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应用量子化学方法,通过核独立化学位移(NICS)和异构体稳定化能(ISE)的计算,研究了苯及第五主族元素取代杂苯分子C5H5X(X=N,P,As,Sb,Bi)的芳香性与稳定性.局域轨道定位函数局部最大值的计算结果表明,分子中C—X成键强度与实验稳定性顺序一致.从头算与密度泛函理论对分子的化学位移计算结果各异,计算值与实验值相关分析表明,Hartree-Fock方法对所研究体系的NICS比密度泛函理论具有更好的相关性.在分子环平面上方0.8～0.9处的NICS是芳香性判据的最佳选择,由自然定域分子轨道分解NICS最大处的zz张量值,结果显示π键对分子的芳香性起主要贡献.异构体稳定化能与NICS(max)的zz张量及π键(NICS(max)zzπ)均有很好的相关性,可以表征杂苯分子C5H5X全局芳香性,其顺序为:苯>吡啶>磷杂苯>砷杂苯>锑杂苯>铋杂苯.特别地,对这类分子π轨道的研究发现不包含X原子的π轨道将产生异常大的π键芳香性,这一现象可为分子磁性设计提供理论指导.
Quantum chemical methods were used to study the interactions between benzene and the fifth main group of substituted benzene molecules C5H5X (X = N, P, As and Sb) by using NICS and ISE calculations. , Bi) .The calculation results of the local maxima of local orbital locating function show that the bonding strength of C-X in the molecule is consistent with the order of experimental stability.Accumulation and density functional theory The calculated results are different, and the correlation between the calculated value and the experimental value shows that the Hartree-Fock method has a better correlation with the NICS than the density functional theory of the system under study. The NICS at 0.8 ~ 0.9 above the plane of the molecular ring is aromatic The best choice for the criterion is to decompose the zz tensor value of the maximum NICS from a naturally localized molecular orbital, and the results show that the π bond plays a major role in the aromaticity of the molecule. The isomerization stability can be related to the zz sheet of NICS (max) (NICS (max) zzπ), which can be used to characterize the global aromaticity of C5H5X. The order is: benzene> pyridine> phosphazene> arsenate> antimony benzene> bismuth In particular, the study of π orbitals of these molecules found that π orbitals that do not contain X atoms would produce abnormally large Π bond aromaticity, this phenomenon can provide theoretical guidance for molecular magnetic design.