Octa­decane-1,18-diol

The skeleton of the title mol­ecule, C₁₈H₃₈O₂, is all-trans and the mol­ecules aggregate to form a layer structure along the c axis as in a smectic C liquid crystal. The inclination angle of the long axis of the mol­ecule to the layer plane is the same in each layer, but the direction of the long axis is opposite in alternate layers. These features are very similar to those of the homologues with an even number of C atoms, but different from those with an odd number.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.045
• wR factor = 0.065
• Data-to-parameter ratio = 10.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Crystal structures of long-chain compounds such as n-alkanes (Müller, 1928) and n-higher primary alcohols (e.g. Watanabe, 1961; Seto, 1962), have been studied by many researchers from the viewpoint of basic polymer science. According to those results, the compounds have a simple straight hydrocarbon chain as a skeleton and the molecular shape can be regarded as a rod-like, which is one of the typical features of liquid crystal molecules. In addition, some long-chain compounds construct a layer structure in the crystal state, which is similar to that of a smectic phase of liquid crystals. Therefore, these compounds have been studied from a structural point of view as models for smectic liquid crystals.

We have already reported molecular and crystal structure of α,ω-alkanediols containing from 10 through 17 and 21 C atoms, these were investigated by Nakamura and co-workers: 1,10-decanediol (Nakamura & Sato, 1999a), 1,11-undecanediol (Nakamura et al., 1999), 1,12-dodecanediol (Nakamura & Setodoi, 1997), 1,13-tridecanediol (Nakamura et al., 1997), 1,14-tetradecanediol (Nakamura & Sato, 1999b), 1,15-pentadecanediol (Nakamura et al., 2000), 1,16-hexadecanediol (Nakamura & Yamamoto, 1994), 1,17-heptadecanediol (Nakamura et al., 2001) and 1,21-henicosanediol (Nakamura et al., 2000a). The results showed a clear distinction in the structures between the compounds with an even number of C atoms and those with an odd number of C atoms. In the α,ω-alkanediols with even number of C atoms, the hydroxyl groups located at both ends of a hydrocarbon skeleton showed an all-trans conformation with respect to the skeleton. These molecules were arranged making layers in a herring-bone fashion, just like the chiral smectic C liquid crystals. On the other hand, in the α,ω-alkanediols with an odd number of C atoms, one hydroxyl group had gauche conformation with respect to the hydrocarbon skeleton, whereas another hydroxyl group had trans conformation. In this case, molecules made a layer structure which was very similar to that of the smectic A liquid crystals. In addition, phase transition of α,ω-alkanediols from C13 through C24 was studied by means of a powder X-ray diffraction method and a linear relation of the longest axis of lattice constant versus number of C atoms was reported (Ogawa & Nakamura, 1999).

In the crystal structure of 1,18-octadecanediol, (I), shown in Fig. 1, an all-trans conformation was observed not only in the hydrocarbon skeleton but also in both terminal hydroxyl groups. The molecule is centrosymmetric and forms a layer structure stacked along c axis. The inclination angle of the long axis of the molecule to the layer plane is equal in each layer, but the direction of the long axis of the molecule is opposite in alternate layers because of an existence of a twofold screw axis parallel to b. Such herring-bone structures can be regarded as a model structure of chiral smectic C liquid crystals. These features are very similar to those of 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol and 1,16-hexadecanediol. Average value of inclination angles of above compounds was about 56° as found in the present structure. These molecules form interlayer hydrogen bonds, as shown in Fig. 2, with the interlayer hydrogen-bonding distance O1···O1ⁱ = 2.843 (2) Å [symmetry code: (i) 3 - x, 0.5 + y, 0.5 - z]. This value is in good agreement these of other α,ω-alkanediols with an even number of C atoms.

S2. Experimental

According to the conventional method, the title compound, (I), was synthesized from commercially available octadecanedioic acid (Tokyo Kasei Kogyo Co. Ltd) by esterification and reduction with LiAlH₄. The single-crystal used for analysis was grown by very slow evaporation from a solution in a mixed solvent system comprising methanol, ethyl acetate and dimetylbenzene (1:1:3 ratio).

S3. Refinement

All H atoms, including hydroxyl H atoms, were fixed in idealized positions.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1992); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 1995); program(s) used to solve structure: SAPI91 (Fan, 1991); program(s) used to refine structure: TEXSAN; software used to prepare material for publication: TEXSAN.

Figures

	Fig. 1. An ORTEPII (Johnson, 1976) view of the title molecule showing the crystallographic numbering scheme. Displacement ellipsoids are drawn at 50° probability level.
	Fig. 2. The bc-projection of the crystal structure; dotted lines indicate the hydrogen bonds.

(I)

Crystal data

C18H38O2	F(000) = 324
Mr = 286.50	Dx = 1.047 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.5418 Å
a = 4.998 (2) Å	Cell parameters from 24 reflections
b = 5.220 (2) Å	θ = 9.3–20.1°
c = 34.853 (2) Å	µ = 0.50 mm^−1
β = 92.04 (2)°	T = 298 K
V = 908.8 (5) Å^3	Plate, colorless
Z = 2	0.40 × 0.20 × 0.02 mm

Data collection

Rigaku AFC-5R diffractometer	991 reflections with I > 2σ(I)
Radiation source: Rigaku rotating anode	Rint = 0.025
Graphite monochromator	θmax = 70.5°, θmin = 2.5°
ω–2θ scans	h = −2→6
Absorption correction: ψ scans (North et al., 1968)	k = 0→5
Tmin = 0.929, Tmax = 1	l = −42→42
2843 measured reflections	3 standard reflections every 150 reflections
1802 independent reflections	intensity decay: 2.6%

Refinement

Refinement on F	0 restraints
Least-squares matrix: full	0 constraints
R[F^2 > 2σ(F^2)] = 0.045	H-atom parameters not refined
wR(F^2) = 0.065	w = 1/[σ^2(Fo) + 0.00053|Fo|^2]
S = 1.67	(Δ/σ)max < 0.001
991 reflections	Δρmax = 0.12 e Å^−3
91 parameters	Δρmin = −0.11 e Å^−3

Special details

Experimental. none

Geometry. none

Refinement. None

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	1.4119 (3)	−0.4953 (3)	0.23943 (4)	0.0802 (5)
C1	1.2271 (4)	−0.5358 (4)	0.20834 (5)	0.0599 (6)
C2	1.1288 (4)	−0.2830 (4)	0.19336 (5)	0.0540 (5)
C3	0.9330 (4)	−0.3089 (4)	0.15912 (5)	0.0517 (5)
C4	0.8304 (4)	−0.0540 (4)	0.14358 (5)	0.0514 (5)
C5	0.6396 (4)	−0.0809 (4)	0.10891 (5)	0.0513 (5)
C6	0.5365 (4)	0.1724 (4)	0.09318 (5)	0.0500 (5)
C7	0.3465 (4)	0.1468 (4)	0.05827 (5)	0.0500 (5)
C8	0.2426 (4)	0.4007 (4)	0.04263 (5)	0.0501 (5)
C9	0.0519 (4)	0.3726 (4)	0.00781 (5)	0.0496 (6)
H0	1.4782	−0.6526	0.2493	0.0916*
H1a	1.3082	−0.6345	0.1882	0.0799*
H1b	1.0770	−0.6387	0.2167	0.0799*
H2a	1.2796	−0.1823	0.1854	0.0655*
H2b	1.0437	−0.1900	0.2132	0.0655*
H3a	1.0188	−0.3972	0.1390	0.0649*
H3b	0.7832	−0.4075	0.1667	0.0649*
H4a	0.9802	0.0478	0.1364	0.0598*
H4b	0.7398	0.0337	0.1633	0.0598*
H5a	0.7313	−0.1706	0.0889	0.0631*
H5b	0.4911	−0.1860	0.1158	0.0631*
H6a	0.6855	0.2788	0.0862	0.0601*
H6b	0.4449	0.2630	0.1130	0.0601*
H7a	0.4376	0.0570	0.0384	0.0621*
H7b	0.1970	0.0410	0.0652	0.0621*
H8a	0.3905	0.5056	0.0355	0.0607*
H8b	0.1502	0.4899	0.0624	0.0607*
H9a	0.1427	0.2828	−0.0120	0.0594*
H9b	−0.0979	0.2686	0.0149	0.0594*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.096 (1)	0.0647 (10)	0.0759 (9)	−0.0011 (8)	−0.0557 (8)	0.0046 (8)
C1	0.068 (1)	0.056 (1)	0.0534 (10)	−0.0013 (10)	−0.0282 (9)	0.0024 (9)
C2	0.059 (1)	0.056 (1)	0.0466 (9)	0.0017 (9)	−0.0176 (8)	−0.0008 (8)
C3	0.054 (1)	0.052 (1)	0.0479 (9)	−0.0045 (9)	−0.0158 (8)	0.0034 (8)
C4	0.0525 (10)	0.051 (1)	0.0490 (9)	−0.0041 (9)	−0.0152 (8)	0.0031 (8)
C5	0.054 (1)	0.051 (1)	0.0473 (9)	−0.0007 (9)	−0.0168 (8)	0.0010 (8)
C6	0.054 (1)	0.048 (1)	0.0471 (10)	−0.0008 (8)	−0.0163 (8)	0.0002 (8)
C7	0.054 (1)	0.049 (1)	0.0462 (9)	−0.0031 (9)	−0.0148 (8)	0.0011 (8)
C8	0.053 (1)	0.049 (1)	0.0475 (10)	−0.0032 (8)	−0.0155 (8)	0.0020 (7)
C9	0.055 (1)	0.049 (1)	0.0442 (10)	−0.0019 (8)	−0.0159 (8)	0.0026 (7)

Geometric parameters (Å, º)

O1—C1	1.414 (2)	C5—C6	1.515 (2)
C1—C2	1.496 (3)	C6—C7	1.523 (2)
C2—C3	1.522 (2)	C7—C8	1.518 (3)
C3—C4	1.519 (2)	C8—C9	1.523 (2)
C4—C5	1.519 (2)	C9—C9^i	1.521 (4)
O1···O1^ii	2.843 (2)	O1···C1^ii	3.477 (2)
O1···O1^iii	2.843 (2)	O1···C2^iii	3.554 (2)
O1—C1—C2	109.4 (1)	C5—C6—C7	114.0 (1)
C1—C2—C3	112.9 (2)	C6—C7—C8	114.0 (2)
C2—C3—C4	113.7 (2)	C7—C8—C9	113.5 (1)
C3—C4—C5	113.4 (1)	C8—C9—C9^i	113.4 (2)
C4—C5—C6	113.8 (2)

Symmetry codes: (i) −x, −y+1, −z; (ii) −x+3, y+1/2, −z+1/2; (iii) −x+3, y−1/2, −z+1/2.