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采用核磁共振氢谱(~1H NMR)和量子化学(QC)方法研究不同温度下乙醇水溶液和乙二醇水溶液中醇与水之间的相互作用。观察实验结果发现两种醇水溶液中水质子的化学位移呈现两种不同的变化趋势。随着含水量的增加,乙醇(ET)水溶液中水质子化学位移急剧降低,而乙二醇(EG)水溶液中水质子的化学位移缓慢增加。两种醇水溶液中的羟基质子随着浓度的增加,其共振峰移向低场。不同温度下随着浓度的增加两种醇水溶液的烷基质子共振峰单调的移向低场。几何结构优化结果表明醇羟基质子与水质子之间氢键的形成弱化了醇中O—H键,从而导致其键长增加。值得注意的是在相同的极化作用和扩散作用下采用密度泛函理论(DFT)(B3LYP)计算得到的ET和EG的C-H键,C-C键和O-H键的键长值大于采用HF理论计算得到的结果。与此相反的是采用HF理论得到的ET和EG的O-H…O键强度大于采用DFT(B3LYP)理论得到的结果。几何构型优化结果与实验结果相吻合。在NMR化学位移的计算中,就文中所提到的理论水平而言,DFT要优于HF。而对于同一理论,其基组越大,计算值越接近实验值。
The interaction between alcohol and water in ethanol aqueous solution and ethylene glycol aqueous solution at different temperatures was studied by 1H nuclear magnetic resonance (~ 1H NMR) and quantum chemical (QC) methods. The experimental results showed that the chemical shifts of water protons in two aqueous alcohol solutions showed two different trends. With the increase of water content, the proton chemical shift of aqueous solution in ethanol (ET) decreases sharply, while the chemical shift of proton in water of ethylene glycol (EG) increases slowly. The hydroxyl protons in the two alcoholic aqueous solutions shifted to the lower field with increasing concentration. At different temperatures, with the increase of concentration, the alkyl proton resonances of two kinds of alcohol aqueous solution monotonically shift to the low field. The geometric structure optimization results show that the formation of hydrogen bonds between the alcohol and hydroxyl protons weakens the O-H bond in the alcohol, resulting in an increase in the bond length. It is noteworthy that the bond length between the CH bond, the CC bond and the OH bond of ET and EG calculated by density functional theory (DFT) (B3LYP) under the same polarization and diffusion is larger than that calculated by HF theory the result of. In contrast, the O-H ... O bond strengths of ET and EG obtained using the HF theory are greater than those obtained using the DFT (B3LYP) theory. The geometric configuration optimization results are consistent with the experimental results. In the calculation of NMR chemical shifts, DFT is superior to HF in terms of the theoretical level mentioned in the text. For the same theory, the larger the basis set, the closer the calculated value is to the experimental value.