Toyama Yuta, Murakami Kohei, Yoshimura Norio, Takayanagi Masao
Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8, Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8, Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
Spectrochim Acta A Mol Biomol Spectrosc. 2018 May 15;197:148-152. doi: 10.1016/j.saa.2018.01.013. Epub 2018 Jan 5.
Even-odd alternation of the melting points of α,ω-disubstituted linear alkanes such as alkane-α,ω-diols, alkane-α,ω-dinitriles and α,ω-diaminoalkanes is well known. Melting points for compounds with an even number of carbons in their alkyl chains are systematically higher than those for compounds with an odd number of carbons. In order to clarify the origin of this alternation, near-infrared absorption spectra of linear alkane-α,ω-diols with 3 to 9 carbon atoms in their alkyl chains were measured in the liquid and solid states. The band due to the first overtone of the OH stretching mode was investigated. The temperature-dependent spectra of all alkane-α,ω-diols in their liquid states were found to be similar; no even-odd alternation was observed. In the solid state, however, spectra of alkane-α,ω-diols with even and odd numbers of carbon atoms differed greatly. Spectra of alkane-α,ω-diols with an odd number of carbon atoms in their solid states were similar to those in the liquid states, although the variation of spectra observed upon lowering the temperature of liquid seemed to continue when the liquids were frozen. In contrast, spectra of alkane-α,ω-diols with an even number of carbon atoms in their liquid and solid states were found to be quite different. New bands appeared upon freezing. The observed even-odd alternation of the spectra observed for alkane-α,ω-diols in their solid states is presumably caused by their even-odd alternation of crystal structures.
诸如烷烃-α,ω-二醇、烷烃-α,ω-二腈和α,ω-二氨基烷烃等α,ω-二取代直链烷烃的熔点奇偶交替现象是众所周知的。烷基链中碳原子数为偶数的化合物的熔点系统地高于碳原子数为奇数的化合物。为了阐明这种交替现象的起源，测量了烷基链中含有3至9个碳原子的直链烷烃-α,ω-二醇在液态和固态下的近红外吸收光谱。研究了OH伸缩振动模式的一次泛频引起的谱带。发现所有烷烃-α,ω-二醇在液态下的温度依赖光谱相似；未观察到奇偶交替现象。然而，在固态下，碳原子数为偶数和奇数的烷烃-α,ω-二醇的光谱有很大差异。固态下碳原子数为奇数的烷烃-α,ω-二醇的光谱与液态下的光谱相似，尽管当液体冷冻时，随着液体温度降低所观察到的光谱变化似乎会继续。相比之下，发现碳原子数为偶数的烷烃-α,ω-二醇在液态和固态下的光谱有很大不同。冷冻时会出现新的谱带。在固态烷烃-α,ω-二醇中观察到的光谱奇偶交替现象可能是由其晶体结构的奇偶交替引起的。
