2-Hydroxy-5-nitrobenzaldehyde

The title compound, C7H5NO4, is essentially planar, with a maximum deviation from the mean plane of 0.0116 (11) Å for the hydroxy O atom. The molecular and crystal structure are stabilized by intra- and intermolecular interactions. An intramolecular O—H⋯O hydrogen bond generates a six-membered ring, producing an S(6) ring motif. The C—H⋯O interactions result in the formation of C(5) chains and R 2 2(8) rings forming an approximately planar network parallel to (10). These planes are interconnected through π–π interactions [centroid–centroid distance 3.582 (2) Å].

The title compound, C 7 H 5 NO 4 , is essentially planar, with a maximum deviation from the mean plane of 0.0116 (11) Å for the hydroxy O atom. The molecular and crystal structure are stabilized by intra-and intermolecular interactions. An intramolecular O-HÁ Á ÁO hydrogen bond generates a sixmembered ring, producing an S(6) ring motif. The C-HÁ Á ÁO interactions result in the formation of C(5) chains and R 2 2 (8) rings forming an approximately planar network parallel to (101). These planes are interconnected throughinteractions [centroid-centroid distance 3.582 (2) Å ].

Comment
Nitroaromatics are widely used either as materials or as intermediates in explosives, dyestuffs, pesticides and organic synthesis (Yan et al., 2006). Nitroaromatics occur as industrial wastes and direct pollutants in the environment, and are relatively soluble in water and detectable in rivers, ponds and soil (Yan et al., 2006;Soojhawon et al., 2005). Morover, aromatic compounds with multiple nitro substituents are known to be resistant to electrophilic attack by oxygenases (Halas et al., 1983).
In the title compound (I, Fig. 1), the molecule is essentially planar with a maximum deviation from the mean plane of 0.0116 (11) Å for atom O3. The bond lengths and angles in (I) have normal values, and are comparable with those in the related structures (Rizal et al., 2008;Garden et al., 2004). The dihedral angle between the aromatic ring and the nitro group is 3.83 (3)°.

Experimental
The commercially available compound (Acros Organics) was recrystallized from ethanol.

Refinement
C-bound H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). The position of the H3A atom was obtained from a difference map of the electron density in the unit-cell and its coordinates were refined freely with U iso (H) = 1.5U eq (O) . Fig. 1

Special details
Experimental. 168 frames, detector distance = 120 mm 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 > 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.