(S)-2-Ammonio-3-(4-nitrophenyl)propanoate monohydrate

The title compound, C9H10N2O4·H2O, exists as a zwitterion with a deprotonated carboxyl group and a protonated amino group. The crystal packing is stabilized by N—H⋯O and O—H⋯O hydrogen bonds, building sheets parallel to the (001) plane. The absolute configuration was deduced from the synthetic pathway.

The title compound, C 9 H 10 N 2 O 4 ÁH 2 O, exists as a zwitterion with a deprotonated carboxyl group and a protonated amino group. The crystal packing is stabilized by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, building sheets parallel to the (001) plane. The absolute configuration was deduced from the synthetic pathway.
The title compound exists as a zwitter ion with a deprotonated carboxyl group and a protonated amino group (Fig. 1). It crystallizes with one water molecule in the asymmetric unit. The crystal packing is stabilized by N-H···O and O-H···O hydrogen bonds building sheets parallel to the (0 0 1) plane ( The S absolute configuration at C8 is deduced from the synthetic pathway.

Experimental
Under nitrogen protection, 2-amino-3-phenylpropanoic acid (30 mmol), nitric acid (50 mmol) and sulfuric acid (20 mmol) were added in a flask. The mixture was stirred at 110 °C for 3 h. The resulting solution was poured into ice water (100 mL), then filtered and washed with distilled water. The crude product was recrystallized with distilled water to yield colorless block-like crystals, suitable for X-ray analysis.

Refinement
All H atoms attached to C atoms and N atom were fixed geometrically and treated as riding with C-H = 0.98 Å (methine), 0.97 Å (methylene), 0.93 Å (aromatic) and N-H = 0.89 Å with U iso (H) = 1.2U eq (C) or U iso (H) = 1.5U eq (N). H atoms of water molecule were located in difference Fourier maps and included in the subsequent refinement using restraints (O-H= 0.85 (1)Å and H···H= 1.39 (2)Å) with U iso (H) = 1.5U eq (O). In the last stage of refinement they were treated as riding on their parent O atom.
In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined by the X-ray analyses and then the Friedel pairs were merged and any references to the Flack parameter were removed.

Special details
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.