Adaptive σ-Aromaticity in an Unsaturated Three-Membered Ring.,Chemistry - An Asian Journal

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Adaptive σ-Aromaticity in an Unsaturated Three-Membered Ring.
Chemistry - An Asian Journal ( IF 3.5 ) Pub Date : 2020-08-28 , DOI: 10.1002/asia.202000900
Yuanyuan Huang ₁ , Chenshu Dai ₁ , Jun Zhu ₁

Affiliation

Based on Hückel's and Baird's rules, species are aromatic either in the lowest singlet state (S₀) or the lowest triplet state (T₁) only. Thus, species with adaptive aromaticity (with aromaticity in both the S₀ and T₁ states) is particularly rare. On the other hand, σ‐aromaticity in the T₁ state has been underdeveloped, let alone adaptive σ‐aromaticity. Herein, via various aromaticity indices including NICS, ACID and EDDB, we demonstrate adaptive σ‐aromaticity in an unsaturated three‐membered ring, which is a traditional area dominated by π‐aromaticity. The origin of adaptive σ‐aromaticity could be attributed to the excitation mode of the T₁ state formed from out‐of‐plane π molecular orbital to the π* orbitals. Thus the σ‐aromaticity of the three‐membered ring in the S₀ state could hold in the T₁ state. Our findings extend the concept of adaptive σ‐aromaticity into three‐membered rings and could be useful to further develop the concept of both σ‐aromaticity and adaptive aromaticity.

中文翻译：

不饱和三元环中的自适应σ芳香性。

根据Hückel和Baird规则，物种仅在最低的单重态（S ₀）或最低的三重态（T ₁）下都是芳香族。因此，具有适应性芳香性（在S ₀和T _1两种状态下都具有芳香性）的物种特别少见。另一方面，在T ₁状态下的σ-芳香性还不发达，更不用说自适应σ-芳香性了。在此，我们通过包括NICS，ACID和EDDB在内的各种芳香性指标，证明了在不饱和三元环中的自适应σ-芳香性，这是一个以π-芳香性为主的传统区域。自适应σ芳香性的起源可归因于T ₁的激发模式从平面外π分子轨道到π*轨道形成的状态。因此，三元环在S ₀状态下的σ芳香性可以保持在T ₁状态。我们的发现将自适应σ-芳香性的概念扩展到三元环中，对于进一步发展σ-芳香性和自适应芳香性的概念可能有用。

更新日期：2020-11-04

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