(S)-1-Methoxycarbonyl-2-(4-nitrophenyl)ethanaminium chloride

The title compound, C10H13N2O4 +·Cl−, comprises a Cl− anion and a protonated aminium cation. The crystal packing is stabilized by cation–anion N—H⋯Cl hydrogen bonds and N—H⋯O hydrogen bonds, building an infinite two-dimensional network parallel to the (001) plane. The S absolute configuration at the chiral center was deduced from the synthetic pathway and confirmed by the X-ray analysis.

The title compound is built up from a Clanion and a protonated amino group cation (Fig. 1). The nitro group and the benzene ring are nearly planar, they are only twisted to each other by a torsion angles of C2-C1-N1-O1 (2.1 (7)° ) and C6-C1-N1-O2 (4.4 (7)° ), and the methyl 2-aminopropanoate substituent group is a zig-zag chain.
The S absolute configuration at C8 is deduced from the synthetic pathway and confirmed by the X-ray analyses.

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 nitration amino acid was esterified with H 2 SO 4 and CH 3 OH at 110 °C for 12 h, the crude product was obtained by evaporated the solution, and then recrystallized with distilled water by adding 1 ml HCl to yield colorless block-like crystals, suitable for X-ray analysis.

Refinement
All H atoms attached to C atoms and N atoms were fixed geometrically and treated as riding with C-H = 0.96 Å (methyl), 0.97 Å (methylene), 0.98 Å (methine), 0.93 Å (aromatic) and N-H = 0.89 Å with U iso (H) = 1.2U eq (C except methyl) or U iso (H) = 1.5U eq (N and methyl C). Fig. 1. A view of the title compound with the atomic numbering scheme. Displacement ellipsoids were drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii.

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 > 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.

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