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Rupturing aromaticity by periphery overcrowding

Saha, Promeet K.; Mallick, Abhijit; Turley, Andrew T.; Bismillah, Aisha N.; Danos, Andrew; Monkman, Andrew P.; Avestro, Alyssa-Jennifer; Yufit, Dmitry S.; McGonigal, Paul R.

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Promeet Saha
PGR Student Doctor of Philosophy

Abhijit Mallick

Andrew T. Turley


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.


Saha, P. K., Mallick, A., Turley, A. T., Bismillah, A. N., Danos, A., Monkman, A. P., …McGonigal, P. R. (2023). Rupturing aromaticity by periphery overcrowding. Nature Chemistry, 15(4), 516-525.

Journal Article Type Article
Acceptance Date Jan 26, 2023
Online Publication Date Mar 6, 2023
Publication Date 2023
Deposit Date Apr 26, 2023
Publicly Available Date Apr 26, 2023
Journal Nature Chemistry
Print ISSN 1755-4330
Electronic ISSN 1755-4349
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 15
Issue 4
Pages 516-525


Published Journal Article (2.6 Mb)

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