Induced magnetic fields in aromatic [n]-annulenes—interpretation of NICS tensor components

The aromatic fluctuation index (FLU): A new aromaticity index based on electron delocalization

“…Following the plane's normal vector direction to a 1-Å distance from this site, we have reached the point to calculate the NICS͑1͒ for nonplanar species. The NICS outof-plane component corresponding to the principal axis perpendicular to the ring plane, NICS zz , which has been recently recommended as a more direct measure of induced ring current densities, 39 has been also calculated.…”

Efficient mapping of ring currents in fullerenes and other curved carbon networks

“…Such currents can be inferred indirectly from their effects on observable magnetic properties (exaltation of magnetisability [17][18][19], downfield chemical shifts of external hydrogen nuclei [20]) and properties that are sub-observables, in Hirschfelder's sense [21], such as the characteristically negative NICS value at the ring centre or some other chosen point [22]. Inferences of this type all have difficulties associated with masking of ring-current effects by other contributions to the property [23][24][25][26][27], but ring-current aromaticity can in fact be deduced directly from calculation of the induced current itself, by solution of the Schrödinger equation for the molecule immersed in the magnetic field, using an appropriate distributed-origin method [28][29][30][31]. The present paper is concerned with the application of this technique to fullerenes and similar curved-carbon molecules.…”

Study on the Aromaticity of Heterobenzenes C5H5X (X＝N, P, As, Sb, Bi) by Nucleus Independent Chemical Shifts (NICS) and Isomerization Stabilization Energies (ISE)

“…HF 方法相对合理还可以从另一个角度分析得到, 在标准条件下苯芳香性大于吡啶及其它杂苯分子 [17,43] , 当取 NICS(1)作为比较标准时, 从图 4 可以看出 MP2, X3LYP, B3LYP 计算结果并不满足上述条件, 它们的 NICS(1) zz 值将会产生比 NICS(max) zz 值大的计算误 差 [44] . 此外, 在不同的杂苯分子中, π轨道对其芳香性贡 献起主导作用, 其重叠程度会随原子类型的改变而变 化, 如果固定在某个点处的 NICS 值再用 zz 处的张量来 说明芳香性顺序势必不合理.…”

“…加之, 采用 zz 张量来表述 全局芳香性主要取决于 Pople 环电流模型在分子的 zz 张 量上有较大的诱导磁场, 其能代表分子产生的最大磁特 征. 可见在 HF 下取 NICS(max)处的 zz 处的张量能更好 的满足计算值与实验值的相关性 [25,41,44] .…”