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

Citations Over TimeTop 10% of 2006 papers

Abstract

We have demonstrated the first MS and NMR observation of a face-to-face pi-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 D3d 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.

Related Papers

• → Quantum-chemical calculations of NMR chemical shifts of organic molecules: XII. Calculation of the 13C NMR chemical shifts of fluoromethanes at the DFT level(2014)9 cited
• → Theoretical evidence for the major isomers of fullerene C84 based on 13C NMR chemical shifts(2000)17 cited
• → Theoretical 13C and 15N NMR spectra for the C48N12 azafullerene(2003)13 cited
• การศกษาทางเคมคำนวณของ 1H-NMR และ 13C-NMR สเปกโทรสโกป ของ alpha-mangostin, gamma-mangostin และ Garcinone D(2011)
• Calculation of ~(13)C NMR Chemical Shifts in Aliphatic Ether(2007)