2-(3,4-Dichlorophenyl)-N-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)acetamide

In the title compound, C19H17Cl2N3O2, there are three molecules (A, B and C) in the asymmetric unit and each differs in the conformation adopted. As a result of steric repulsion, the amide group is rotated with respect to both the dichlorophenyl and 2,3-dihydro-1H-pyrazol-4-yl rings, making dihedral angles of 44.5 (2) and 56.2 (2)°, respectively in A, 51.1 (2) and 54.1 (2)° in B, and 53.8 (2) and 54.6 (2)° in C. The dihedral angles between the dichlorophenyl and 2,3-dihydro-1H-pyrazol-4-yl rings are 54.8 (2), 76.2 (2) and 77.5 (2)° in molecules A, B and C, respectively, while the 2,3-dihydro-1H-pyrazol-4-yl and phenyl rings make dihedral angles of 45.3 (2), 51.2 (2) and 42.8 (2)°, respectively. In the crystal, two of the molecules are linked through N—H⋯O hydrogen bonding to an adjoining molecule, forming dimers of the R 2 2(10) type, while the third molecule forms such dimers with itself. C—H⋯O interactions link the dimers.

In the title compound, C 19 H 17 Cl 2 N 3 O 2 , there are three molecules in the asymmetric unit and each differs in the comformation adopted. In each molecule the amide group is planar but two of the molecules (B and C) are linked through N-H···O hydrogen bonding to an adjoining molecule forming dimers of the R 2 2 (10) type (Bernstein et al., 1995) while molecule A forms such dimers with itself. The major conformational difference between three molecules is seen in the dihedral angles between the dichlorophenyl and 2,3-dihydro-1H-pyrazol-4-yl rings which are 54.8 (2)°, 76.2 (2),° and 77.5 (2)° for A, B, and C, respectively. Due to steric repulsion the amide group is rotated with respect to both the dichlorophenyl and 2,3-dihydro-1H-pyrazol-4-yl rings with dihedral angles of 44.5 (2)° and 56.2 (2)° for A; 51.1 (2) and 54.1 (2) for B; and 53.8 (2) and 54.6 (2) for C. All other metrical parameters are in the normal ranges (Allen, 2002).

Experimental
3,4-Dichlorophenylacetic acid (0.240 g, 1 mmol) and 4-aminoantipyrine (0.203 g, 1 mmol), 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (1.0 g, 0.01 mol) and were dissolved in dichloromethane (20 ml). The mixture was stirred in presence of triethylamine at 273 K for about 3 h. The contents were poured into 100 ml of ice-cold aqueous hydrochloric acid with stirring, which was extracted thrice with dichloromethane. The organic layer was washed with saturated NaHCO 3 solution and brine solution, dried and concentrated under reduced pressure to give the title compound (I). Single crystals were grown from methylene chloride by the slow evaporation method (m.p.: 473-475 K).

Refinement
The H atoms were placed in calculated positions and refined in the riding mode: N-H = 0.

Figure 1
The molecular structure of the title molecule with the atom numbering. The displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The crystal packing of the title compound, viewed along the b axis. Hydrogen bonds are shown as dashed lines -see   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.