Solid-state¹³C NMR Study on Order → Disorder Phase Transition in Oleic Acid

Abstract

The reversible solid-state phase transition between the γ and α phases of oleic acid was followed by 13C 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.

Structure and Segmental Motions in a Substituted Polythiophene: A Solid‐State NMR Study

“…However, we were unable to determine the precise motion experienced by the aromatic carbon atoms during the chromic transition. Usually, deshielding of carbon atoms in polymers containing double bonds is accompanied with changes in the FWHM30 and these two concomitant features are explained in terms of intermolecular deshielding effect of a carbon–carbon double bond. However, in the case of the PMBMT, there is no major change in FWHM upon heating.…”

‘Wax bloom’ on beeswax cultural heritage objects: Exploring the causes of the phenomenon

“…In the course of melting of the sample, a characteristic shift of 0.4–1.4 ppm to lower frequencies was observed with methyl, methylene and allylic peaks. These shifts were caused by an increase in the gauche conformation proportion at the proximity of the chain ends . Further, the intense peak at 32.4 ppm disappeared and instead, a group of peaks in the interval of 29.5–30.6 ppm was detected.…”

Constituents of Aquilaria sinensis Leaves Upregulate the Expression of Matrix Metalloproteases 2 and 9

“…Terpenoids: loliolide (AQ4) [ 17 ], phytol (AQ7) [ 18 ], squalene (AQ15) [ 19 ]; Ligand: syringaresinol (AQ12) [ 20 ]; Phenolics: p- hydroxybenzoic acid (AQ8) [ 18 ], β - truxinic acid (AQ10) [ 21 ], p- hydroxyphenethyl trans -ferulate (AQ13) [ 22 ]; Lipids: methyl (6 Z ,9 Z ,12 Z )-octadecatrienoate (AQ5) [ 23 ], palmitic acid and oleic acid (AQ6) [ 24 , 25 ], methyl-2-hydroxypentanedioate (AQ17) [ 26 ], glyceryl -9 Z -octadecenate (AQ21) [ 27 ], glyceryl 1-monononadecylate (AQ22) [ 28 ], 1-[nonadeca-(9Z,12Z)-dienoyl]-sn-glycerol (AQ23) [ 29 ]; Chromones: 7-hydroxy-6-methoxy-2-[2-(4′-methoxyphenyl)ethyl] chromone (AQ11) [ 30 ], 6-hydroxy-7-methoxy-2-[2-(3′-hydroxy-4′ -methoxyphenyl)ethyl] chromone (AQ16) [ 30 ]; Flavonoids: genkwanin (AQ1) [ 31 ], apigenin (AQ2) [ 32 ], velutin and pilloin (AQ3) [ 33 , 34 ];…”