硫代樟脑光化学反应的理论研究  

Theoretical Study on Photochemical Reaction of Thiocamphor

作　　者：林玲[1] 丁万见[1] 方维海[1] 于建国[1] 刘若庄[1] 

机构地区：[1]北京师范大学化学学院,北京100875

出　　处：《化学学报》2007年第3期191-196,共6页Acta Chimica Sinica

基　　金：国家自然科学基金(Nos.20403003;20472011;20233020;20573011);国家重点基础研究发展计划(Nos.2004CB719903;2002CB613406)资助项目

摘　　要：运用量子化学方法优化了硫代樟脑的最低5个电子态(S0,T1,S1,T2和S2)的结构,并计算了它们的相对能量.计算结果表明:S1,T1和T2态的能量非常接近,而S2的能量远远高于T2态,这与之前对几种小的硫代羰基化合物的研究结论一致.确定了硫代樟脑分子在T1态发生β-插入反应和类Norrish II型反应的机理,计算的势垒相对于S0的振动零点分别为314.1和332.6kJ/mol.在400nm波长的光的照射下,分子被激发到S1态,此时分子没有足够的能量发生反应,只能通过内转换回到基态.当激发光波长在254nm时,硫代樟脑分子被激发到S2态,这时候体系有了足够的内部能量使反应发生.实验上已经观察到此激发光波长下,气态硫代樟脑可以发生β-插入反应和类Norrish II型反应.In the present work, the CASSCF method was employed to optimize structures of thiocamphor in the lowest five electronic states （S0, T1, S1, T2, and S2）, which was followed by single-point energy calculations at the MR-CI level. The energy gaps among the S1, T1 and T2 states are very small, but the S2 state is much higher than the T2 state in energy. Similar results were found for other thiocarbonyl compounds. The T1 potential energy profiles of the β-insertion and Norrish Ⅱ-like reactions were characterized by the B3LYP calculations and the barriers were predicted to be respectively 314.1 and 332.6 kJ/mol with respect to the So zero-level. Upon irradiation of thiocamphor at 400 nm, the molecules excited to S1 state do not have enough internal energy to overcome the barrier on the T1 surface. Thus, the internal conversion to the ground state could be the most probable pathway for the S1 deactivation. However, photoexcitation at 254 nm results in the molecules populated in the S2 state. In this case, the system has sufficient internal energy to undergo the β-insertion and Norrish Ⅱ-like reactions. Indeed, the two reactions have been observed experimentally.

关 键 词：硫代樟脑 光化学 从头算 

分 类 号：O644.1[理学—物理化学]