Ethyl 4-butylamino-3-nitrobenzoate

In the crystal structure of the title compound, C13H18N2O4, the asymmetric unit consists of three crystallographically independent ethyl 4-butylamino-3-nitrobenzoate molecules. There is an intramolecular N—H⋯O hydrogen bond in each molecule, which generates an S(6) ring motif. The structure is stabilized by intermolecular N—H⋯O and C—H⋯O hydrogen bonds.

In the crystal structure of the title compound, C 13 H 18 N 2 O 4 , the asymmetric unit consists of three crystallographically independent ethyl 4-butylamino-3-nitrobenzoate molecules. There is an intramolecular N-HÁ Á ÁO hydrogen bond in each molecule, which generates an S(6) ring motif. The structure is stabilized by intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds. H atoms treated by a mixture of independent and constrained refinement Á max = 0.31 e Å À3 Á min = À0.25 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).
In the crystal structure, in two molecules (A & B), the hydrogen atom attached to the nitrogen atom is hydrogen-bonded to the nitro group oxygen atoms via N-H···O hydrogen bonds to form tandem hydrogen bonds. Here both the hydrogen atoms act as bifurcated donor and the oxygen atom act as bifurcated acceptor. In addition, these neighboring molecules are linked by C-H···O hydrogen bonds along the [1 0 0] direction. Interestingly enough, the molecules C are not linked by any intermolecular interactions (Fig. 2).

Experimental
The title compound was synthesized by adding N,N-diisopropyl ethylamine (DIPEA) (0.20 ml, 1.12 mmol) dropwise to a stirred solution of ethyl 4-fluoro-3-nitrobenzoate (0.21 g, 1 mmol) in dry dichloromethane (10 ml). Butylamine (0.10 ml, 1 mmol) was added slowly with stirring, and then the mixture was stirred overnight at room temperature under N 2 . After completion of the reaction, the mixture was washed with 10% Na 2 CO 3 (10 ml). The aqueous layer was washed again with dichloromethane (3 × 10 ml). The organic fractions were pooled, dried over MgSO 4 and the solvent was evaporated in vacuo. Recrystallization with hot hexane afforded the title compound as yellow needle-like crystals.

Refinement
H atoms were positioned geometrically (C-H = 0.93-0.97 Å) and refined using a riding model with U iso (H) = 1.2U eq (C) and 1.5U eq (methyl C). A rotating-group model was used for the methyl groups. The nitrogen H atoms were located from the difference Fourier map [N-H = 0.82 (3)-0.89 (3) Å] and allowed to refine freely. Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atom numbering scheme. Dashed lines indicate hydrogen bonding.    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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
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