Tuoheti Qimanguli, Kerim Ablikim
The College of Chemistry and Chemical Engineering, Xinjiang University Urumqi 830046 China
RSC Adv. 2019 Aug 14;9(44):25351-25357. doi: 10.1039/c9ra04193a. eCollection 2019 Aug 13.
In this article, the topological resonance energy (TRE) method was used to investigate the global aromaticity of a set of [18]annulene-derived compounds which were obtained by replacing either two, four, or all six of the inner hydrogen atoms of [18]annulene with bridges (oxygen, imino-, sulfur, or combinations of the three). Our TRE results show that all the mono-bridged, di-bridged, and tri-bridged [18]annulenes are globally aromatic systems with positive TREs and show relatively larger aromaticity in comparison with the [18]annulene. The aromaticity of each compound was explained using the topological charge stabilization (TCS) rule. The bond resonance energy (BRE) and circuit resonance energy (CRE) methods were used to evaluate local aromaticity. Our BRE and CRE results show that incorporation of five-membered heterocyclic rings changes the main conjugation pathway of the bridged [18]-annulenes. The local aromaticities arising from the five-membered heterocyclic rings (6π) contribute strongly to global aromaticity. However, the ring current (RC), which arises from the 18π annulene-like pathway structures, is the primary determinant of the magnetic properties of the molecule. Our RC results are in good agreement with available H-NMR chemical shift data.
在本文中，采用拓扑共振能（TRE）方法研究了一组[18]轮烯衍生化合物的全局芳香性，这些化合物是通过用桥基（氧、亚氨基、硫或三者的组合）取代[18]轮烯内部的两个、四个或全部六个氢原子而得到的。我们的TRE结果表明，所有单桥、双桥和三桥[18]轮烯都是具有正TRE的全局芳香体系，与[18]轮烯相比显示出相对较大的芳香性。使用拓扑电荷稳定（TCS）规则解释了每种化合物的芳香性。采用键共振能（BRE）和回路共振能（CRE）方法评估局部芳香性。我们的BRE和CRE结果表明，五元杂环的引入改变了桥连[18]轮烯的主要共轭途径。五元杂环（6π）产生的局部芳香性对全局芳香性有很大贡献。然而，由类似18π轮烯途径结构产生的环电流（RC）是分子磁性的主要决定因素。我们的RC结果与现有的H-NMR化学位移数据吻合良好。
