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Aromaticity on the Pancake-Bonded Dimer of Neutral Phenalenyl Radical as Studied by MS and NMR Spectroscopies and NICS Analysis

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Shuichi Suzuki,^† Yasushi Morita,*^†^§ Kozo Fukui,^§ Kazunobu Sato,^‡ Daisuke Shiomi,^‡ Takeji Takui,*^‡ and Kazuhiro Nakasuji*^†

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan, Departments of Chemistry and Materials Science, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan, and PRESTO, Japan Science and Technology Agency (JST), Saitama 332-0012, Japan

J. Am. Chem. Soc., 2006, 128 (8), pp 2530–2531

DOI: 10.1021/ja058387z

Publication Date (Web): February 3, 2006

†

Osaka University.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

PRESTO-JST.

‡

Osaka City University.

, morita@chem.sci.osaka-u.ac.jp

Abstract

We have demonstrated the first MS and NMR observation of a face-to-face π-bonded dimer of an organic radical (pancake-bonded dimer coined by R. S. Mulliken) in solution, using tri-tert-butylated phenalenyl radical 1, a 3-fold symmetric neutral hydrocarbon. In addition to the direct detection of the dimer signal by cold-spray ionization mass spectrometry (CSI-MS), ¹H and ¹³C NMR spectra in solution gave definitive evidence of a well-defined D₃_d dimer structure with a 12-center-2-electron-long C−C bond formation, which is the same symmetry as seen in the crystalline state. On the basis of the NMR peaks of the dimer in the aromatic region (6.47 ppm for ¹H NMR and 120−143 ppm for ¹³C NMR), we carried out nucleus-independent chemical shift (NICS) analysis, which showed that the ring center of the dimer became more aromatic (−7.1 ppm) than that of the monomer (−3.8 ppm). The trend of aromaticity generation was more pronounced in the interior of the dimer, which has been interpreted by the negative electron density induced in the bonding region as seen in the electrostatic potential surface.

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Published In Issue March 01, 2006
Received December 10, 2005

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Communication

Aromaticity on the Pancake-Bonded Dimer of Neutral Phenalenyl Radical as Studied by MS and NMR Spectroscopies and NICS Analysis

Abstract

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History

Recommend & Share

Related Content

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Intermolecular π-to-π Bonding between Stacked Aromatic Dyads. Experimental and Theoretical Binding Energies and Near-IR Optical Transitions for Phenalenyl Radical/Radical versus Radical/Cation Dimerizations

Hybrid Density Functional Theory Studies on the Magnetic Interactions and the Weak Covalent Bonding for the Phenalenyl Radical Dimeric Pair

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