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五员杂环及衍生物是重要的工业原料,有些具有重要的生理作用。为了探讨此类化合物结构特点、化学位移与活性之间的关系,本文采用密度泛函B3LYP和从头计算ab initio HF、MP2方法研究了呋喃、吡咯、噻吩的几何构型,用TD-DFT方法对分子的电子光谱进行了计算,运用GAIO-HF计算了分子的化学位移,并将计算数据与实验值进行比较。结果表明：(1)选用MP2对此类化合物键长键角更为适宜；(2)三种化合物电子光谱的最大吸收波长很接近,溶液的计算值优于气相的；(3)分子的化学位移与反应活性有密切联系：化合物α位氢原子的δ_H值愈小,该化合物亲电取代反应活性愈高；同一杂环分子,氢原子的δ_H值愈小,该位置的亲电取代反应活性愈高。
Five-member heterocycles and derivatives are important industrial raw materials, some of which have important physiological roles. In order to explore the relationship between chemical structure and chemical shift of these compounds, the geometries of furan, pyrrole and thiophene were studied by density functional B3LYP and ab initio HF, MP2 ab initio methods. The TD-DFT method The electronic spectra of the molecules were calculated. The chemical shifts of the molecules were calculated using GAIO-HF, and the calculated data were compared with the experimental values. The results show that: (1) MP2 is more suitable for the bond length of these compounds; (2) the maximum absorption wavelength of the electronic spectra of the three compounds is very close and the calculated value of the solution is better than that of the gas phase; (3) Displacement is closely related to reactivity: the smaller the δ_H value of the hydrogen atom at the α position of the compound, the higher the electrophilic substitution reaction activity of the compound; the smaller the δ_H value of the hydrogen atom in the same heterocyclic molecule, the electrophilic substitution reaction activity The higher.