Aromaticity and Antiaromaticity in the Low-Lying Electronic States of Cyclooctatetraene
Abstract
The levels of aromaticity of the most important geometries on the ground-state (S(0)), lowest triplet-state (T(1)), and first singlet excited-state (S(1)) potential energy surfaces (PESs) for cycloocta-1,3,5,7-tetraene (COT) are assessed using a wide range of magnetic criteria including nucleus-independent chemical shifts (NICSs), proton shieldings, and magnetic susceptibilities calculated using complete-active-space self-consistent-field (CASSCF) wave functions constructed from gauge-including atomic orbitals (GIAOs). It is shown that the ground state of D(8h) COT (transition state for the pi-bond-shift process on the S(0) PES) is markedly antiaromatic, even more so than the classical example of an antiaromatic system, the ground state of square cyclobutadiene. The CASSCF-GIAO magnetic properties of the ground state of D(4h) COT (transition state for the ring-inversion process on the S(0) PES) strongly suggest that it is much less antiaromatic than the ground state of D(8h) COT, whereas those of the ground state of D(2d) COT (local minimum on the S(0) PES) indicate that it is decidedly nonaromatic. The lowest triplet state and the first singlet excited state of D(8h) COT (local minima on the T(1) PES and the S(1) PES, respectively) exhibit surprisingly similar magnetic properties. These, in turn, are very close to the magnetic properties of benzene, which is a strong indication of a high degree of aromaticity.
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Karadakov showed in 2008 that Baird's rule also applies to the first excited singlet state, studying magnetic shielding of S1 benzene, square cyclobutadiene, and D8h cyclooctatetraene.
“In 2008, Karadakov showed that the rule also applies to the first excited singlet state, studying the magnetic shielding of S 1 benzene [193], square cyclobutadiene [193], and D 8h cyclooctatetraene (COT) [194].”
From Aromaticity and Antiaromaticity: How to Define Them (2025) · cites this paper as [194]
Cites
Which NICS Aromaticity Index for Planar π Rings Is Best?
Fallah-Bagher-Shaidaei, H., Wannere, C. S., Corminboeuf, C., Puchta, R., & Schleyer, P. V. R. (2006) · Organic Letters · doi:10.1021/ol0529546 · Cited by 1,257 · see citing works
Baird, N. C. (1972) · Journal of the American Chemical Society · doi:10.1021/ja00769a025 · Cited by 680 · see citing works
Cernusak, I., Fowler, P. W., & Steiner, E. (2000) · Molecular Physics · doi:10.1080/00268970050032792 · Cited by 81 · see citing works
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Rosenberg, M., Dahlstrand, C., Kilså, K., & Ottosson, H. (2014) · Chemical Reviews · doi:10.1021/cr300471v · Cited by 505 · see citing works
Karadakov, P. B., Hearnshaw, P., & Horner, K. E. (2016) · The Journal of Organic Chemistry · doi:10.1021/acs.joc.6b02460 · Cited by 96 · see citing works
Self-citationHow do the Hückel and Baird Rules Fade away in Annulenes?
Casademont-Reig, I., Ramos-Cordoba, E., Torrent-Sucarrat, M., & Matito, E. (2020) · Molecules · doi:10.3390/molecules25030711 · Cited by 71 · see citing works
“COT shows a boat-like D2d geometry that, although presents bond-length and bond-order alternation, is not a very antiaromatic molecule [16,85].”
BackgroundAromaticity and Antiaromaticity: How to Define Them
Baranac-Stojanović, M. (2025) · Chemistry · doi:10.3390/chemistry7040127 · Cited by 14 · see citing works
- Authors
- Karadakov, P. B.
- Affiliations
- University of York (GB)
- Corresponding author
- Karadakov, Peter B.
- ORCID
- Karadakov, Peter B.
- Venue
- The Journal of Physical Chemistry A
- Publisher
- American Chemical Society (ACS)
- Published
- 2008-11-13
- Volume
- 112
- Issue
- 49
- Pages
- 12707-12713
- ISSN
- 1089-5639 (ISSN-L)
- 1520-5215
- OpenAlex
- W1998648411
- Cited by
- 170
- References
- 3
- Citations by year
- 2026: 10 · 2025: 8 · 2024: 10 · 2023: 12 · 2022: 8 · 2021: 21 · 2020: 16 · 2019: 10 · 2018: 4 · 2017: 10 · 2016: 12 · 2015: 11 · 2014: 14 · 2013: 8 · 2012: 6
- FWCI
- 1.66
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- The Journal of Physical Chemistry A (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Chemistry › Organic Chemistry › Synthesis and Properties of Aromatic Compounds
- Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Advanced Chemical Physics Studies
- Physical Sciences › Chemistry › Organic Chemistry › Organic Chemistry Cycloaddition Reactions
- Keywords
- cyclooctatetraene, aromaticity, antiaromaticity, low-lying electronic states, potential energy surface, nucleus-independent chemical shift, magnetic properties, CASSCF, gauge-including atomic orbitals, ring inversion, triplet state, singlet excited state, benzene comparison
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