Su Ming-Der
Department of Applied Chemistry, National Chiayi University, Chiayi 60004, Taiwan.
Chemistry. 2007;13(35):9957-72. doi: 10.1002/chem.200700646.
The ground-, (1)(pipi*)-, and (3)(pipi*)-state potential-energy surfaces of 1,2-cyclononadiene and isomeric C(9)H(14) species, as well as 1-methyl-1,2-cyclononadiene and isomeric C(10)H(16) species were all mapped using CASSCF and the 6-31G(d) basis set. Theoretical results were found to be in good agreement with the available experimental observations for both 1,2-cyclononadiene and 1-methyl-1,2-cyclononadiene isomerization reactions under singlet and triplet direct or sensitized irradiation. Extremely efficient decay occurs from the first singlet excited state to the ground state through at least three different conical intersections (surface crossings). The first of these crossing points is accessed by a one-bond ring closure. From this conical intersection point (CI-A or CI-C), some possible subsequent ground-state reaction paths have been identified: 1) intramolecular C--H bond insertion to form the bicyclic photoproduct and 2) intramolecular C--H bond insertion to form tricyclic photoproducts. An excited state [1,3]-sigmatropic shift leads to the second conical intersection (CI-B or CI-E), which can give a three-bond cyclononyne species. Besides these, in the singlet photochemical reactions of 1-methyl-1,2-cyclononadiene, excited-state, one allenic C--H bond insertion leads to a third conical intersection (CI-D). Possible ground-state reaction pathways from this structure lead to the formation of a diene photoproduct or to transannular insertion photoproducts. Moreover, in the case of triplet 1,2-cyclononadiene and 1-methyl-1,2-cyclononadiene photoisomerization reactions, both chemical reactions will adopt a 1,3-biradical (T(1)/S(0)-1, T(1)/S(0)-2, and T(1)/S(0)-3), which may undergo intersystem crossings leading to the formation of tricyclic or bicyclic photoproducts. The results obtained allow a number of predictions to be made.
使用CASSCF和6-31G(d)基组绘制了1,2-环壬二烯及异构C₉H₁₄物种、1-甲基-1,2-环壬二烯及异构C₁₀H₁₆物种的基态、(1)(ππ*)态和(3)(ππ*)态势能面。理论结果与1,2-环壬二烯和1-甲基-1,2-环壬二烯在单重态和三重态直接或敏化照射下异构化反应的现有实验观测结果高度吻合。从第一单重激发态到基态通过至少三个不同的锥形交叉点（表面交叉）发生极其有效的衰变。这些交叉点中的第一个可通过一键闭环进入。从这个锥形交叉点（CI-A或CI-C），已确定了一些可能的后续基态反应路径：1）分子内C-H键插入形成双环光产物；2）分子内C-H键插入形成三环光产物。一个激发态[1,3]-σ迁移导致第二个锥形交叉点（CI-B或CI-E），其可产生三键环壬炔物种。除此之外，在1-甲基-1,2-环壬二烯的单重态光化学反应中，激发态的一个丙二烯C-H键插入导致第三个锥形交叉点（CI-D）。从该结构出发的可能基态反应路径导致形成二烯光产物或跨环插入光产物。此外，在三重态1,2-环壬二烯和1-甲基-1,2-环壬二烯光异构化反应的情况下，两个化学反应都将采用1,3-双自由基（T(1)/S(0)-1、T(1)/S(0)-2和T(1)/S(0)-3），其可能经历系间窜越导致形成三环或双环光产物。所得结果使得能够做出一些预测。
