1H-NMR SPECTROSCOPY OF FATTY ACIDS AND THEIR DERIVATIVES
Acetylenic Fatty Acids and Derivatives
Table 1 contains some information on the 1H-NMR characterization of octadecynoic acids. Protons propargylic to triple bonds resonate at 2.05 to 2.3 ppm. The signals are split depending on the proximity of one of the triple bonds to C1 or the proximity of the triple bonds to each other. Similar values were given by Kannan et al. (1974) for stearolic acids (octadecynoic acids). In 10-undecynoic acid, the C11 proton was observed at 2.3 ppm and the C9 protons at 1.9 ppm. See also Frost and Gunstone (1975).
Table 1. Chemical shifts of octadecynoic acids. |
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| Triple bond position |
 |
 |
Literature |
|---|---|---|---|
| 2 | 2.33 | Gunstone and Ismail | |
| 2.34 (C4), 1.605 (C2) | Frost and Gunstone | ||
| 3 | 2.09 3.205 (acid), 3.135 (ester) |
2.140 (C5; acid and ester); 1.80 (C6; acid and ester) | Gunstone and Ismail Frost and Gunstone |
| 4 | 2.53 2.445 (acid); 2.330 (ester) |
2.10 (C6); 2.53 (C3) | Gunstone and Ismail |
| 5 | 2.30 2.075 (acid); 2.080 (ester) | 2.30 (C7); 1.90 (C3)
2.075 (C7); 2.200 (C3) acid 2.080 (C7); 2.160 (C3) ester |
Gunstone and Ismail Frost and Gunstone |
| 6 | 3.75 (?) 2.335 |
2.3-2.4 2.070 (C8), 1.725 (C5) |
Kannan et al. Frost and Gunstone |
| 7 | 2.315 | 2.070 (C9), 1.650 (C6) | Frost and Gunstone |
| 8 | no data available | ||
| 9 | 2.25 | Kannan et al. | |
| 10 | 2.10 | Gunstone and Ismail | |
The 11a to 15a isomers are identifiable by the absorption of the terminal methyl group, which is for these isomers (Frost and Gunstone, 1975): 11a: 0.895, 12a: 0.905, 13a: 0.925, 14a: 0.950 15a: 1.095 (spectra in carbon tetrachloride (CCl4)). For the 16a isomer, the values for CH3 at 1.72; C15 at 2.04, C14 at 1.40 and for the 17a isomer the values for C18 at 1.765; C16 at 2.125, C15 at 1.505 were characteristic.
Some other values of structural moieties containing triple bonds are given in Table 2.
Table 2. Frost and Gunstone (CPL, 1975) (CCl4, 220 MHz). |
|
| Protons | Signals |
|---|---|
 |
3.055-3.070 |
 |
2.980-2.990 |
 |
3.035-3.050 |
 |
2.330 |
 |
|
 |
|
 |
|
Gunstone et al. (1969) presented data on octadecadiynoic acids using the τ scale (TMS = 10 ppm).
9,12-Diunsaturates with double and/or triple bonds were also analysed (Gunstone and Jacobsberg, 1972; Table 3). Values for bis-propargylic protons at C11 are at 2.98 ppm, otherwise C11 protons are found at 2.62-2.79 ppm.
Table 3. Chemical shifts in 9,12-diunsaturated C18 fatty acids containing at least one triple bond (from Gunstone and Jacobsberg, 1972; literature values converted to δ scale). Solvent probably CCl4. |
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| Isomer |  |
 |
 |
 |
|---|---|---|---|---|
| 9i,12a | - | 2.98 | 2.09 | - |
| 9c,12a | 5.33 | 2.69 | 2.03 | 2.03 |
| 9a,12c | 5.32 | 2.69 | 2.07 | 2.02 |
| 9t,12a | 5.56, 5.28 | 2.67 | 2.11 | 1.98 |
| 9a,12t | 5.55, 5.28 | 2.67 | 2.09 | - |
Literature:
- Frost, D.J. and Gunstone, F.D. The PMR analysis of non-conjugated alkenoic and alkynoic acids and esters. Chem. Phys. Lipids, 15, 53-85 (1975).
- Kannan, R., Subbaram, M.R. and Achaya, K.T. NMR studies of some oxygenated, halogenated, and sulphur-containing fatty acids and their derivatives. Fette, Seifen, Anstrichm., 76, 344-350 (1974).
- Gunstone, F.D. and Ismail, I.A. Fatty Acids, Part 15. Nuclear magnetic resonance spectra of the cis octadecenoic acids and of some acetylenic acids. Chem. Phys. Lipids, 1, 337-340 (1967).
- Gunstone, F.D., Lie Ken Jie, M. and Wall, R.T. Fatty Acids. 23. Nuclear magnetic resonance spectra of some octadecadiynoic acids and of some methyl cis,cis- and trans,trans-octadecadienoates. Chem. Phys. Lipids, 3, 297-303 (1969).
- Gunstone, F.D. and Jacobsberg, F.R. Fatty Acids, Part 36. The synthesis, silver ion chromatographic, and nmr spectroscopic properties of the nine 9,12-diunsaturated n-C18 acids. Chem. Phys. Lipids, 9, 112-122 (1972).
National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL, USA
Updated: 16/1/2006 |
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