N-(3,4-Dichlorophenyl)-3-oxobutanamide

In the title compound. C10H9Cl2NO2, the acetamide residue is twisted out of the phenyl ring plane by 25.40 (9)°. An intramolecular C—H⋯O close contact is observed. The N atom of the butanamide unit forms an intermolecular N—H⋯O hydrogen bond with the symmetry-related carbonyl O atom, interlinking molecules into a C(4) chain along [100]. Additional C—H⋯O intermolecular interactions and Cl⋯Cl contacts [3.4364 (8) Å] contribute to the stability of the crystal packing.

In the title compound. C 10 H 9 Cl 2 NO 2 , the acetamide residue is twisted out of the phenyl ring plane by 25.40 (9) . An intramolecular C-HÁ Á ÁO close contact is observed. The N atom of the butanamide unit forms an intermolecular N-HÁ Á ÁO hydrogen bond with the symmetry-related carbonyl O atom, interlinking molecules into a C(4) chain along [100]. Additional C-HÁ Á ÁO intermolecular interactions and ClÁ Á ÁCl contacts [3.4364 (8) Å ] contribute to the stability of the crystal packing.
In (I), the C═O bond lengths are 1.2292 (18) Å and 1.207 (2) Å which confirms that the compound is in the keto form ( Fig. 1). The phenyl ring (C1-C6) is planar with a maximum deviation of 0.007 (1) Å for the C1 atom, from the least-squares plane of the ring. The short C-N distances of 1.407 (2) and 1.346 (2) Å and C1-N-C7 larger bond angle of 126.9 (13)°m ay be attributed to the involvement of the butanamide N atom in the intermolecular N-H···O interaction and a short intramolecular contact (1.95 Å) between O1 and H0A which is less than their van der Waals radii (2.72 Å). Similar short contacts are also observed in other related structures containing the acetamide residue (Sundar et al., 2005;Guo, 2004;Robin et al., 2002). Atoms N, C7, O1 and C8 forming the acetamide residue are coplanar with a maximum deviation of -0.005 (2) Å for the C7 atom. The acetamide residue is twisted considerably from the least-squares plane of phenyl ring having a dihedral angle of 25.40 (9)°. Atoms C8, C9, O2 and C10 from the O-acetyl group are also coplanar displaying a dihedral angle of 49.21 (10)° with the mean plane of the phenyl ring (C1-C6) and 73.78 (11)° with the least-squares plane of the acetamide residue.
Following a density functional theory calculation (Schmidt & Polik 2007) at the B3LYP 6-31-G(d) level (Becke, 1988(Becke, , 1993Lee et al. 1988;Hehre et al. 1986) with the GAUSSIAN03 program package (Frisch et al. 2004) the angle between the mean planes of the C8/C9/O2/C10 and N/C7/O1/C8 groups change from 73.7 (8)° to 33.0 (2)°. The angle between the least-squares plane of the benzene ring and the mean planes of the C8/C9/O2/C10 and N/C7O1/C8 groups change from 49.2 (1)° and 25.4 (1)° to 30.1 (5)° and 3.6 (5)°, respectively. This results in twisting the C8═O2 keto group to be in the The title compound was prepared by a method similar to that of Lliopoulos et al. (1986). A solution of 3,4-dichloroaniline (10 mmol) in benzene (30 ml) was added to a solution of ethyl acetoacetate (10 mmol) and the reaction mixture was refluxed for 2 h with stirring. The resulting precipitate was collected by filtration, washed several times with benzene and dried in vacuo (yield 86%). An ethanol solution of the title compound was allowed to evaporate slowly and colorless crystals of (I) were obtained after a week.

Refinement
All of the H atoms were placed in their calculated positions and then refined using the riding model with C-H = 0.95-0.99 Å, N-H = 0.88Å and with U iso (H) = 1.19-1.50U eq (C) and 1.18U eq (N). Fig. 1. The molecular structure of C 10 H 9 NO 2 Cl 2 , (I), showing the atom-numbering scheme and 50% probability displacement ellipsoids. 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 )
x y z U iso */U eq