Wilsey S
Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK.
J Org Chem. 2000 Nov 17;65(23):7878-88. doi: 10.1021/jo0008946.
The triplet-state reactions of 1,4-pentadiene have been investigated using density functional theory (UB3LYP) and ab initio (CASSCF) calculations with a 6-31G basis set. Intramolecular [2 + 2] photocycloadditions and three different reaction pathways leading to vinylcyclopropane have been examined. The computed results are in good agreement with the experimental observations, predicting the dominant product to be vinylcyclopropane produced by a di-pi-methane rearrangement, and the favored [2 + 2] cycloaddition product to be bicyclo[2.1.0]pentane. Reaction pathways involving initial C-C or C-H bond cleavage were found to be too high in energy to be significant. Both the [2 + 2] cycloadditions and the di-pi-methane rearrangement proceed through cyclic biradical intermediates formed on the triplet surface. The relative rates of formation of these triplet biradicals are found to depend on three factors: biradical stability, the geometry of the transition structure, and orbital interactions through bonds.
利用密度泛函理论（UB3LYP）和从头算（CASSCF）方法，采用6-31G基组对1,4-戊二烯的三重态反应进行了研究。研究了分子内[2 + 2]光环加成反应以及导致乙烯基环丙烷的三种不同反应途径。计算结果与实验观测结果吻合良好，预测主要产物是通过双π-甲烷重排生成的乙烯基环丙烷，而最有利的[2 + 2]环加成产物是双环[2.1.0]戊烷。发现涉及初始C-C或C-H键断裂的反应途径能量过高，不太可能发生。[2 + 2]环加成反应和双π-甲烷重排均通过在三重态表面形成的环状双自由基中间体进行。发现这些三重态双自由基的相对形成速率取决于三个因素：双自由基稳定性、过渡结构的几何形状以及通过键的轨道相互作用。
