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以苯、甲苯及甲苯氯化反应所形成的σ络合物(中间体)为研究对象,运用密度泛函理论的B3LYP法,在6-311G~(DK2|**)水平上优化计算,并寻找σ络合物相互转化的过渡态。算出苯和甲苯的电荷分布、σ络合物的能量与电荷分布,以及σ络合物之间相互转化的过渡态的结构参数和能量。从电荷密度、σ络合物的稳定性及其相互转化机理3个方面,解释甲基的邻、对位的定位效应。为进一步研究取代基的定位效应,提供一些理论依据。
The sigma complexes (intermediates) formed by the chlorination of benzene, toluene and toluene were studied. The density functional theory (B3LYP) method was used to optimize the calculation at 6-311G ~ (DK2 **) Look for transition states of σ complexes. The charge distributions of benzene and toluene, the energy and charge distributions of σ complexes, and the structural parameters and energies of transition states between σ complexes were calculated. From three aspects of charge density, the stability of σ complex and its interconversion mechanism, the positioning effect of ortho and para to methyl is explained. In order to further study the positioning effect of substituents, provide some theoretical basis.