3-(p-Anisyl)sydnone

In the title sydnone compound [systematic name: 3-(4-methoxyphenyl)-1,2,3-oxadiazol-3-ium-5-olate], C9H8N2O3, the essentially planar oxadiazole ring [maximum deviation = 0.005 (1) Å] is inclined at a dihedral angle of 30.32 (8)° with respect to the benzene ring. In the crystal, adjacent molecules are interconnected by intermolecular C—H⋯O hydrogen bonds into sheets lying parallel to (100). Weak intermolecular π–π interactions [centroid–centroid distance = 3.5812 (8) Å] further stabilize the crystal packing.


Comment
Sydnones constitute a well-defined class of mesoionic compounds consisting of 1,2,3-oxadiazole ring system. The study of sydnones still remains a field of interest because of their electronic structure and also because of the varied types of biological activity displayed by some of them (Rai et al., 2008). Sydnone derivatives were found to exhibit promising anti-microbial properties (Hegde et al., 2008). Sydnones are synthesized by the cyclodehydration of N-nitroso-N-substituted amino acids using acetic anhydride. The sydnones unsubstituted in the 4-position readily undergo typical electrophilic substitution reaction namely formylation (Kalluraya & Rahiman, 1997) and acetylation (Kalluraya et al., 2002).
Experimental N-Nitroso-p-methoxyanilinoacetic acid (0.01 mol) was heated with acetic acid anhydride (0.5 mol) on a water bath for 2-3 h. The reaction mixture was kept aside at room temperature for overnight. It was then poured into ice-cold water. The obtained solid was dried and crystallized from benzene. Single crystals suitable for X-ray analysis were obtained from ethanol by slow evaporation.

Refinement
All H atoms were located from difference Fourier map and allowed to refine freely with range of C-H = 0.95 (2) -1.00 (2) Å. In the absence of significant anomalous dispersion, 1266 Friedel pairs were merged in the final refinement.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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.