Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281 (S3), B-9000 Ghent, Belgium.
J Comput Chem. 2010 Sep;31(12):2286-93. doi: 10.1002/jcc.21520.
In a recent contribution, we examined the effect of 10- and 14-center circuits on the nucleus-independent chemical shifts NICSs using multicenter bond indices (MCBIs) (Fias et al., J Comput Chem 2008, 29, 358). In this study, the nonlocal contributions to the NICS are further investigated for a larger set of polycyclic aromatic hydrocarbons (PAHs). To achieve this, the NICSs are predicted using the MCBI and compared with ab initio results. The NICSs of the central ring of perylene- and benzo-[ghi]perylene-like fragments and of coronene appear to have other nonlocal contributions than the ones previously studied. It is shown that a model based on the MCBI-ring current maps and the inclusion of new circuits proves the existence and shows the nature of these new nonlocal effects on the NICS. This new model leads to a better understanding of the differences between the NICSs and delocalization indices. The results show that the NICS value is not only significantly influenced by the higher order circuits encircling the ring at which it is evaluated but also by the local aromaticity of the surrounding rings, and occasionally, like in the case of coronene, the NICSs are even influenced by currents farther away in the molecule.
在最近的一项贡献中，我们使用多中心键指标（MCBI）（Fias 等人，J Comput Chem 2008，29，358）研究了 10 中心和 14 中心环对核独立化学位移 NICS 的影响。在这项研究中，进一步研究了更大的多环芳烃（PAHs）系列中非局域对 NICS 的贡献。为了实现这一目标，使用 MCBI 预测 NICS，并将其与从头算结果进行比较。苝和苯并[ghi]苝类似片段的中央环以及 coronene 的 NICS 似乎具有与以前研究的不同的非局域贡献。结果表明，基于 MCBI-环电流图的模型和新环的包含证明了这些新的非局域效应的存在并显示了它们对 NICS 的性质。该新模型有助于更好地理解 NICS 和离域指数之间的差异。结果表明，NICS 值不仅受评估环周围的高阶环的显著影响，而且受周围环的局部芳香性的影响，并且在某些情况下，如 coronene，NICS 甚至受分子中更远的电流的影响。
