Kwaśniewicz Michał, Czarnecki Mirosław A
49572 Faculty of Chemistry, University of Wrocław, Wrocław, Poland.
Appl Spectrosc. 2018 Feb;72(2):288-296. doi: 10.1177/0003702817732253. Epub 2017 Nov 14.
Effect of the chain length on mid-infrared (MIR) and near-infrared (NIR) spectra of aliphatic 1-alcohols from methanol to 1-decanol was examined in detail. Of particular interest were the spectra-structure correlations in the NIR region and the correlation between MIR and NIR spectra of 1-alcohols. An application of two-dimensional correlation analysis (2D-COS) and chemometric methods provided comprehensive information on spectral changes in the data set. Principal component analysis (PCA) and cluster analysis evidenced that the spectra of methanol, ethanol, and 1-propanol are noticeably different from the spectra of higher 1-alcohols. The similarity between the spectra increases with an increase in the chain length. Hence, the most similar are the spectra of 1-nonanol and 1-decanol. Two-dimensional hetero-correlation analysis is very helpful for identification of the origin of bands and may guide selection of the best spectral ranges for the chemometric analysis. As shown, normalization of the spectra pronounces the intensity changes in various spectral regions and provides information not accessible from the raw data. The spectra of alcohols cannot be represented as a sum of the CH, CH, and OH group spectra since the OH group is involved in the hydrogen bonding. As a result, the spectral changes of this group are nonlinear and its spectral profile cannot be properly resolved. Finally, this work provides a lot of evidence that the degree of self-association of 1-alcohols decreases with the increase in chain length because of the growing meaning of the hydrophobic interactions. For butyl alcohol and higher 1-alcohols the hydrophobic interactions are more important than the OH OH interactions. Therefore, methanol, ethanol, and 1-propanol have unlimited miscibility with water, whereas 1-butanol and higher 1-alcohols have limited miscibility with water.
详细研究了链长对从甲醇到1-癸醇的脂肪族一元醇的中红外（MIR）和近红外（NIR）光谱的影响。特别令人感兴趣的是近红外区域的光谱-结构相关性以及一元醇的中红外和近红外光谱之间的相关性。二维相关分析（2D-COS）和化学计量学方法的应用提供了关于数据集中光谱变化的全面信息。主成分分析（PCA）和聚类分析表明，甲醇、乙醇和1-丙醇的光谱与高级一元醇的光谱明显不同。光谱之间的相似性随着链长的增加而增加。因此，1-壬醇和1-癸醇的光谱最相似。二维异相关分析对于识别谱带的起源非常有帮助，并且可以指导化学计量分析的最佳光谱范围的选择。如图所示，光谱归一化突出了各个光谱区域的强度变化，并提供了原始数据无法获得的信息。醇的光谱不能表示为CH、CH和OH基团光谱的总和，因为OH基团参与了氢键作用。结果，该基团的光谱变化是非线性的，其光谱轮廓无法得到恰当解析。最后，这项工作提供了大量证据表明，由于疏水相互作用的重要性不断增加，一元醇的自缔合程度随着链长的增加而降低。对于丁醇和高级一元醇，疏水相互作用比OH-OH相互作用更重要。因此，甲醇、乙醇和1-丙醇与水无限混溶，而1-丁醇和高级一元醇与水有限混溶。
