Origin of the attraction in aliphatic C-H/π interactions:: Infrared spectroscopic and theoretical characterization of gas-phase clusters of aromatics with methane
Origin of the attraction in aliphatic C-H/π interactions:: Infrared spectroscopic and theoretical characterization of gas-phase clusters of aromatics with methane
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DOI：
10.1021/jp064297k
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发表时间：
2006-09-14
影响因子：
2.9
通讯作者：
Tsuzuki, Seiji
中科院分区：
文献类型：
--
作者：
Morita, So-ichi;Fujii, Asuka;Tsuzuki, Seiji
用红外光谱和高水平从头算方法研究了脂肪族C-H键与π电子体系之间的相互作用（C-H/π相互作用）。用红外光谱法研究了气相中甲烷与苯、甲苯、对二甲苯、均三甲苯和萘形成的团簇，观察了团簇形成后甲烷部分C-H伸缩带的光谱变化。在理论方法中，团簇的相互作用能通过高级从头计算进行了评估。红外光谱中出现了微弱的C-H伸缩跃迁，证实了从头计算预测的甲烷分子在T-d对称性下发生了小的形变.另一方面，退化的非对称C-H伸缩带表现出复杂的分裂，这是定性的受阻转子模型解释。在对称C-H伸缩振动频率中发现了簇形成时的低频移动，但移动的幅度非常小，与相互作用能没有明显的相关性，而相互作用能的大小与芳烃的极化率有很好的相关性.同时还观察到了芳香基团的S-1-S-0电子跃迁，并在簇合物形成时出现低频位移。这些结果支持了在脂肪族C-H/π相互作用中分散相互作用超过静电和电荷转移项的优势。
An attractive intermolecular interaction between an aliphatic C-H bond and pi-electron system (C-H/pi interaction) was characterized on the basis of infrared spectroscopy and high level ab initio calculations. Infrared spectroscopy was applied to several isolated methane clusters with benzene, toluene, p-xylene, mesitylene, and naphthalene in the gas phase, and the spectral changes of the C-H stretch bands in the methane moiety upon the cluster formation were observed. In the theoretical approach, interaction energies of the clusters were evaluated by high-level ab initio calculations. The forbidden symmetric C-H stretch transition weakly appeared in the IR spectra of the clusters, and it confirmed the small deformation of the methane moiety from the T-d symmetry, which was predicted by the ab initio calculations. On the other hand, the degenerated asymmetric C-H stretch band showed complicated splitting, which is qualitatively interpreted by a hindered rotor model. Low-frequency shifts upon the cluster formation were seen in the symmetric C-H stretch frequency, though the magnitude of the shifts was extremely small and no clear correlation with the interaction energy was found. On the other hand, the size of the calculated interaction energy well correlates with the polarizability of aromatics. The S-1-S-0 electronic transition of the aromatic moiety was also observed, and it showed low-frequency shifts upon cluster formation. These results support the dominance of the dispersion interaction over the electrostatic and charge-transfer terms in the aliphatic C-H/pi interaction.