S→N烷基重排反应的机理和溶剂化效应

Mechanism and solvent effect of S→N alkyl rearrangement

采用密度泛函理论的B3LYP方法、从头算的MP2方法和自洽反应场极化连续模型(PCM),在6-311++G(2d,2p)基组水平上研究了N,N’-二甲基-S-异苯并呋喃在气相和溶液中发生S→N烷基重排反应的机理、溶剂效应和取代基效应.结果表明:该反应通过四元环机理和双位迁移机理生成产物,在气相和溶剂水中,双位迁移途径的能垒均比四元环途径低,反应主要通过双位迁移途径生成产物.在气相,苯环上发生-Cl,-NO2和-OCH3取代时,双位迁移途径的能垒在MP2/6-311++G(2d,2p)水平上比没有取代时分别低4.18,7.61,4.96kJ/mol,反应的取代基效应不明显.而在溶剂水中,苯环上发生-Cl,-NO2和-OCH3取代时,双位迁移途径的能垒在PCM-MP2/6-311++G(2d,2p)水平上比气相时分别低37.73,39.96和37.17kJ/mol,反应的溶剂化效应非常明显.理论研究结果与实验观察结果一致.

The SS→N alkyl rearrangement mechanism and substituted effect and solvent effect of the N, N＇-dimethyl-S-isobenzofuranon are studied by B3LYP, MP2 methods and the polarizable continuum model（PCM） with 6-311＋＋G（2d,2p） basis set. The results show that the reaction occurs through the four-membered ring and the two consecutive back-side pathways to yield the products. The energy barrier of the two consecutive back-side pathway is lower than that of the four membered ring path- way. The reaction mainly occurs through the two consecutive back-side pathway both in gas phase and water. In gas phase, when -C1, -NO2 and -OCH3 substituents locate on the orthoposition of ben- zene, the energy barriers of the two consecutive back-side pathways are lower than these of the path- ways by 4.18,7.61,4.96 kJ/mol at the PCM-MP2/6-311＋＋G（2d,2p） level. The substituent effect is not obvious. In water, when -C1, -NO2 and -OCH3 substituents locate on the orthoposition of benzene, the energy barriers of the two consecutive back-side pathways are lower than these of the pathways in gas phase by 37.73, 39.96 and 37.17 kJ/mol at the PCM-MP2/6-311＋＋G（2d,2p） lev- el. The solvent effect is obvious. The theoretical results are consistent with the experimental observation.