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The excited state antiaromatic benzene ring: a molecular Mr Hyde?
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
2015 (English)In: Chemical Society Reviews, ISSN 0306-0012, E-ISSN 1460-4744, Vol. 44, no 18, 6472-6493 p.Article, review/survey (Refereed) Published
Abstract [en]

The antiaromatic character of benzene in its first pi pi(star) excited triplet state (T-1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Huckel's rule for the ground state (S-0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S-1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

Place, publisher, year, edition, pages
2015. Vol. 44, no 18, 6472-6493 p.
National Category
Chemical Sciences
URN: urn:nbn:se:uu:diva-264929DOI: 10.1039/c5cs00057bISI: 000360654900008PubMedID: 25960203OAI: oai:DiVA.org:uu-264929DiVA: diva2:862182
Swedish Research CouncilWenner-Gren Foundations
Available from: 2015-10-20 Created: 2015-10-19 Last updated: 2015-10-20Bibliographically approved

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