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Applicability of Baird’s Rule for In-Plane Aromaticity

submitted on 01.06.2021, 06:34 and posted on 02.06.2021, 09:42 by Yui Masumoto, Naoyuki Toriumi, Taisei Osawa, Atsuya Muranaka, Eiichi Kayahara, Shigeru Yamago, Mamoru Fujitsuka, Tetsuro Majima, Masanobu Uchiyama
Abstract: The concept of aromaticity is essential for chemists to understand the nature of many chemical substances. “In-plane” aromaticity is a unique type of aromaticity found in some π-conjugated systems consisting of radially oriented p-orbitals. Although in-plane aromaticity has been theoretically predicted about 40 years ago, its intrinsic properties are much less well understood than those of conventional Hückel aromatic systems with perpendicularly oriented p-orbitals because of lack of available examples of in-plane aromatic molecules. Here we demonstrate, from both theoretical and experimental aspects, that in-plane aromaticity of cycloparaphenylenes is reversed upon excitation to the lowest triplet state. In-plane non-aromatic neutral forms with a 4N-electron system and in-plane aromatic dications with a 4N+2-electron system turn out to be aromatic and anti-aromatic, respectively, indicating that Baird’s rule holds for the in-plane aromatic system. Armchair carbon nanotube fragments based on the cycloparaphenylene were also found to follow Baird’s rule from a magnetic viewpoint.


Development of molecular technology for linking matter and life with light

Japan Society for the Promotion of Science

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New Organic Chemistry and Materials Science of Curved pi-Conjugated Molecules

Japan Society for the Promotion of Science

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Synthesis of highly strained cycloparaphenylenes and elucidation of their properties

Japan Society for the Promotion of Science

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The Asahi Glass Foundation

NAGASE Science Technology Development

Sumitomo Foundation

Collaborative Research Program of Institute for Chemical Research, Kyoto University


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no conflict of interest

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