Effect of size, charge, and spin state on Hückel and Baird aromaticity in [N]annulenes
The Hückel and Baird rules provide a framework to understand the aromaticity of monocyclic π-conjugated molecules in their singlet ground state and lowest-lying triplet state, respectively, particularly in the context of [N]annulenes. According to Hückel's rule, a molecule in the ground state i...
| Authors: | , , |
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| Format: | article |
| Status: | Published version |
| Publication Date: | 2025 |
| Country: | España |
| Institution: | Varias* (Consorci de Biblioteques Universitáries de Catalunya, Centre de Serveis Científics i Acadèmics de Catalunya) |
| Repository: | Recercat. Dipósit de la Recerca de Catalunya |
| OAI Identifier: | oai:recercat.cat:10256/26898 |
| Online Access: | http://hdl.handle.net/10256/26898 |
| Access Level: | Open access |
| Keyword: | Aromaticitat (Química) Aromaticity (Chemistry) Hückel, Regla de Hückel's rule Baird, Regla de Baird's rule Química orgànica Chemistry, Organic |
| Summary: | The Hückel and Baird rules provide a framework to understand the aromaticity of monocyclic π-conjugated molecules in their singlet ground state and lowest-lying triplet state, respectively, particularly in the context of [N]annulenes. According to Hückel's rule, a molecule in the ground state is aromatic if it contains 4n+2 π-electrons, while Baird's rule states that a molecule in the lowest-lying triplet state is aromatic if it contains 4n π-electrons, where n = 0, 1, 2, and so on. A previous study (J. Am. Chem. Soc. 2021, 143, 2403) examined the changes in the aromaticity of singlet ground-state [N]annulenes as the ring size increased from N = 12 to 66. However, no systematic investigation has yet been conducted for the lowest-lying triplet state of [N]annulenes or charged [N]annulenes. In this work, we address this gap by performing DFT calculations across several aromaticity descriptors, including structural, electronic, magnetic, and energetic indicators of aromaticity, with a particular focus on aromatic stabilization energies (ASEs). Our findings reveal that both neutral and charged [N]annulenes adhere to the Hückel and Baird rules. Nevertheless, for larger ring sizes, these rules diminish in significance, and the distinction between ASEs (and other indices of aromaticity) of [N]annulenes with 4n and 4n+2 π-electrons becomes less and less pronounced |
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