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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Solid-state~(13)C NMR Study on Order → Disorder Phase Transition in Oleic Acid
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Solid-state~(13)C NMR Study on Order → Disorder Phase Transition in Oleic Acid

机译：固相〜（13）C NMR研究油酸中有序→无序相变

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摘要

The reversible solid-state phase transition between the γ and α phases of oleic acid was followed by ~(13)C solid-state NMR spectroscopy. All peaks in the γ and α phases were assigned based on the corresponding crystal structures determined by X-ray diffraction method (Abrahamsson and Ryderstedt-Nahringbauer, 1962, and Kaneko et al., 1996). As to the transition behavior, there was a significant difference between the two hydrocarbon chains straddling cis-olefin group. On the γ → α phase transition at 271 K, the methyl-sided methylene carbons exhibited upfield shifts due to the gauche effect. Characteristic peaks shifts due to the conformational change of the cis-olefin group were observed for cis-olefin carbons. On the other hand, the peaks due to carboxyl-sided chains showed no large shifts on this transition. Each oleic acid carbon atom showed a discontinuous decrease in T_1, except for the methyl carbon, which was in the extreme narrowing limit even in the γ phase. However, the T_1 values of the methyl-sided carbons were significantly smaller than those of the carboxyl-sided carbons in the α phase. The conformational disordering in the methyl-sided chains was accompanied by a remarkable increase of molecular motion in this moiety.
机译：油酸的γ相和α相之间可逆的固态相变之后是〜（13）C固态NMR光谱。 γ相和α相中的所有峰都是根据通过X射线衍射法确定的相应晶体结构分配的（Abrahamsson和Ryderstedt-Nahringbauer，1962; Kaneko等，1996）。关于过渡行为，跨越顺式-烯烃基团的两个烃链之间存在显着差异。在271 K时的γ→α相变上，由于丝网效应，甲基侧的亚甲基碳表现出高场位移。对于顺式烯烃碳，观察到由于顺式烯烃基的构象变化而引起的特征峰移动。另一方面，由于羧基侧链引起的峰在该跃迁上没有大的变化。除了甲基碳以外，每个油酸碳原子都显示出T_1的不连续降低，即使在γ相中，甲基碳也处于极窄的极限。然而，在α相中，甲基侧碳的T_1值显着小于羧基侧碳的T_1值。甲基侧链的构象紊乱伴随着该部分分子运动的显着增加。

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