4-(4-Fluorophenoxy)benzoic acid

In the title compound, C13H9FO3, the dihedral angle between the two benzene rings is 70.99 (5)°. In the crystal structure, molecules are linked into dimers by centrosymmetric O—H⋯O interactions, generating R 2 2(8) ring motifs. These dimers are linked into a two-dimensional array, parallel to the ab plane, by two different C—H⋯O interactions. A weak C—H⋯π interactions is also present.

In the title compound, C 13 H 9 FO 3 , the dihedral angle between the two benzene rings is 70.99 (5) . In the crystal structure, molecules are linked into dimers by centrosymmetric O-HÁ Á ÁO interactions, generating R 2 2 (8) ring motifs. These dimers are linked into a two-dimensional array, parallel to the ab plane, by two different C-HÁ Á ÁO interactions. A weak C-HÁ Á Á interactions is also present.

Comment
Phenoxy benzoic acids and its derivatives are known for their herbicidal and plant growth-regulating activities (Forster et al., 1989). These compounds are also used in the synthesis of various thiadiazoles and oxadiazole derivatives which show excellent anti-bacterial activity (Holla et al., 2003).The title compound, (I), which is used for peripheral neuropathic pain treatment, is a potent blocker of neuronal voltage-gated sodium channels that interacts selectively with inactivated states as opposed to resting states of the channels (Ramu et al., 2000). Fig. 1, the two benzene rings are inclined to one another, with dihedral angle of 70.99 (5)°. In the crystal structure ( Fig. 2), the molecules are linked into dimers by centrosymmetric O2-H1O2···O3 interactions (Table 1) to generate R 2 2 (8) ring motifs. These dimers are linked into a 2-D array, parallel to the ab plane, by intermolecular C-H···O interactions ( Table   1). The crystal structure is further stabilized by weak C2-H2A···Cg2 (Table 1) and π···π interactions involving the C1-C6 benzene rings (centroid Cg1) [Cg1···Cg1 = 3.6427 (6)°; symmetry code: 1-x, 2-y, 1-z].
Experimental 4-Bromo-methylbenzoate (0.760 g, 3.57 mmol), sodium carbonate (0.750 g, 7.00 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.400 g, 0.350 mmol) were added to a stirred solution of 4-fluorobenzene boronic acid (0.500 g, 3.57 mmol) in toluene and water (1:1) (20 ml). The reaction mixture was heated at reflux for 8 h; TLC indicated completion of reaction. Sodium hydroxide (0.284 g, 7.00 mmol) was added and stirring was continued for further 1 h. Mass analysis of crude reaction mixture shows the formation of desired compound. The reaction mixture was acidified to pH 3, extracted with ethylacetate and dried. The concentrated residue was purified by column chromatography to yield the pure product, which was recrystallized using hot dichloromethane to yield single crystals. The yield was 0.400 g, 50 %. M.p. 448-450 K.

Refinement
All the H atoms were located from difference Fourier map and allowed to refine freely [range of C-H = 0.959 (15) -0.981 (15) Å]. Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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 > 2sigma(F 2 ) is used only for calculating R-factors(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.