Crystal structure of 2-methyl-4-[(thiophen-2-yl)methylidene]-1,3-oxazol-5(4H)-one

The asymmetric unit of the title compound, C9H7NO2S, contains two crystallographically independent molecules (A and B). Both molecules are almost planar [maximum deviations = 0.047 (1) and 0.090 (1) Å, respectively, for the S atoms] with the oxazole and thiophene rings being inclined to one another by 2.65 (16)° in molecule A and by 4.55 (15)° in molecule B. In the crystal, the individual molecules are linked via C—H⋯O hydrogen bonds, forming –A–B–A–B– chains along the [10-1] direction. The chains are linked via C—H⋯π and π–π interactions [intercentroid distances = 3.767 (2) and 3.867 (2) Å] involving inversion-related oxazole and thiophene rings in both molecules, forming a three-dimensional structure.


S2. Experimental
A mixture of acetyl glycine (2 g, 0.017 mol), thiophene-2-carbaldehyde (1.91 g, 0.017 mol), anhydrous sodium acetate (1.39 g, 0.017 mol) and acetic anhydride (5.20 g, 0.051 mol) was heated on electric plate with constant stirring. As soon as the mixture liquefied completely, the resulting solution was refluxed for 2 h. 25 ml of ethanol was added slowly to the contents of the flask and the mixture was allowed to stand overnight in a refrigerator. The solid mass that separated out was stirred with 60 ml of cold water, filtered, washed with cold water and recrystallized from carbon tetrachloride. Single crystals were grown from chloroform by the slow evaporation method (m.p.: 411-412 K).

S3. Refinement
All the H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.96 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.

Figure 1
A view of the molecular structure of the two independent molecules of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 40% probability level.

Figure 2
A view along the b axis of the crystal packing of the title compound. The C-H···O ydrogen bonds are shown as dashed lines (see Table 1 for details; molecule A blue; molecule B red).

2-Methyl-4-[(thiophen-2-yl)methylidene]-1,3-oxazol-5(4H)-one
Crystal data C 9 H 7 NO 2 S M r = 193.22 Monoclinic, P2 1 /n Hall symbol: -P 2yn a = 12.2264 (11) Å b = 9.8581 (7)  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.