Department of Chemistry, Faculty of Science, Shizuoka University, Oya, Shizuoka 422-8529, Japan.
J Phys Chem A. 2012 Nov 29;116(47):11718-30. doi: 10.1021/jp310480d. Epub 2012 Nov 14.
According to the bridged annulene model, macrocyclic aromaticity of a porphyrinoid species can be attributed to the annulene-like main macrocyclic conjugation pathway (MMCP). Macrocyclic aromaticity, however, is given theoretically as a sum of contributions from all macrocyclic circuits. We found that the aromaticity due to each macrocyclic circuit is determined formally but broadly by Hückel's [4n + 2] rule of aromaticity. Nitrogen atoms in the pyrrolic rings effectively suppress the variation in the number of π electrons staying along each macrocyclic circuit. As a result, all or most macrocyclic circuits in oligopyrrolic macrocycles are made aromatic (or antiaromaitc) in phase with the MMCP. Thus, the MMCP is not a determinant of macrocyclic aromaticity but can be regarded as a good indicator of this quantity. This is why the bridged annulene model appears to hold for many porphyrins.
根据桥环薁模型，卟啉类物质的大环芳香性可以归因于类似薁环的大环共轭途径（MMCP）。然而，大环芳香性在理论上被定义为所有大环电路贡献的总和。我们发现，每个大环电路的芳香性在形式上但广泛地由休克尔的 [4n+2] 芳香性规则决定。吡咯环中的氮原子有效地抑制了沿每个大环电路的π电子数的变化。结果，寡吡咯大环中的所有或大多数大环电路与 MMCP 一致，呈现出芳香性（或反芳香性）。因此，MMCP 不是大环芳香性的决定因素，但可以被视为该性质的良好指标。这就是为什么桥环薁模型似乎适用于许多卟啉的原因。
