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Temperature dependence of hydrogen bond structure by ^2D NMR.

通过^2D NMR 观察氢键结构的温度依赖性。

基本信息

批准号：
11640509
负责人：
KEISUKE Miyakubo
金额：
$ 2.11万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640509/
关键词：
hydrogen bond ^2D NMR nuclear quadrupole coupling constant hydrogen bond length hydrogen salt 水素結合長の温度変化重水素核共鳴低温プローブ

项目摘要

Many kinds of "hydrogen salt" make short hydrogen bonds with acidic hydrogen that is not substituted by metal ions. In such short hydrogen bonds, bond length and nuclear quadrupole coupling constant (QCC) have various values and their relation is not simple. This fact has been related to the change of potential energy surface that dominates the behavior of hydrogen bond. It becomes symmteric from asymetric, and its shape changes from double to single minimum shape with decreasing hydrogen bond length. However these distinctions is often difficult to account for both static and dynamic properties of hydrogen bond. In some very short hydrogen bond QCC increases with increasing temperature contrary to normal decreasing temperature dependence of QCC.Temperature dependence of QCC could be a good indicator of the nature of hydrogen bond because it varies not only its absolute value but also its sign. But a few observations was only exist. To proceed more detailed discussion, weUsing apparatus made in previous year, temperature dependences of 2D NMR spectra of acetylenedicarboxylic acid mono potassium salt (ADCAKH) with R_∞=2.445 Å and mono rubidium salt (ADCARbH) with R_∞=2.449 Å was observed. In both hydrogen salts, QCC increases linearly with increasing temperature. The temperature coefficients of both two salts are almost same, but the absolute value of QCC of ADCARbH is more than of ADCAKH in same order as their hydrogen bond length. If longer hydrogen bond length causes more QCC value, increase of QCC with increasing temperature would be explainable as an effect of thermal expansion of hydrogen bond.On the other hand, in potassium hydrogen carbonate with r_∞〜2.61 Å ^2D NMR spectra show slight decrease of QCC, and its temperature coefficient is very small. In KDCO_3, OH bond has a single bond character, therefore averaging effect due to anharmonic vibrational excitation of OH bond dominates the temperature dependence of QCC.

许多“氢盐”与未被金属离子取代的酸性氢形成短氢键。在如此短的氢键中，键长和核四极耦合常数(QCC)有不同的取值，它们之间的关系并不简单。这一事实与决定氢键行为的势能面的变化有关。随着氢键长度的减小，其形状从双最小形状变为单最小形状。然而，这些区别往往很难解释氢键的静态和动态性质。在一些很短的氢键中，QCC随温度的升高而增加，与QCC随温度的正常下降相反，QCC的温度依赖性不仅改变其绝对值，而且改变其符号，因此可以很好地指示氢键的性质。但当时只有几个观察结果。为了进行更详细的讨论，我们利用前年制造的装置，观察了R_∞=2.445Å的乙酰二元酸单钾盐(ADCAKH)和R_∞=2.449Å的RbH(ADCARbH)的2D核磁共振谱随温度的变化。在两种氢盐中，QCC均随温度的升高而线性增加。两种盐的温度系数基本相同，但ADCARbH的QCC绝对值大于ADCAKH的绝对值，与其氢键长度的大小顺序相同。如果氢键长度越长，Qcc值越大，则Qcc值随温度的升高可以解释为氢键的热膨胀效应。另一方面，在r_∞~2.61Å的碳酸氢钾中，二维核磁共振谱显示Qcc值略有下降，其温度系数很小。在KDCO_3中，OH键具有单键性质，因此OH键的非简谐振动激发的平均效应主导了QCC的温度依赖性。