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Adaptive σ‐Aromaticity in an Unsaturated Three‐Membered Ring
Author(s) -
Huang Yuanyuan,
Dai Chenshu,
Zhu Jun
Publication year - 2020
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.202000900
Subject(s) - aromaticity , ring (chemistry) , chemistry , computational chemistry , molecule , organic chemistry
Based on Hückel's and Baird's rules, species are aromatic either in the lowest singlet state (S 0 ) or the lowest triplet state (T 1 ) only. Thus, species with adaptive aromaticity (with aromaticity in both the S 0 and T 1 states) is particularly rare. On the other hand, σ‐aromaticity in the T 1 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 T 1 state formed from out‐of‐plane π molecular orbital to the π* orbitals. Thus the σ‐aromaticity of the three‐membered ring in the S 0 state could hold in the T 1 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.