Elaidic acid (trans-9-octa­decenoic acid)

Low, J.N.; Scrimgeour, C.; Horton, P.

doi:10.1107/S1600536805033040

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 61| Part 11| November 2005| Pages o3730-o3732

https://doi.org/10.1107/S1600536805033040

Elaidic acid (trans-9-octadecenoic acid)

John Nicolson Low,^a ^* Charlie Scrimgeour ^b and Peter Horton ^c

^aDepartment of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland, ^bScottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, and ^cEPSRC National Crystallography Service, School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, England
^*Correspondence e-mail: che562@abdn.ac.uk

(Received 11 October 2005; accepted 14 October 2005; online 19 October 2005)

Elaidic acid, C₁₈H₃₄O₂, has an essentially linear alkyl chain. The double bond is twisted across the mean direction of the alkyl chain in a skew′, trans, skew conformation. In the crystal structure, the molecules form centrosymmetric O—H⋯O hydrogen-bonded dimers (O⋯O = 2.684 Å).

Comment

The physical, biological and nutritional properties of fatty acids are largely determined by the number, position and configuration of their double bonds. These determine the shape of the molecules, the way molecules can pack together in solid phases, monolayers, bilayers etc., and how individual molecules can interact with enzymes and receptors. Most natural unsaturated fatty acids have cis (Z) double bonds. Trans (E) fatty acids are present in dairy fats and are produced during the catalytic partial hydrogenation used in the production of hardened fats and during deodorization of commodity oils. The labelling of foods with trans content is increasingly required due to their undesirable nutritional properties. Alternative ways of producing hardened fats, such as interesterification or blending with fully saturated fats, and milder deodorization procedures, are being developed to reduce trans content. Trans fatty acids more closely resemble saturated acids in melting point and nutritional properties, sharing an essentially linear structure which allows closely aligned packing in condensed phases. In contrast, cis double bonds introduce a bend in the alkyl chain, making packing less stable and lowering the melting point. We have determined the structure of elaidic acid (trans-9-octadecenoic acid), (I), to enable a detailed comparison of a trans fatty acid with saturated and cis-unsaturated compounds.

Relatively few crystal structures of fatty acids are available, as good crystals are difficult to obtain, often being thin plates and often crystallizing in several polymorphs. Most monoenes have low melting points and polyenes are liquids at room temperature. The crystal structures of the following saturated and monoene C₁₈ fatty acids have been reported to date: stearic acid (octadecanoic acid) (Malta et al., 1971 ; Kaneko et al., 1990 , 1994a ,b ), oleic acid (cis-9-octadecenoic acid) (Abrahamsson & Ryderstedt-Nahringbauer, 1962 ; Kaneko et al., 1997 ) and petroselinic acid (cis-6-octadecenoic acid) (Kaneko et al., 1992a ,b ). No trans-octadecenoic acid structure has been reported to date.

Elaidic acid (I) has an essentially linear alkyl chain, with the torsion angle between saturated C atoms close to 180° (Table 1). The C7—C8—C9—C10, C8—C9—C10—C11 and C9—C10—C11—C12 torsion angles are −118.8 (4), −179.9 (4) and 118.6 (4)°, respectively, resulting in the double bond being twisted across the mean direction of the alkyl chain in a skew′, trans, skew conformation. The C1–C18 distance is 21.393 (6) Å, comparable with that in fully extended stearic acid structures (21.6 Å; Malta et al., 1971; Kaneko et al., 1990, 1994b). This contrasts with the cis-octadecenoic acids, where the molecules are bent and the C1–C18 distance is reduced to between 17.8 and 19.7 Å (Abrahamsson & Ryderstedt-Nahringbauer, 1962; Kaneko et al., 1997, 1992a,b).

In the crystal structure of (I), molecules related by inversion centres are linked by O—H⋯O hydrogen bonds to form R₂²(8) dimers (Bernstein et al., 1995 ) typical of carboxylic acids (Table 2).

Figure 1
A view of (I)

, with displacement ellipsoids drawn at the 30% probability level.

Experimental

A commercial sample of (I) (Sigma, Poole, Dorset, UK) was re-crystallized from ethanol at room temperature. The crystals were composed of very thin stacked sheets which tended to be twisted. After many attempts, a crystal was found from which it was possible to obtain a data set.

Crystal data

C₁₈H₃₄O₂
M_r = 282.45
Monoclinic, C 2/c
a = 98.48 (2) Å
b = 4.9381 (3) Å
c = 7.1826 (8) Å
β = 92.570 (12)°
V = 3489.4 (8) Å³
Z = 8
D_x = 1.075 Mg m⁻³
Mo Kα radiation
Cell parameters from 3830 reflections
θ = 3.3–27.6°
μ = 0.07 mm⁻¹
T = 120 (2) K
Plate, colourless
0.20 × 0.18 × 0.01 mm

Data collection

Bruker Nonius KappaCCD area-detector diffractometer
φ and ω scans
Absorption correction: multi-scan(SADABS; Sheldrick, 2003 )T_min = 0.987, T_max = 0.999
17532 measured reflections
3830 independent reflections
1679 reflections with I > 2σ(I)
R_int = 0.150
θ_max = 27.6°
h = −126 → 126
k = −6 → 6
l = −9 → 9

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.102
wR(F²) = 0.256
S = 1.08
3830 reflections
182 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0744P)² + 7.8445P] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max = 0.001
Δρ_max = 0.41 e Å⁻³
Δρ_min = −0.35 e Å⁻³

Table 1
Selected torsion angles (°)

C1—C2—C3—C4	−170.7 (3)
C2—C3—C4—C5	177.0 (3)
C3—C4—C5—C6	−176.6 (3)
C4—C5—C6—C7	178.9 (3)
C5—C6—C7—C8	−179.1 (3)
C6—C7—C8—C9	−178.4 (3)
C7—C8—C9—C10	−118.8 (4)
C8—C9—C10—C11	−179.9 (4)
C9—C10—C11—C12	118.6 (4)
C10—C11—C12—C13	178.4 (3)
C11—C12—C13—C14	−179.8 (3)
C12—C13—C14—C15	179.9 (3)
C13—C14—C15—C16	179.8 (3)
C14—C15—C16—C17	−179.6 (3)
C15—C16—C17—C18	179.5 (3)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O2ⁱ	0.87	1.86	2.684 (3)	158
Symmetry code: (i) $[-x+{\script{3\over 2}}, -y+{\script{3\over 2}}, -z+1]$ .

H atoms were treated as riding, with C—H(aromatic) = 0.95 and C—H(CH₂) = 0.99 Å, with U_iso(H) = 1.2U_eq(C), C—H(methyl) = 0.98 Å, with U_iso(H) = 1.5U_eq(C), and O—H = 0.87 Å, with U_iso(H) = 1.5U_eq(O). The O-bound H atom was allowed to ride at its position as determined from a difference map. Although the best crystal was selected from many crystallization attempts, the higher than usual values for R, wR and R_int may be a result of the crystal quality. The possibilty that the crystal was twinned was investigated but this did not give any significant results.

Data collection: COLLECT (Nonius, 1998 ); cell refinement: DENZO (Otwinowski & Minor, 1997 ) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: OSCAIL (McArdle, 2003 ) and SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: OSCAIL and SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976 ) and PLATON (Spek, 2003 ); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536805033040/lh6524sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536805033040/lh6524Isup2.hkl

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: OSCAIL (McArdle, 2003) and SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: OSCAIL and SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).

trans-9-octadecenoic acid top

Crystal data top

C₁₈H₃₄O₂	F(000) = 1264
M_r = 282.45	D_x = 1.075 Mg m⁻³
Monoclinic, C2/c	Melting point: 318 K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 98.48 (2) Å	Cell parameters from 3830 reflections
b = 4.9381 (3) Å	θ = 3.3–27.6°
c = 7.1826 (8) Å	µ = 0.07 mm⁻¹
β = 92.570 (12)°	T = 120 K
V = 3489.4 (8) Å³	Plate, colourless
Z = 8	0.20 × 0.18 × 0.01 mm

Data collection top

Bruker Nonius KappaCCD area-detector diffractometer	3830 independent reflections
Radiation source: Bruker Nonius FR91 rotating anode	1679 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.150
Detector resolution: 9.091 pixels mm^-1	θ_max = 27.6°, θ_min = 3.3°
φ and ω scans	h = −126→126
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −6→6
T_min = 0.987, T_max = 0.999	l = −9→9
17532 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.102	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.256	H-atom parameters constrained
S = 1.08	w = 1/[σ²(F_o²) + (0.0744P)² + 7.8445P] where P = (F_o² + 2F_c²)/3
3830 reflections	(Δ/σ)_max = 0.001
182 parameters	Δρ_max = 0.41 e Å⁻³
0 restraints	Δρ_min = −0.35 e Å⁻³

Special details top

Experimental. The scale factors in the experimental table are calculated from the 'size' command in the SHELXL97 input file.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.73264 (3)	0.7933 (8)	0.6134 (6)	0.0228 (10)
O1	0.74261 (2)	0.9565 (6)	0.6713 (4)	0.0309 (8)
O2	0.73386 (2)	0.6167 (6)	0.4964 (4)	0.0248 (7)
C2	0.71969 (3)	0.8502 (8)	0.7109 (5)	0.0201 (10)
C3	0.70703 (3)	0.7093 (8)	0.6268 (6)	0.0205 (10)
C4	0.69400 (3)	0.8111 (8)	0.7115 (5)	0.0189 (9)
C5	0.68092 (3)	0.6865 (8)	0.6249 (6)	0.0209 (10)
C6	0.66795 (3)	0.8041 (8)	0.7042 (6)	0.0192 (9)
C7	0.65479 (3)	0.6840 (8)	0.6155 (6)	0.0217 (10)
C8	0.64192 (3)	0.8070 (8)	0.6941 (6)	0.0217 (10)
C9	0.62897 (3)	0.6835 (8)	0.6108 (5)	0.0228 (10)
C10	0.61931 (3)	0.8140 (8)	0.5146 (5)	0.0218 (10)
C11	0.60645 (3)	0.6909 (8)	0.4322 (6)	0.0245 (10)
C12	0.59348 (3)	0.8106 (8)	0.5097 (5)	0.0193 (9)
C13	0.58035 (3)	0.6919 (8)	0.4225 (6)	0.0218 (10)
C14	0.56738 (3)	0.8113 (8)	0.4988 (6)	0.0208 (10)
C15	0.55429 (3)	0.6890 (8)	0.4087 (6)	0.0223 (10)
C16	0.54127 (3)	0.8076 (8)	0.4853 (6)	0.0224 (10)
C17	0.52827 (3)	0.6812 (9)	0.3945 (6)	0.0282 (11)
C18	0.51520 (3)	0.7981 (9)	0.4725 (7)	0.0360 (12)
H1	0.7506	0.9756	0.6267	0.046*
H2A	0.7181	1.0481	0.7094	0.024*
H2B	0.7210	0.7940	0.8428	0.024*
H3A	0.7079	0.5117	0.6478	0.025*
H3B	0.7065	0.7411	0.4906	0.025*
H4A	0.6935	1.0102	0.6969	0.023*
H4B	0.6945	0.7711	0.8467	0.023*
H5A	0.6811	0.4884	0.6464	0.025*
H5B	0.6807	0.7170	0.4885	0.025*
H6A	0.6679	1.0026	0.6849	0.023*
H6B	0.6681	0.7704	0.8402	0.023*
H7A	0.6546	0.7151	0.4793	0.026*
H7B	0.6548	0.4860	0.6367	0.026*
H8A	0.6422	0.7806	0.8309	0.026*
H8B	0.6418	1.0043	0.6697	0.026*
H9	0.6277	0.4949	0.6294	0.027*
H10	0.6206	1.0025	0.4956	0.026*
H11A	0.6066	0.4935	0.4565	0.029*
H11B	0.6062	0.7173	0.2955	0.029*
H12A	0.5936	0.7795	0.6459	0.023*
H12B	0.5935	1.0088	0.4888	0.023*
H13A	0.5804	0.4938	0.4437	0.026*
H13B	0.5802	0.7224	0.2862	0.026*
H14A	0.5673	1.0094	0.4776	0.025*
H14B	0.5675	0.7802	0.6350	0.025*
H15A	0.5542	0.7206	0.2725	0.027*
H15B	0.5544	0.4908	0.4295	0.027*
H16A	0.5411	1.0055	0.4635	0.027*
H16B	0.5414	0.7770	0.6216	0.027*
H17A	0.5282	0.7132	0.2583	0.034*
H17B	0.5285	0.4830	0.4152	0.034*
H18A	0.5151	0.7603	0.6063	0.054*
H18B	0.5073	0.7141	0.4086	0.054*
H18C	0.5149	0.9943	0.4521	0.054*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0142 (16)	0.022 (2)	0.032 (3)	0.0038 (16)	−0.0035 (17)	0.005 (2)
O1	0.0171 (11)	0.0333 (19)	0.042 (2)	−0.0079 (12)	0.0022 (12)	−0.0123 (15)
O2	0.0219 (12)	0.0276 (18)	0.0251 (18)	−0.0011 (12)	0.0008 (11)	−0.0047 (15)
C2	0.0194 (16)	0.022 (2)	0.019 (3)	0.0035 (16)	−0.0021 (15)	−0.0017 (19)
C3	0.0166 (16)	0.020 (2)	0.025 (3)	0.0031 (15)	−0.0015 (16)	0.0035 (19)
C4	0.0191 (16)	0.019 (2)	0.019 (2)	0.0016 (15)	0.0015 (16)	−0.0005 (18)
C5	0.0183 (16)	0.019 (2)	0.025 (3)	−0.0030 (16)	−0.0059 (16)	0.0025 (19)
C6	0.0163 (16)	0.021 (2)	0.020 (3)	−0.0015 (15)	0.0024 (15)	0.0008 (19)
C7	0.0201 (16)	0.025 (2)	0.020 (3)	−0.0024 (16)	−0.0050 (16)	0.0019 (19)
C8	0.0194 (17)	0.028 (2)	0.018 (3)	−0.0018 (16)	0.0021 (16)	0.0018 (19)
C9	0.0232 (17)	0.024 (3)	0.022 (3)	−0.0005 (17)	0.0028 (17)	−0.001 (2)
C10	0.0154 (16)	0.023 (2)	0.026 (3)	−0.0026 (16)	0.0004 (16)	0.001 (2)
C11	0.0197 (17)	0.026 (2)	0.027 (3)	−0.0010 (16)	−0.0068 (17)	0.001 (2)
C12	0.0187 (16)	0.025 (2)	0.014 (2)	0.0003 (16)	−0.0002 (15)	0.0013 (19)
C13	0.0193 (17)	0.026 (2)	0.020 (3)	−0.0018 (16)	−0.0023 (16)	0.0005 (19)
C14	0.0209 (17)	0.021 (2)	0.020 (3)	0.0010 (16)	−0.0022 (16)	0.0010 (19)
C15	0.0205 (17)	0.025 (2)	0.021 (3)	0.0001 (16)	−0.0032 (16)	−0.002 (2)
C16	0.0232 (17)	0.021 (2)	0.023 (3)	0.0019 (16)	−0.0003 (17)	−0.0014 (19)
C17	0.0207 (17)	0.037 (3)	0.027 (3)	−0.0025 (17)	−0.0039 (17)	0.001 (2)
C18	0.0263 (19)	0.040 (3)	0.041 (3)	−0.0003 (19)	−0.0041 (19)	0.002 (2)

Geometric parameters (Å, º) top

C1—O2	1.221 (5)	C10—C11	1.502 (4)
C1—O1	1.323 (4)	C10—H10	0.95
C1—C2	1.508 (5)	C11—C12	1.535 (5)
O1—H1	0.8642	C11—H11A	0.99
C2—C3	1.528 (4)	C11—H11B	0.99
C2—H2A	0.99	C12—C13	1.527 (4)
C2—H2B	0.99	C12—H12A	0.99
C3—C4	1.530 (5)	C12—H12B	0.99
C3—H3A	0.99	C13—C14	1.530 (5)
C3—H3B	0.99	C13—H13A	0.99
C4—C5	1.534 (4)	C13—H13B	0.99
C4—H4A	0.99	C14—C15	1.540 (4)
C4—H4B	0.99	C14—H14A	0.99
C5—C6	1.536 (5)	C14—H14B	0.99
C5—H5A	0.99	C15—C16	1.534 (5)
C5—H5B	0.99	C15—H15A	0.99
C6—C7	1.537 (4)	C15—H15B	0.99
C6—H6A	0.99	C16—C17	1.542 (4)
C6—H6B	0.99	C16—H16A	0.99
C7—C8	1.536 (5)	C16—H16B	0.99
C7—H7A	0.99	C17—C18	1.540 (5)
C7—H7B	0.99	C17—H17A	0.99
C8—C9	1.512 (4)	C17—H17B	0.99
C8—H8A	0.99	C18—H18A	0.98
C8—H8B	0.99	C18—H18B	0.98
C9—C10	1.318 (5)	C18—H18C	0.98
C9—H9	0.95

O2—C1—O1	123.9 (3)	C9—C10—H10	117.1
O2—C1—C2	124.3 (3)	C11—C10—H10	117.1
O1—C1—C2	111.8 (4)	C10—C11—C12	113.7 (3)
C1—O1—H1	128.4	C10—C11—H11A	108.8
C1—C2—C3	115.1 (3)	C12—C11—H11A	108.8
C1—C2—H2A	108.5	C10—C11—H11B	108.8
C3—C2—H2A	108.5	C12—C11—H11B	108.8
C1—C2—H2B	108.5	H11A—C11—H11B	107.7
C3—C2—H2B	108.5	C13—C12—C11	114.0 (3)
H2A—C2—H2B	107.5	C13—C12—H12A	108.8
C2—C3—C4	112.2 (3)	C11—C12—H12A	108.8
C2—C3—H3A	109.2	C13—C12—H12B	108.8
C4—C3—H3A	109.2	C11—C12—H12B	108.8
C2—C3—H3B	109.2	H12A—C12—H12B	107.7
C4—C3—H3B	109.2	C12—C13—C14	114.2 (3)
H3A—C3—H3B	107.9	C12—C13—H13A	108.7
C3—C4—C5	114.3 (3)	C14—C13—H13A	108.7
C3—C4—H4A	108.7	C12—C13—H13B	108.7
C5—C4—H4A	108.7	C14—C13—H13B	108.7
C3—C4—H4B	108.7	H13A—C13—H13B	107.6
C5—C4—H4B	108.7	C13—C14—C15	113.3 (3)
H4A—C4—H4B	107.6	C13—C14—H14A	108.9
C4—C5—C6	113.3 (3)	C15—C14—H14A	108.9
C4—C5—H5A	108.9	C13—C14—H14B	108.9
C6—C5—H5A	108.9	C15—C14—H14B	108.9
C4—C5—H5B	108.9	H14A—C14—H14B	107.7
C6—C5—H5B	108.9	C16—C15—C14	113.4 (3)
H5A—C5—H5B	107.7	C16—C15—H15A	108.9
C5—C6—C7	113.6 (3)	C14—C15—H15A	108.9
C5—C6—H6A	108.8	C16—C15—H15B	108.9
C7—C6—H6A	108.8	C14—C15—H15B	108.9
C5—C6—H6B	108.8	H15A—C15—H15B	107.7
C7—C6—H6B	108.8	C15—C16—C17	112.6 (3)
H6A—C6—H6B	107.7	C15—C16—H16A	109.1
C8—C7—C6	112.9 (3)	C17—C16—H16A	109.1
C8—C7—H7A	109.0	C15—C16—H16B	109.1
C6—C7—H7A	109.0	C17—C16—H16B	109.1
C8—C7—H7B	109.0	H16A—C16—H16B	107.8
C6—C7—H7B	109.0	C18—C17—C16	112.7 (3)
H7A—C7—H7B	107.8	C18—C17—H17A	109.0
C9—C8—C7	113.0 (3)	C16—C17—H17A	109.0
C9—C8—H8A	109.0	C18—C17—H17B	109.0
C7—C8—H8A	109.0	C16—C17—H17B	109.0
C9—C8—H8B	109.0	H17A—C17—H17B	107.8
C7—C8—H8B	109.0	C17—C18—H18A	109.5
H8A—C8—H8B	107.8	C17—C18—H18B	109.5
C10—C9—C8	125.9 (4)	H18A—C18—H18B	109.5
C10—C9—H9	117.1	C17—C18—H18C	109.5
C8—C9—H9	117.1	H18A—C18—H18C	109.5
C9—C10—C11	125.7 (4)	H18B—C18—H18C	109.5

O2—C1—C2—C3	−11.8 (6)	C8—C9—C10—C11	−179.9 (4)
O1—C1—C2—C3	168.8 (3)	C9—C10—C11—C12	118.6 (4)
C1—C2—C3—C4	−170.7 (3)	C10—C11—C12—C13	178.4 (3)
C2—C3—C4—C5	177.0 (3)	C11—C12—C13—C14	−179.8 (3)
C3—C4—C5—C6	−176.6 (3)	C12—C13—C14—C15	179.9 (3)
C4—C5—C6—C7	178.9 (3)	C13—C14—C15—C16	179.8 (3)
C5—C6—C7—C8	−179.1 (3)	C14—C15—C16—C17	−179.6 (3)
C6—C7—C8—C9	−178.4 (3)	C15—C16—C17—C18	179.5 (3)
C7—C8—C9—C10	−118.8 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2ⁱ	0.87	1.86	2.684 (3)	158

Symmetry code: (i) −x+3/2, −y+3/2, −z+1.

Acknowledgements

The X-ray data were collected at the EPSRC X-ray Crystallographic Service, University of Southampton, England. The Scottish Crop Research Institute receives grant-in-aid from the Scottish Executive Environmental and Rural Affairs Department.

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