Glycerol Esters

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H-NMR Spectroscopy of Fatty Acids and Their Derivatives – Esters other than methyl
1
H-NMR Spectroscopy of Fatty Acids and Their Derivatives
Glycerol Esters
Triacylglycerol esters are the most common esters in which fatty acids occur naturally. In nature,
triacylglycerols rarely exist in the form of a glycerol triester of only one fatty acid, but rather they
are mixed species, i.e. glycerol esterified with more than one fatty acid. Figures 1 to 3 (see
Appendix) depict 1H-NMR spectra of various glycerol esters of stearic acid.
Besides the tripling of the integration values of the protons in the fatty acid chain, the NMR
spectrum of tristearin, the triacylglycerol ester of stearic acid, shows the peaks for the sn-2 proton
at about 5.3 ppm (triplet of triplets) and two distinct absorptions (4.17 and 4.33 ppm; both are
doublets of doublets) of the sn-1 and sn-3 protons (HA1 and HA2; see structure inscribed in part a of
Figure 1 (Appendix)). These assignments have been described in the literature (Lie Ken Jie and
Lam, 1995), where also the dependence of these signals on the fatty acid chain attached to the
glycerol moiety are discussed. The sn-2 (HB) protons for the triacylglycerols of saturated fatty acids
were reported at 5.241-5.283 ppm in CDCl3, with values around 5.27 ppm common for mid-to longchain fatty acid moieties the sn-1 and sn-3 protons were reported at 4.142 to 4.161 ppm and 4.298
to4.326 ppm. The chemical shift ranges were similar for triacylglycerols of ABA and AAB type with
saturated fatty acid chains.
For triacylglycerols with acetylenic bonds with the
O CO (CH2)n C C (CH2)7CH3
structure illustrated (and with n = 0-10) the shifts were
observed at 4.299 - 4.338 ppm (HA2), 4.123-4.302 (HA1; with the extreme value of 4.302 ppm for n
= 0; n = 1 gave 4.231 ppm with increasing upfield shift with increasing n) and 5.260-5.331 ppm (HB;
again the extreme of 5.331 ppm for n = 0; n = 1 gave 5.305 ppm). The situation was more complex
for mixed triacylglycerols of AAB and ABA types with acetylenic fatty acids. For n ≥ 6, the positions
of the fatty acid chains could not be unambiguously determined.
For triacylglycerols of type AAA with fatty acid chains
O CO (CH2)n CH CH (CH2)7CH3
containing Z (cis) double bonds (fatty acid as illustrated
with n = 0-10), HA = 4.299 - 4.350 ppm (4.350 ppm for n
= 0; n = 1 gave 4.315 ppm), HA’ = 4.140 - 4.268 ppm (4.268 ppm for n = 0; n = 1 gave 4.180 ppm),
HB = 5.266 - 5.358 ppm (5.358 ppm for n = 0; n = 1 gave 5.284 ppm). For triacylglycerols of type
AAA with similar fatty acid chains but containing E (trans) double bonds, HA = 4.296 - 4.363 ppm
(4.363 ppm for n = 0; n = 1 gave 4.301 ppm), HA’ = 4.138 - 4.291 ppm (4.291 ppm for n = 0; n = 1
gave 4.165 ppm), HB = 5.263 - 5.384 ppm (5.384 ppm for n = 0; n = 1 gave 5.268 ppm).
G. Knothe
lipidlibrary.aocs.org
1
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H-NMR Spectroscopy of Fatty Acids and Their Derivatives – Esters other than methyl
Table 1. Chemical shift of protons in the fatty acid chains of AAA-type triacylglycerols. (Source: Lie
Ken Jie and Lam 1995). (a) Glyc = glycerol moiety.).
R (in Glyc-O-CO-R)
a)
Chemical shifts
C2
C3
CH2 C
CH2 C
C CH2
or
C CH2
CH CH
Saturated
CH3
2.073 (α), 2.087
(β)
2.353, 2.356
(CH2)2CH3
-
-
1.138, 1.144
-
-
2.307, 2.312
1.651, 1.659
-
-
(CH2)3CH3
2.324, 2.331
1.632
-
-
(CH2)4CH3
2.316, 2.321
1.623
-
-
(CH2)16CH3
2.307
1.609
-
-
-
-
2.334 (H-4)
-
3.269
-
2.181 (H-5)
-
2.111 (H-6)
-
2.217 (4-H); 2.127
(7-H)
2.146 (5-H and 8-H)
-
CH2CH3
Acetylenic
C
C (CH2)7CH3
CH2 C
C (CH2)7CH3
(CH2)2 C
C (CH2)7CH3
2.499 (m)
(CH2)3 C
C (CH2)7CH3
2.452
1.788
(CH2)4 C
C (CH2)7CH3
2.343
1.723
(CH2)7 C
C (CH2)7CH3
2.310
1.616
2.129 (8-H and
11-H)
-
5.762, 5.770
6.264, 6.278
2.635
3.101
see -CH=CH-
2.015 (5-H)
see H at C2 and
C3
5.325
-
Z-Ethylenic
CH CH (CH2)7CH3
CH2 CH CH (CH2)7CH3
(CH2)2 CH CH (CH2)7CH3
2.035 (6-H)
2.363
5.325; 5.403,
5.443
5.323; 5.391,
5.431
5.369
(CH2)3 CH CH (CH2)7CH3
2.322
1.675
(CH2)4 CH CH (CH2)7CH3
2.322
1.635
(CH2)7 CH CH (CH2)7CH3
2.309
1.610
1.999 (8-H and
11-H)
5.338
5.816, 5.829
6.986, 7.012
2.197
see 2-H and 3-H
CH2 CH CH (CH2)7CH3
3.031
see -CH=CH-
2.022 (5-H)
5.524
(CH2)2 CH CH (CH2)7CH3
2.358
2.308
1.951 (6-H)
5.420
(CH2)3 CH CH (CH2)7CH3
2.308
1.675
1.980 (4-H and 7-H)
5.381
(CH2)4 CH CH (CH2)7CH3
2.311
1.618
1.974 (5-H and 8-H)
5.380
(CH2)7 CH CH (CH2)7CH3
2.308
1.606
1.971 (8-H and
11-H)
5.379
2.056 (4-H), 1.991
(7-H)
2.036 (5-H and 8-H)
E-Ethylenic
CH CH (CH2)7CH3
G. Knothe
lipidlibrary.aocs.org
2
1
H-NMR Spectroscopy of Fatty Acids and Their Derivatives – Esters other than methyl
In 1,3-distearin (Figure 2 (Appendix)), the signals of the sn-1 and sn-3 protons overlap (4.20 ppm
integration value 4). The two remaining signals of integration value 1 are assigned to the protons at
sn-2, namely 4.13 ppm, (overlapping the signals of the sn-1 and sn-3 protons, proton attached to
the sn-2 carbon) and 2.48 ppm (doublet, OH proton at sn-2).
The 1H-spectrum of 1-monostearin (Figure 8 (Appendix)) is more complex. Each of the seven
protons on the glycerol moiety gives a distinct signal. The two slightly overlapping downfield
doublets of doublets at 4.18 and 4.25 ppm are again assigned to the carbon carrying the fatty acid
chain (sn-1), similar to the assignments in di- and tristearin. The multiplet signals of the two protons
directly attached to the sn-3 carbon are also split and observed at 3.64 and 3.73 ppm. The signal
of the proton attached to the sn-2 carbon is observed at 3.97 ppm. The signals of the hydroxy
protons overlap the triplet of the C2 protons in the fatty acid chain, giving this signal a theoretical
integration value of 4. These assignments are verified by 2D heteronuclear correlation.
Literature
1
Lie Ken Jie, M.S.F. and Lam, C.C. H-Nuclear magnetic resonance spectroscopic studies of saturated,
acetylenic and ethylene triacylglycerols. Chem. Phys. Lipids, 77, 155-171 (1995).
Gerhard Knothe
National Center for Agricultural Utilization Research, Agricultural Research Service,
U.S. Department of Agriculture, Peoria, IL, USA
th
Last updated: June 27 , 2014
G. Knothe
lipidlibrary.aocs.org
3
1
H-NMR Spectroscopy of Fatty Acids and Their Derivatives – Esters other than methyl
Appendix
Figure 1a. 1H-NMR spectrum of tristearin.
1.00
2.00
2.05
5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0
Chemical Shift (ppm)
Figure 1b. 1H-NMR spectrum of tristearin expanded in the region of 4-6 ppm.
G. Knothe
lipidlibrary.aocs.org
4
1
H-NMR Spectroscopy of Fatty Acids and Their Derivatives – Esters other than methyl
f
a HA
HB C O CO R
b H C OH c
HB
C O CO R
a HA
R = CH2 – CH2 – (CH2)14 – CH3
f
d
e
g
g
d
e
a
c
b
4.04 0.99
5.5
5.0
4.5
4.0
0.96 4.00
3.5
3.0
2.5
2.0
Chemical Shift (ppm)
4.09 56.08 6.00
1.5
1.0
0.5
0
Figure 2. 1H-NMR spectrum of 1,3-distearin.
G. Knothe
lipidlibrary.aocs.org
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1
H-NMR Spectroscopy of Fatty Acids and Their Derivatives – Esters other than methyl
h
a H
H C O CO R
b H C OH d
H C OH e
c H
R = CH 2 – CH 2 – (CH 2)14 – CH 3
f
i
h
g
i
d, e, f
a
b
g
c
0.96 0.99
1.93
0.98
5.5
5.0
4.5
4.0
3.5
2.00 28.03 3.00
3.93
3.0
2.5
2.0
1.5
1.0
0.5
0
Chemical Shift (ppm)
Figure 3. 1H-NMR spectrum of 1-monostearin.
G. Knothe
lipidlibrary.aocs.org
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