Redetermination of 2,6-dimethoxy­benzoic acid

Gustavo Portalone

doi:10.1107/S1600536809001408

. 2009 Jan 17;65(Pt 2):o327–o328. doi: 10.1107/S1600536809001408

Redetermination of 2,6-dimethoxybenzoic acid

Gustavo Portalone ^a,^*

PMCID: PMC2968263 PMID: 21581932

Abstract

The crystal structure of the title compound, C₉H₁₀O₄, was first reported by Swaminathan, Vimala & Lotter [Acta Cryst. (1976), B32, 1897–1900]. It has been re-examined, improving the precision of the derived geometric parameters. The asymmetric unit comprises a non-planar independent molecule, as the methoxy substituents force the carboxy group to be twisted away from the plane of the aromatic ring by 56.12 (9)°. Due to the antiplanar conformation adopted by the OH group, the molecular components do not form the conventional dimeric units, but are associated in the crystal in chains stabilized by linear O—H⋯O hydrogen bonds, involving the OH groups and the carbonyl O atoms, which form C(3) motifs.

Related literature

For previous structure determinations, see: Swaminathan et al. (1976 ▶); Bryan & White (1982 ▶). For related literature, see: Gopalakrishna & Cartz, 1972 ▶; Leiserowitz, 1976 ▶; Byriel et al., 1991 ▶; Chen et al., 2007 ▶. For computation of ring patterns formed by hydrogen bonds in crystal structures, see: Etter et al. (1990 ▶); Bernstein et al. (1995 ▶); Motherwell et al. (1999 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

C₉H₁₀O₄
M _r = 182.17
Orthorhombic,
a = 7.12255 (13) Å
b = 8.92296 (15) Å
c = 13.79430 (18) Å
V = 876.69 (2) Å³
Z = 4
Mo Kα radiation
μ = 0.11 mm⁻¹
T = 298 (2) K
0.12 × 0.10 × 0.10 mm

Data collection

Oxford Diffraction Xcalibur S CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006 ▶) T _min = 0.967, T _max = 0.999
234729 measured reflections
1246 independent reflections
1241 reflections with I > 2σ(I)
R _int = 0.039

Refinement

R[F ² > 2σ(F ²)] = 0.042
wR(F ²) = 0.110
S = 1.25
1246 reflections
129 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.17 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2006 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809001408/kp2203sup1.cif

e-65-0o327-sup1.cif^{(15.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809001408/kp2203Isup2.hkl

e-65-0o327-Isup2.hkl^{(60.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2⋯O1ⁱ	0.87 (4)	1.82 (4)	2.681 (2)	172 (4)

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Symmetry code: (i) Inline graphic .

Acknowledgments

We thank MIUR (Rome) for 2006 financial support of the project ‘X-ray diffractometry and spectrometry’.

supplementary crystallographic information

Comment

2,6-Dimethoxybenzoic acid was determined some 30 years ago (Swaminathan et al., 1976) but the final refinement was carried only to R=0.15 and no atomic coordinates were provided. Subsequently, a new X-ray structure determination was reported (Bryan & White, 1982). In this study, 775 unique reflections were collected at ambient temperature on an automatic diffractometer using Cu Kα radiation. Data were corrected for Lp effects, but not for absorption [µ(Cu Kα)= 94 mm^-1]. 708 reflections having values significantly above background were used in the block-diagonal least-squares refinement. The final calculations, carried out on a fairly small data set, led to R = 0.035 for 158 refined parameters, a data-to-parameter ratio of 4.5, the maximum shift-to-error in the final cycle being equal to 1/4, and standard deviations of 0.005Å in C—C bond lengths and 0.4° in bond angles.

The asymmetric unit of (I) comprises a non-planar independent molecule, as the methoxy substituents force the carboxy group to be twisted away from the plane of the aromatic ring by 56.12 (9)° (Fig. 1). The values of bond lengths and bond angles are consistent with that reported in the previous determination (Bryan & White, 1982) with the exception of the geometrical parameters of the carboxy group. Analysis of the crystal packing of (I), (Table 1, Fig. 2) shows that the molecular components do not form the conventional dimeric units observed in monocarboylic acids (Leiserowitz, 1976). The structure is stabilized by intermolecular O—H···O interactions of descriptor C(3) (Etter et al., 1990; Bernstein et al., 1995; Motherwell et al., 1999) (Table 1, Fig. 2) between the OH moieties and the carbonyl O atom (O1ⁱ) [symmetry code: (i) -x, y - 1/2, -z + 1/2] which link the molecules into endless chains approximately parallel to b. A search of the Cambridge Structural Database (version 5.29; Allen, 2002) for crystal structures containing the o-methoxy benzoic acid residue yields only three structures having the OH group in the unusual antiplanar conformation (Gopalakrishna & Cartz, 1972; Byriel et al., 1991; Chen et al., 2007). For these compounds, the antiplanar conformation is favoured by the formation of intramolecular hydrogen bonding.

Experimental

2,6-Dimethoxybenzoic acid (0.1 mmol, Sigma Aldrich at 99% purity) was dissolved in ethanol (95%, 9 mL) and gently heated under reflux for 1 h. After cooling the solution to an ambient temperature, crystals suitable for single-crystal X-ray diffraction were grown by slow evaporation of the solvent after two days.