Rodgers Jeffrey M, Abaskharon Rachel M, Ding Bei, Chen Jianxin, Zhang Wenkai, Gai Feng
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Phys Chem Chem Phys. 2017 Jun 21;19(24):16144-16150. doi: 10.1039/c7cp02442h.
The C[double bond, length as m-dash]O/C[triple bond, length as m-dash]N stretching vibration arising from a carbonyl/nitrile functional group in various molecular systems has been frequently used to assess, for example, local hydrogen-bonding interactions, among other applications. However, in practice it is not always easy to ascertain whether the carbonyl or nitrile group in question is engaged in such interactions. Herein, we use 4-cyanoindole and cyclopentanone as models to show that, when a fundamental C[double bond, length as m-dash]O or C[triple bond, length as m-dash]N stretching mode is involved in Fermi resonance, the underlying vibrational coupling constant (W) is a convenient reporter of the hydrogen-bonding status of the corresponding carbonyl or nitrile group. Specifically, we find that for both groups a W value of 7.7 cm or greater is indicative of their involvement in hydrogen-bonding interactions. Furthermore, we find that, as observed in similar studies, the Fermi resonance coupling leads to quantum beats in the two-dimensional infrared spectra of 4-cyanoindole in isopropanol, with a period of about 1.9 ps.
在各种分子体系中，由羰基/腈官能团产生的C=O/C≡N伸缩振动常被用于评估例如局部氢键相互作用等多种应用。然而，在实际中，要确定所讨论的羰基或腈基是否参与了此类相互作用并不总是容易的。在此，我们以4-氰基吲哚和环戊酮为模型表明，当一个基本的C=O或C≡N伸缩模式参与费米共振时，潜在的振动耦合常数（W）是相应羰基或腈基氢键状态的一个方便的报告指标。具体而言，我们发现对于这两个基团，W值为7.7 cm或更大表明它们参与了氢键相互作用。此外，我们发现，正如在类似研究中观察到的那样，费米共振耦合导致异丙醇中4-氰基吲哚的二维红外光谱出现量子拍，周期约为1.9 ps。
