Work

The (Anti)aromatic Properties of Cyclo[n]Carbons: Myth or Reality?

Year: 2025

Type: article

Abstract: ABSTRACT Recent advances in on‐surface chemistry have enabled the synthesis and structural characterization of even‐numbered cyclo[n]carbons, traditionally classified as either doubly aromatic ( n = 4k + 2) or doubly antiaromatic ( n = 4k) based on their in‐plane and out‐of‐plane π‐electron circuits. However, recent studies have increasingly questioned this classification, suggesting instead that these molecules are more accurately described as non‐aromatic. In this work, we computationally examine the electron affinities and (anti)aromatic character of cyclo[n]carbons with n = 16–30 using energetic, structural, and electronic aromaticity descriptors. Adiabatic electron affinity (AEA) analysis reveals a high degree of uniformity across the series of both nominally aromatic and antiaromatic members. Aromatic stabilization energy (ASE) values, derived from homodesmotic and disproportionation reactions, indicate slight destabilization only for C 16 and C 20 , and low stabilization for the remaining systems. In particular, ASE is less than 2 kcal/mol for cyclo[n]carbons with n ≥ 24. This suggests that neither aromatic nor antiaromatic character significantly contributes to the thermodynamic stability of larger cyclocarbons. EDDB analysis further supports this conclusion, with only about 22%–27% of π‐electrons participating in delocalization. While delocalization is slightly greater in cyclo[n]carbons with n = 4k + 2, the difference diminishes with increasing size. Upon two‐electron reduction to the dianionic state, all cyclo[n]carbons exhibit bond length equalization and increased delocalization. These results suggest that only small cyclo[n]carbons ( n < 24) can be classified as weakly (anti)aromatic, while larger cyclo[n]carbons ( n ≥ 24) are more appropriately classified as non‐aromatic systems. The aromaticity of all considered cyclocarbons becomes more pronounced in corresponding dianionic forms due to cooperative structural and electronic effects. Thus, this work provides a unified framework for interpreting and predicting the electronic behavior of cyclocarbons.

Source: Journal of Computational Chemistry

DOI: 10.1002/jcc.70283

Authors: O. A. Stasyuk, G. George, C. Curutchet, F. Plasser, A. J. Stasyuk

Institutions: Universitat de Girona, Universitat de Barcelona, Loughborough University, University of Warsaw

Language: English

Topic: Synthesis and Properties of Aromatic Compounds

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,520

Funders: Ministerio de Ciencia, Innovación y Universidades, Agència de Gestió d'Ajuts Universitaris i de Recerca