Torii Hajime, Noge Saori
Department of Chemistry, Faculty of Education, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan.
Phys Chem Chem Phys. 2016 Apr 21;18(15):10081-96. doi: 10.1039/c5cp08008h. Epub 2016 Mar 24.
Solvation-induced vibrational frequency shifts and infrared (IR) intensity changes of the hydrogen- or halogen-bond accepting stretching modes, especially their dependence on the angular position of the hydrogen- or halogen-bond donating molecule, are examined theoretically. Calculations are carried out for some modes of hydrogen- or halogen-bonding molecular complexes, including the S[double bond, length as m-dash]O stretch of dimethyl sulfoxide-(13)C2H2O, the C[triple bond, length as m-dash]N stretch of acetonitrileH2O, and the amide I' mode of the N-methylacetamide-d1BrNC 1 : 1 complex. It is shown that, in all the example cases dealt with in this study, the frequency shift depends rather strongly on the hydrogen- or halogen-bond angle (e.g., S[double bond, length as m-dash]OH angle), with a larger low-frequency shift as the hydrogen or halogen bond becomes more bent, indicating the generality of the results obtained for the amide I' mode of the N-methylacetamide-d1(2)H2O 1 : 1 complex in a previous study. Contrary to our vague expectation, the frequency shift is not well correlated to the hydrogen- or halogen-bond distance or strength, but nevertheless, it is well reproduced by an electrostatic interaction model if it is carefully constructed by considering the scalar and vector components separately in a reasonable way. On the basis of this electrostatic interaction model, the reason why our vague expectation is not realized is clarified, and a unified understanding is achieved on the hydration-induced high-frequency shift of the C[triple bond, length as m-dash]N stretch and the low-frequency shifts of the S[double bond, length as m-dash]O stretch and amide I'. With regard to the IR intensity, it is shown that, in some of the example cases, it also has rather strong angular position dependence. The mechanism of the IR intensity changes is estimated by analyzing the dipole derivative vector, especially its angular relation with the hydrogen or halogen bond.
从理论上研究了溶剂化诱导的氢键或卤键接受伸缩振动模式的振动频率位移和红外（IR）强度变化，特别是它们对氢键或卤键供体分子角位置的依赖性。对一些氢键或卤键分子复合物的模式进行了计算，包括二甲基亚砜 - (13)C2H2O的S = O伸缩振动、乙腈 - H2O的C≡N伸缩振动以及N - 甲基乙酰胺 - d1BrNC 1:1复合物的酰胺I'模式。结果表明，在本研究涉及的所有示例情况中，频率位移相当强烈地依赖于氢键或卤键角（例如S = OH角），随着氢键或卤键变得更加弯曲，低频位移更大，这表明先前研究中关于N - 甲基乙酰胺 - d1(2)H2O 1:1复合物的酰胺I'模式所获得的结果具有普遍性。与我们模糊的预期相反，频率位移与氢键或卤键距离或强度没有很好的相关性，然而，如果以合理的方式分别考虑标量和矢量分量来仔细构建静电相互作用模型，它可以很好地再现频率位移。基于这个静电相互作用模型，阐明了我们模糊预期未实现的原因，并对C≡N伸缩振动的水合诱导高频位移以及S = O伸缩振动和酰胺I'的低频位移达成了统一理解。关于红外强度，结果表明，在一些示例情况中，它也具有相当强的角位置依赖性。通过分析偶极导数矢量，特别是其与氢键或卤键的角度关系，估计了红外强度变化的机制。
