2-Aryl substituted 3-oxophenalenoxyl radicals: π-Spin structures and properties evaluated by dimer structure |
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| Institution: | 1. Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1,Toyonaka, Osaka 560-0043, Japan;2. Departments of Structural Molecular Science, The Graduate University for Advanced Studies, Myodaiji, Okazaki 444-8585, Japan;3. Departments of Chemistry and Materials Science, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan;4. Department of Chemistry, School of Science, Kitasato University, Kitasato, Sagamihara, Kanagawa 228-8555, Japan;5. PRESTO, Japan Science and Technology Agency, Honcho, Kawaguchi, Saitama 332-0012, Japan;1. Institute of Organoelement Compounds of the Russian Academy of Sciences, Vavilova St., 28, 119991, Moscow, Russian Federation;2. Carl von Ossietzky University of Oldenburg, 26129, Oldenburg, Germany;3. Department of Physics, The LNM Institute for Information Technology, Jamdoli, Jaipur, India;1. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan;2. Laboratoire de Chimie Théorique, University of Namur, rue de Bruxelles, 61, B-5000 Namur, Belgium;1. Key Laboratory of Green Chemistry & Technology of Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, China;2. State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, China |
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| Abstract: | We recently demonstrated that 6- and 4-oxophenalenoxyl radicals possess high stability in air due to extensive π-spin delocalization and steric protection of active sites. In sharp contrast, 3-oxophenalenoxyl radicals were found to be not stable enough to be isolated as an open-shell species, and easily dimerized with each other at 2-positions. The radicals were generated by thermal bond cleavage of the dimers in a solution state and their electronic structures were probed by ESR techniques. In this study, we have revealed a sterically hindered structure of the dimer of 2-(p-methoxyphenyl)-3-oxophenalenoxyl in terms of both X-ray crystal structure analysis and variable temperature 1H NMR studies. DFT calculations of the radicals indicate that π-spin densities dominantly exist at the 2-position, giving a rationale for the dimerized position of the radicals. These studies demonstrate that the lower stability of 3-oxophenalenoxyl is due to smaller π-spin delocalization into the whole phenalenyl skeleton than 6- and 4-oxophenalenoxyl radicals. |
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