Aromaticity on the pancake-bonded dimer of neutral phenalenyl radical as studied by MS and NMR spectroscopies and NICS analysis.
Aromaticity on the pancake-bonded dimer of neutral phenalenyl radical as studied by MS and NMR spectroscopies and NICS analysis.
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DOI：
10.1021/ja058387z
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发表时间：
2006-02
影响因子：
15
通讯作者：
Shuichi Suzuki;Y. Morita;K. Fukui;Kazunobu Sato;D. Shiomi;T. Takui;K. Nakasuji
中科院分区：
文献类型：
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作者：
Shuichi Suzuki;Y. Morita;K. Fukui;Kazunobu Sato;D. Shiomi;T. Takui;K. Nakasuji
我们已经证明了第一个MS和NMR观察到的面对面的π键合的二聚体的有机自由基（煎饼键合的二聚体由R。S. Mulliken）在溶液中，使用三叔丁基化的非那烯基自由基1，一种3重对称中性烃。除了通过冷喷雾电离质谱法（CSI-MS）直接检测二聚体信号之外，溶液中的1H和13 C NMR光谱给出了明确的证据，即具有12中心2电子长的C-C键形成的明确定义的D3 d二聚体结构，这与在结晶状态中看到的对称性相同。基于芳香族区域中的二聚体的NMR峰（1H NMR为6.47 ppm，13 C NMR为120-143 ppm），我们进行了非核依赖化学位移（NICS）分析，其显示二聚体的环中心变得比单体的环中心（-3.8 ppm）更芳香（-7.1 ppm）。芳香性生成的趋势是更明显的内部的二聚体，这已被解释的负电子密度诱导的结合区域中看到的静电势表面。
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.