Epoxy Fatty Acids
1H-NMR Spectroscopy of Fatty Acids and Their Derivatives
Most epoxy compounds have signals for the protons attached to the epoxidized carbons at 2.7 ppm for cis and 2.45 ppm for trans (Gunstone and Jacobsberg, 1972). More details are given in Table 1.
|Table 1. Chemical shifts in methyl epoxyoctadecanoates (Gunstone and Jacobsberg, 1972). Solvent, carbon tetrachloride (CCl4). 220MHz. Recalculated from τ values given in the original literature.|
|Isomer (position of epoxy group)||CH3—||—CH2—COOMe|
|3,4||0.87||0.88||3.16, 2.85||2.56, 2.86||2.36, 2.60||2.30, 2.58|
|16,17||1.21||1.17||2.69, 2.83||2.52, 2.54||2.20||2.20|
|17,18||-||N/A||2.26, 2.53, 2.72||N/A||2.20||N/A|
In deuterobenzene (C6D6) (400 MHz), the shifts of the protons at C-9 and C-10 of methyl 9,10-epoxyoctadecanoate were reported at 2.97-3.02 as a broad singlet (Piazza et al., 2002).
Epoxyoctadecenoic, epoxyoctadecynoic and diepoxyoctadecanoic esters (220 MHz; CCl4) were also analysed (Gunstone and Schuler, 1975). In diepoxides, the signals of the protons on the epoxy carbons of diepoxystearates are found at about 2.70-2.95 ppm (cis epoxides) and 2.50-2.70 ppm (trans). Diepoxides separated by only one CH2 gave two signals caused by the inner and outer pairs of CH protons, cis,cis for example at 2.91 and 2.79 ppm (9, 12) or 2.93 and 2.81 (6, 9) as well as trans,trans (2.65 and 2.52). Similar results were obtained for methyl 9,10-12,13-diepoxy octadecanoate in C6D6, for which multiplets at 2.92-3.00 ppm (protons at C9 and C13) and 3.14-3.21 ppm (protons at C10 and C11) were reported besides a triplet at 1.82-1.87 ppm for the protons at C11 (Piazza et al., 2002). Four signals are observed for cis/trans epoxides (2.91, 2.78, 2.66, 2.55; 2.93, 2.78, 2.66, 2.55) (Gunstone and Schuler, 1975). This separation is not apparent when the epoxy groups are separated by more than one CH2 group but a slight downfield shift to 2.76 and 2.77 (two methylenes), 2.73 and 2.75 (three methylenes), 2.73 (four methylenes) and 2.72 (five methylenes). These shifts are less significant in unsaturated epoxides with the epoxy protons causing signals at 2.69-2.75 (cis) and 2.49-2.50 (trans; one methylene only); see below.
Unsaturated Epoxy Compounds
1H-NMR data have also been reported for some unsaturated epoxy compounds. Table 2 contains characteristic data for such fatty compounds.
|Table 2. Signals in the 1H-NMR of unsaturated methyl epoxyoctadecenoates|
|Double/ triple bond||Epoxy||—CH=CH—|
|9(Z)a||Z-12,13||5.33 (m, H-10); 5.43 (m, H-9)||2.82 (m, H-12 and H-13)||2.10, 2.27 (both m, each 1H of H-11)||1.44 (m, H-14)|
|9(Z)b||E-11,12||5.64-5.73 (m, H-9);
5.00-5.08 (m, H-10)
|3.31-3.35 (m, H-11);
2.79-2.83 (m, H-12)
|11(E)b||Z-9,10||5.92 (dt, H-12);
5.25-5.34 (m, H-11)
|3.36 (q, H-10); 3.01-3.09 (m, H-9)||2.01-2.12 (m, H-13),
1.46-1.52 (m, H-7 and H-8)
|9a,c||Z-11,12||-||2.95 (m, H-12); 3.41 (d, H-11)||2.21 (t<, H-8)|
|aMethyl ester of vernolic acid (methyl vernolate). Reference: Fürmeier and Metzger, 2003.
bReference: Lie Ken Jie et al., 2003.
cReference: Lie Ken Jie and Alam, 2001
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