2-Fluoro-4-(methoxycarbonyl)benzoic acid

In the crystal of the title compound, C9H7FO4, classical carboxylate inversion dimers are linked by pairs of O—H⋯O hydrogen bonds. The packing is consolidated by C—H⋯F and C—H⋯O interactions. The benzene ring and the methoxycarbonyl group are nearly coplanar, with a dihedral angle of 1.5 (3)° between them, whereas the carboxyl group has a dihedral angle of 20.2 (4)° with respect to the benzene ring.

In the crystal of the title compound, C 9 H 7 FO 4 , classical carboxylate inversion dimers are linked by pairs of O-HÁ Á ÁO hydrogen bonds. The packing is consolidated by C-HÁ Á ÁF and C-HÁ Á ÁO interactions. The benzene ring and the methoxycarbonyl group are nearly coplanar, with a dihedral angle of 1.5 (3) between them, whereas the carboxyl group has a dihedral angle of 20.2 (4) with respect to the benzene ring.

Comment
The title compound, 4-(methoxycarbonyl)-2-fluorobenzoic acid, has recently been used to prepare novel diazepinylbenzoic acid retinoid-X-receptor antagonists (Jiang et al., 2008;Sakaki et al., 2007) as potential oral anti-obesity and anti-diabetic treatments as well as novel retinoid-X-receptor agonists with potential to treat various human cancers. Thus, the X-ray diffraction data of the present study confirms the fluorine locus for 4-(methoxycarbonyl)-2-fluorobenzoic acid.
The structure consists of sheets parallel to (212) stabilized by six intermolecular hydrogen interactions per molecule as shown in Table 1. The benzene ring and the methoxycarbonyl group are essentially coplanar as shown by the 1.51 (25)°d ihedral angle between the two planes. However, the carboxylic acid is not coplanar with the benzene ring, as shown by the 20.18 (36)° dihedral angle between those two planes.

Refinement
H atoms were placed geometrically and allowed to refine as atoms riding on their bonding partners. The hydrogen was placed on the carboxylic acid based on the longer of the carboxylic acid carbon-oxygen bonds.
supplementary materials sup-2 Figures   Fig. 1. Labeled thermal ellipsoid plot of (1) shown at the 50% probability level for all non-H atoms.   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.
H atoms were placed geometrically and allowed to refine as atoms riding on their bonding partners. The hydrogen was placed on the carboxylic acid based on the longer of the carboxylic acid carbon-oxygen bonds.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq F1 0.4739 (