Department of Chemistry, Durham University, Durham, UK.
Department of Physics, Durham University, Durham, UK.
Nat Chem. 2023 Apr;15(4):516-525. doi: 10.1038/s41557-023-01149-6. Epub 2023 Mar 6.
The balance between strain relief and aromatic stabilization dictates the form and function of non-planar π-aromatics. Overcrowded systems are known to undergo geometric deformations, but the energetically favourable π-electron delocalization of their aromatic ring(s) is typically preserved. In this study we incremented the strain energy of an aromatic system beyond its aromatic stabilization energy, causing it to rearrange and its aromaticity to be ruptured. We noted that increasing the steric bulk around the periphery of π-extended tropylium rings leads them to deviate from planarity to form contorted conformations in which aromatic stabilization and strain are close in energy. Under increasing strain, the aromatic π-electron delocalization of the system is broken, leading to the formation of a non-aromatic, bicyclic analogue referred to as 'Dewar tropylium'. The aromatic and non-aromatic isomers have been found to exist in rapid equilibrium with one another. This investigation demarcates the extent of steric deformation tolerated by an aromatic carbocycle and thus provides direct experimental insights into the fundamental nature of aromaticity.
应变释放和芳香稳定之间的平衡决定了非平面π-芳香族化合物的形式和功能。已知拥挤系统会经历几何变形，但它们芳香环的有利的π电子离域通常得以保留。在这项研究中，我们使芳香族体系的应变能超过其芳香稳定能，导致其重排并破坏其芳香性。我们注意到，增加π-扩展薁环外围的空间位阻会导致它们偏离平面，形成扭曲的构象，其中芳香稳定和应变的能量接近。随着应变的增加，体系的芳香π电子离域被打破，导致形成非芳香的双环类似物，称为“Dewar 薁”。已经发现芳香和非芳香异构体之间存在快速平衡。这项研究划定了芳香碳环所能容忍的空间变形程度，从而为芳香性的基本性质提供了直接的实验见解。
