五员杂环化合物的量子化学理论研究

Quantum chemistry study of five heterocyclic compounds

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 Heterocyclic Compounds are important industrial raw material and some have significant physiological function. In this paper, we have studied the relation of the structure, chemical shift and reaction activeness of these kinds of compounds. Density functional B3LYP and ab initio HF,MP2 methods have been used to calculate the geometry structure of furan,pyrrole and thiophene molecules. Their electronic spectra have been obtained by the TD-DFT method. And the GAIO-HF method has been used to calculate the molecular chemistry shift. The calculated results are compared with the experimental values. The results show that ： （ 1 ） the MP2 method is more suitable for calculating the bond length and bond angle of these compounds. （2） The calculated electronic spectra show that the three compounds have the similar biggest absorption wavelength and the calculated value in the condition of solution is better than that of gas. （3）The chemical shift has a close relation with the reaction activeness：the smaller the 8H value of the alpha position hydrogen in the compound,the higher the electricity substitution activeness. For a heterocyclic molecule,the smaller the 8n value of the hydrogen atom,the higher the electricity substitution activeness in that position.