Abstract：
Acetonitrile, a polar molecule that cannot form hydrogen bonds on its own, interacts with solvent molecules mainly through the lone pair of its nitrogen atom and the π electrons of its CN triple bond [Correction added on 17 July 2024, after first online publication: Acetole has been changed to Acetonitrile in the preceeding sentence.]. Interestingly, acetonitrile exhibits an unexpected strengthening of the triple bond\'s force constant in an aqueous environment, leading to an upshift (blueshift) in the corresponding stretching vibration: this effect contrasts with the usual consequence of hydrogen bonding on the vibrational frequencies of the acceptor groups, that is, frequency redshift. This investigation elucidates this phenomenon using Raman spectroscopy to examine the behavior of acetonitrile in organic solvent, water, and silver ion aqueous solutions, where an even more pronounced upshift is observed. Raman spectroscopy is particularly well suited for analyzing aqueous solutions due to the minimal scattering effect of water molecules across most of the vibrational spectrum. Computational approaches, both static and dynamical, based on Density Functional Theory and hybrid functionals, are employed here to interpret these findings, and accurately reproduce the vibrational frequencies of acetonitrile in different environments. Our calculations also allow an explanation for this unique behavior in terms of electric charge displacements. On the other hand, the study of the interaction of acetonitrile with water molecules and metal ions is relevant for the use of this molecule as a solvent in both chemical and pharmaceutical applications.
摘要：
乙腈,一个不能自己形成氢键的极性分子，主要通过其氮原子的孤对子和其CN三键的π电子与溶剂分子相互作用[在首次在线出版后，于2024年7月17日添加了更正：丙酮在前句中已更改为乙腈。].有趣的是,乙腈在水性环境中表现出三键力常数的意外增强，在相应的拉伸振动中导致升档（blueshift）：这种效果与氢键对受体组振动频率的通常结果形成对比，也就是说,频率红移。这项研究使用拉曼光谱来研究乙腈在有机溶剂中的行为，阐明了这种现象。水,和银离子水溶液，观察到更明显的升档。由于水分子在大部分振动光谱上的散射效应最小,拉曼光谱特别适用于分析水溶液。计算方法，静态和动态，基于密度泛函理论和混合泛函，被用来解释这些发现，准确再现不同环境下乙腈的振动频率。我们的计算也可以根据电荷位移来解释这种独特的行为。另一方面,乙腈与水分子和金属离子相互作用的研究与该分子在化学和制药应用中用作溶剂有关。
