2-[4-(2-Chlorobenzyl)-3-methyl-6-oxo-1,6-dihydropyridazin-1-yl]-N-(4-fluorophenyl)acetamide

An intramolecular C—H⋯O hydrogen bond helps to determine the conformation of the title molecule in which the 2-chlorobenzyl group is rotationally disordered.


Synthesis and crystallization
A mixture of 3-benzylidene-4-oxopentanoic acid derivative (0.010 mol) and hydrazine hydrate (0.020 mol) in ethanol was refluxed to obtain the 5-(2-chlorobenzyl)-6-methylpyridazin-3(2H)-one precursor.To this pyridazine-3(2H)-one (0.010 mol) was added 0.010 mol of 2-chloro-N-(4-fluorophenyl)acetamide, followed by 0.020 mol of potassium bicarbonate and a spatula tip of BTBA (benzyltributylammonium bromide).The mixture was kept stirring at room temperature for 24 h and the progress of the reaction was monitored by TLC.Then, 200 ml of distilled water were added to the reaction mixture, the precipitated product was filtered off, dried and recrystallized from acetone solution to yield colorless crystals of the title compound.

Figure 1
The title molecule with labeling scheme and 50% probability ellipsoids.
The intramolecular C-H� � �O hydrogen bond is depicted by a dashed line and only the major component of the disorder is shown.

Special details
Experimental.The diffraction data were collected in three sets of 363 frames (0.5° width in ω) at φ = 0, 120 and 240°.A scan time of 40 sec/frame was used.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.H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.99 Å) and were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms.That attached to nitrogen was located in a difference map and refined with a DFIX 0.91 0.01 instruction.The o-chlorobenzyl group is rotationally disoordered over two sites 177.2 (5)° apart in a 0.656 (2)/0.344(2) ratio.The two components were refined as rigid hexagons with additional restraints to make their geometries comparable.One reflection affected by the beam stop was omitted from the final refinement.

Figure 2 A
Figure 2A portion of one chain of molecules viewed along the a-axis direction with N-H� � �O hydrogen bonds and slipped, �-stacking interactions depicted, respectively, by violet and orange dashed lines.Non-interacting hydrogen atoms are omitted for clarity.

Figure 3
Figure 3 Packing viewed along the a-axis direction with N-H� � �O, C-H� � �O and C-H� � �F hydrogen bonds depicted, respectively, by violet, black and light blue dashed lines.Slipped �-stacking interactions are depicted by orange dashed lines and non-interacting hydrogen atoms are omitted for clarity.

Table 2
Experimental details.