A3型Corrole中位取代基对其β位1H-NMR的影响

采用密度泛函(DFT)方法对八个中位有不同取代基的A3型corrole进行了几何结构优化和核磁共振(NMR)理论计算. 几何优化结果显示5,10,15-三苯基corrole的两个环内NH异构体的中位苯环空间排布方向不同. 此外, 虽然A3型corrole两个环内NH异构体A和B的能量相差不大, 但A和B分子的Boltzman分布概率却有较大的不同, 且受取代基影响很大. 因而在计算NMR时必须对A和B异构体的理论化学位移做Boltzman统计平均处理. NMR计算结果表明, 在B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d,p)水平下可以得到较为合理的corrole的1H-NMR化学位移结果. β-位氢的化学位移与取代基Hammett常数σ+P的大小成正比关系. 此外, 由于corrole大环的低对称性, 取代基对不同位置β-位氢的NMR影响程度不同, 其β-位氢化学位移的大小和顺序与中位取代基的电子效应和corrole的立体结构因素有关.

Effect of Meso-Substituents on β 1H-NMR of A3 Type Corrole

Geometries of eight A3-type corroles bearing different substituents were optimized and their nuclear magnetic resonance(NMR) propertieswere also calculated using density functional theory (DFT). Geometry optimization results showed that the NH tautomerization of 5,10,15-tris(phenyl)corrole is accompanied by the twisting of its phenyl groups. Although the total energies of both corrole NH tautomers are similar, the Boltzmann distribution probabilities of the A and B tautomers are significantly different. It is also dependent on the meso-substituents. Boltzman statistic averaging should thus be used to evaluate the 1H-NMR of corrole. NMR calculations performed at B3LYP/6-311+G (2d,p)//B3LYP/6-31G(d,p) level may give reasonable 1H-NMR chemical shifts for the corrole. β-H chemical shifts were proportional to the Hammett constants σ+P of the substituents. Furthermore, because of the low symmetry of corrole, the substituents exerted a different effect on the NMR of β-protons at different positions. The order of 1H-NMR chemical shifts for different β-H is quite sensitive to the nature of meso-substituents. β1H-NMR is determined by the electronic effect of substituents and the geometrical structure of the corrole.