机理。对1,5-己二烯反应中C_2h>切割的势能面进行了CiLC分析，给出了芳香族过渡态、双自由基中间体以及它们之间的过渡态的典型电子特征。

We studied the following projects.(1)New Definition of Aromaticity and the Applications : A new criterion of aromaticity for cyclic π-conjugated compounds is proposed on the basis of CiLC analysis founded on ab initio molecular orbital methods. The new criterion states that the all bonds should have equivalent electronic structures and the difference between weights for the singlet coupling and polarization terms should be small.(2)Diels-Alder Reaction Mechanisms : The concerted and stepwise mechanisms of the hetero-Diels-Alder reaction of butadiene with formaldehyde and thioformaldehyde were studied by a CASSCF molecular orbital method. The concerted pathways for both systems are more favorable than the stepwise pathways. Substitution effects for concerted and stepwise mechanisms of the Diels-Alder reaction between butadiene and ethylene were also studied.(3)1,3-Dipolar Cycloaddition Mechanisms : The reaction mechanisms can be calssifled into two classes : ionic electrocyclic and diradical coupling mechanisms. Ionic electrocyclic mechanism occurs in reaction systems with a large difference in electronegativies between the two atoms of the dipolarophile and their atoms react with the atoms with each opposite charge of a 1,3-dipole. Diradical coupling mechanism occurs through two process : the first process is a one-electron movement from the edge atom to the center atom of a 1,3-dipole, which leads to a biradical state.(4)Cope Rearrangement Reaction Methanisms : The mechanism of the Cope rearrangement in the reaction of 1,5-hexadiene and its monophenyl and diphenyl deviatives was studied. CiLC analysis was performed for the potential energy surface of the C_<2h> cut in the reaction of 1,5-hexadiene, giving the typical electronic character for the aromatic transition state, diradical intermediate, and the transition state between them.