Blueshift of the CN stretching vibration of acetonitrile in solution: computational and experimental study,Journal of Computational Chemistry

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Blueshift of the CN stretching vibration of acetonitrile in solution: computational and experimental study
Journal of Computational Chemistry ( IF 3.4 ) Pub Date : 2024-06-20 , DOI: 10.1002/jcc.27452
Francesco Muniz-Miranda ₁ , Alfonso Pedone ₁ , Maria Cristina Menziani ₁

Affiliation

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 CN 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.

中文翻译：

溶液中乙腈CN伸缩振动的蓝移：计算和实验研究

乙腈是一种极性分子，本身不能形成氢键，主要通过其氮原子的孤对电子和其CN三键的π电子与溶剂分子相互作用[首次在线发布后于2024年7月17日添加更正: 前一句中的乙酮已更改为乙腈。]。有趣的是，乙腈在水环境中表现出意想不到的三键力常数增强，导致相应的伸缩振动上移（蓝移）：这种效应与氢键对受体基团振动频率的通常结果形成对比，即频率红移。这项研究利用拉曼光谱检查乙腈在有机溶剂、水和银离子水溶液中的行为来阐明这一现象，其中观察到更明显的上升。由于水分子在大部分振动光谱中的散射效应最小，拉曼光谱特别适合分析水溶液。这里采用基于密度泛函理论和混合泛函的静态和动态计算方法来解释这些发现，并准确地再现乙腈在不同环境中的振动频率。我们的计算还可以用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将该分子用作化学和制药应用中的溶剂相关。

更新日期：2024-06-20

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