Martin Ned H, Rowe Jimmy E, Pittman Eddie LaReece
Department of Chemistry and Biochemistry, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC 28403-5932, USA.
J Mol Graph Model. 2009 Jun-Jul;27(8):853-9. doi: 10.1016/j.jmgm.2009.01.002. Epub 2009 Jan 22.
The GIAO-HF method within Gaussian 03 was used to calculate the isotropic shielding value of the proximal hydrogen of a diatomic hydrogen probe at various distances (2.5 A, 3.0 A and 4.0 A) above the plane of 15 conjugated five-membered ring heterocyclic compounds: pyrrole, furan, thiophene, and phosphole and their 2- and 3-nitrogen analogs. Subtraction of the isotropic shielding value of diatomic hydrogen by itself from each of these isotropic shielding values gave the shielding increment (Deltasigma) for each probe position. Plotting Deltasigma against Cartesian coordinates of the probe position allowed determination of the computed through-space shielding increment surfaces for these compounds. Substantial shielding was observed above the center of each ring, as expected for aromatic compounds. The magnitude of the shielding increment at 2.5 A above the ring center (Deltasigma(2.5)) correlated reasonably well with other established methods of assessing aromaticity, including geometric (HOMA, harmonic oscillator model of aromaticity), energetic (ASE, aromatic stabilization energy), and magnetic (NICS, nucleus-independent chemical shift) criteria.
使用高斯03中的GIAO-HF方法计算双原子氢探针的近端氢在15种共轭五元环杂环化合物（吡咯、呋喃、噻吩、磷杂环戊二烯及其2-和3-氮类似物）平面上方不同距离（2.5埃、3.0埃和4.0埃）处的各向同性屏蔽值。从这些各向同性屏蔽值中分别减去双原子氢自身的各向同性屏蔽值，得到每个探针位置的屏蔽增量（Δσ）。将Δσ与探针位置的笛卡尔坐标作图，可以确定这些化合物的计算空间屏蔽增量表面。正如芳香族化合物所预期的那样，在每个环的中心上方观察到了显著的屏蔽。环中心上方2.5埃处的屏蔽增量大小（Δσ(2.5)）与其他已确立的评估芳香性的方法，包括几何方法（HOMA，芳香性的谐振子模型）、能量方法（ASE，芳香稳定能）和磁性方法（NICS，核独立化学位移）标准，有较好的相关性。
