4-Bromo-1H-pyrrole-2-carboxylic acid

In the title compound, C5H4BrNO2, the non-H atoms of the pyrrole ring and the Br atom are approximately coplanar, with an r.m.s. deviation from the best fit plane of 0.025 (6) Å;. The dihedral angle between the plane of the carboxy group and this plane is 14.1 (2)°. In the crystal, O—H⋯O hydrogen bonds link the molecules together, forming corrugated sheets parallel to the bc plane.

In the title compound, C 5 H 4 BrNO 2 , the non-H atoms of the pyrrole ring and the Br atom are approximately coplanar, with an r.m.s. deviation from the best fit plane of 0.025 (6) Å ;. The dihedral angle between the plane of the carboxy group and this plane is 14.1 (2) . In the crystal, O-HÁ Á ÁO hydrogen bonds link the molecules together, forming corrugated sheets parallel to the bc plane.
In the title molecule, bond lengths and angles are unexceptional. The non-H atoms of the pyrrole ring and Br atom are approximately coplanar (plane 1), with r.m.s. deviation from the best fit plane of 0.025 (6)°, the dihedral angle between the carboxy plane and Plane 1 is 14.1 (2)°. The OH hydrogen atom is disordered over two positions (shown as in Fig. 1), which form weak intermolecular O2-H2···O1 hydrogen bonds respectively (Table 1). In the crystal, the above hydrogen bonds link the molecules into corrugated sheets parallel to the bc plane (shown as in Fig. 2 and Fig. 3).

Experimental
The methyl 4-bromopyrrole-2-carbonylaminoacetate (1.30 g, 5 mmol) and potassium carbonate (1.38 g, 10 mmol) were added to acetonitrile (20 ml), the mixture was stirred at reflux for 24 h. After the reaction mixture was cooled and filtered, the filtrate was evaporated in vacuo, and then the residue was chromatographed over Si gel 60 using EtOAc-petroleum ether (1:2.5) as eluting solvent and the title compound (I) was obtained (55.2% yield). Light yellow monoclinic crystals suitable for X-ray analysis (m.p. 424 K) grew over a period of one week when the EtOH solution of I was exposed to the air at room temperature.

Refinement
All non-H atoms were refined with anisotropic displacement parameters. The H atoms except the H(OH) were positioned geometrically[C-H = 0.93 Å for CH, and N-H = 0.86 Å] and refined using a riding model, with U iso = 1.2U eq of the parent atom. The H atoms attached to hydroxy O atoms were found automatically.

Computing details
Data collection: CrysAlis PRO (Oxford Diffraction, 2010); cell refinement: CrysAlis PRO (Oxford Diffraction, 2010); data reduction: CrysAlis PRO (Oxford Diffraction, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).  The molecular structure of the title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.   sheet formed by weak hydrogen bonds (dashed lines). 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 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.

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