Dissociation of dimeric cis-9-octadecenoic acid in its pure liquid state as observed by near-infrared spectroscopic measurement
Dissociation of dimeric cis-9-octadecenoic acid in its pure liquid state as observed by near-infrared spectroscopic measurement
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通过近红外光谱测量观察纯液态二聚顺-9-十八碳烯酸的解离
DOI：
10.1021/j100115a011
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Y. Ozaki
中科院分区：
文献类型：
--
作者：
M. Iwahashi;Norihisa Hachiya;Y. Hayashi;H. Matsuzawa;Masao Suzuki;Y. Fujimoto;Y. Ozaki
在8.6-84.4℃的温度范围内，用近红外光谱研究了C/í-9-十八烯酸二聚体在纯液体中解离成单体物种的过程，在1445 nm处出现了吸收峰，这是由于脂肪酸分子中的游离羟基在相对较低的温度下出现的，峰高随温度升高而增加。这表明酸性二聚体即使在较低温度下也会发生解离，并随温度的升高而增加。通过在很低浓度的四氯化碳溶液中的吸光度测量，得到了羧基上单体羟基伸缩模式在1445 nm处的摩尔吸收系数。纯样品在不同温度下的摩尔吸收系数和吸光度T，给出了二聚体c/j-9-十八碳烯酸在液体状态下分解成单体的离解程度a与温度的关系。At曲线在30℃和55℃有两个转折点，这两个转折点温度对应于Cir-9-十八烯酸液晶结构的转变温度：30℃对应准近晶液晶到更无序的液晶，55℃对应无序液晶和各向同性液体。1也就是说，c/S-9-十八烯酸的液态转变归因于二聚酸解离产生的单体分子的存在：以杂质形式存在的单体分子将在以CIí-9-十八烯酸二聚体为主的纯液体状态下引发转变。
The dissociation of dimers of c/í-9-octadecenoic acid into its monomeric species in its pure liquid was studied by near-infrared spectroscopic measurements over a temperature range of 8.6-84.4 C. An absorption band at 1445 nm, which is attributed to the free OH of the fatty acid molecules, appeared even at relatively low temperatures; its peak height increased with increasing temperature. This shows that the dissociation of the acid dimers occurs even at low temperatures andincreases with increasing temperature. The molar absorption coefficient at 1445 nm for the monomeric OH stretch mode in the carboxyl group was obtained through the absorbance measurements in carbon tetrachloride solution at very low concentrations. The molar absorption coefficient and the absorbance for the neat sample at various temperatures, T, give the temperature dependence of the degree of dissociation, a, for dimeric c/j-9-octadecenoicacid into monomers in the liquid state. The aT curve has two break points at 30 and 55 C. The break-point temperatures correspond to the transition temperatures in the liquid structures of cir-9-octadecenoic acid: 30 C corresponds to a quasi-smectic liquid crystal to a more disordered liquid crystal, and 55 C corresponds the disordered liquid crystal to isotropic liquid. 1 Namely, the transitions in the liquid state of c/s-9-octadecenoic acid are attributable to the presence of the monomeric molecules produced by the dissociation of the dimeric acid: The monomeric molecules existing as an impurity would initiate the transition in the pure liquid state consisting mainly of cií-9-octadecenoic acid dimers.