1-Phenyl-1H-pyrazole-4-carbaldehyde

In the title molecule, C10H8N2O, the five- and six-membered rings form a dihedral angle of 10.14 (9)°. The aldehyde group is almost coplanar with the pyrazole ring to which it is connected [O—C—C—C torsion angle = −179.35 (17)°]. In the crystal, inversion dimers are linked by four C—H⋯O interactions as the carbonyl O atom accepts two such bonds. The dimeric aggregates are linked into supramolecular layers in the ac plane by C—H⋯π and π–π [ring centroid(pyrrole)⋯ring centroid(phenyl) = 3.8058 (10) Å] interactions.

In the title molecule, C 10 H 8 N 2 O, the five-and six-membered rings form a dihedral angle of 10.14 (9) . The aldehyde group is almost coplanar with the pyrazole ring to which it is connected [O-C-C-C torsion angle = À179. 35 (17) ]. In the crystal, inversion dimers are linked by four C-HÁ Á ÁO interactions as the carbonyl O atom accepts two such bonds. The dimeric aggregates are linked into supramolecular layers in the ac plane by C-HÁ Á Á and -[ring centroid(pyrrole)Á Á Áring centroid(phenyl) = 3.8058 (10) Å ] interactions.
In (I), Fig. 1, the dihedral angle between the five-and six-membered rings is 10.14 (9) °, indicating a slight twist in the molecule. The aldehyde group is co-planar with the pyrazole ring to which it is connected as seen in the value of the O1 -C1-C2-C3 torsion angle of -179.35 (17)°.

Experimental
N,N-Dimethylformamide (25.6 ml, 0.33 mmol) was stirred in around flask within an ice-bath and POCl 3 (21.6 ml, 0.23 mmol) was added drop-wise. Then N-phenylpyrazole was added (4.4 ml, 0.033 mmol) to this cold mixture. The reaction was allowed to warm to room temperature and then heated at reflux for 6 h. The temperature was kept at 368-373 K.
When the reaction was completed, the contents were poured onto crushed ice and made weakly alkaline with a saturated solution of sodium carbonate. The solid was filtered off, washed with water and recrystallized from ethanol. Yield: 65%.

Refinement
H-atoms were freely refined; the range of C-H bond lengths is 0.960 (17)-1.023 (18) Å. Owing to poor agreement, the (3 2 6) reflection was omitted from the final cycles of refinement.