Department of Chemistry, School of Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan.
Chem Commun (Camb). 2012 Sep 28;48(75):9334-42. doi: 10.1039/c2cc34244h. Epub 2012 Jul 24.
This article provides an overview on the aromatic systems of four-membered rings. These aromatic four-membered ring systems are rather exotic because of a poor correspondence between the Hückel rule and the structure of four-membered rings. Consequently, such aromatics are generally dications or dianions, to form 2π or 6π electron systems respectively. Alternatively, the use of open-shell structures or empty d-orbitals of transition metal atoms could give neutral aromatic four-membered ring systems. This paper summarizes the four-membered aromatic compounds reported to date and describes the various methods for evaluating their aromaticity.
本文概述了四元环的芳香体系。由于休克尔规则与四元环结构之间的对应关系较差，这些芳香四元环体系相当奇特。因此，这些芳香体系通常为二阳离子或二阴离子，分别形成 2π 或 6π 电子体系。或者，使用开壳层结构或过渡金属原子的空 d 轨道可以得到中性芳香四元环体系。本文总结了迄今为止报道的四元芳香化合物，并描述了评估其芳香性的各种方法。
