3-(2-Acetamidophenyl)sydnone

Sydnones are unusual mesoionic compounds containing a five-membered heterocyclic ring. Generally for stability, substitution at the N-3 position by an aromatic fragment is necessary. In the title compound, C10H9N3O3, the aromatic substitutent is 2-acetamidophenyl. The two planar ring fragments are twisted relative to one another, with a interplanar angle of 63.13 (5)°. The molecules are packed into the unit cell via π–π interactions between the phenyl rings [interplanar separation = 3.4182 (4) Å] and between the sydnone rings [interplanar separation = 3.2095 (4) Å]. N—H⋯O and C—H⋯O hydrogen bonding is also found internally and externally to the molecule.

Sydnones are unusual mesoionic compounds containing a fivemembered heterocyclic ring. Generally for stability, substitution at the N-3 position by an aromatic fragment is necessary. In the title compound, C 10 H 9 N 3 O 3 , the aromatic substitutent is 2-acetamidophenyl. The two planar ring fragments are twisted relative to one another, with a interplanar angle of 63.13 (5) . The molecules are packed into the unit cell viainteractions between the phenyl rings [interplanar separation = 3.4182 (4) Å ] and between the sydnone rings [interplanar separation = 3.2095 (4) Å ]. N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonding is also found internally and externally to the molecule.

Comment
Sydnones are the most widely studied members of the general class of mesoionic compounds (Ohta & Kato, 1969). They are the products of dehydration of N-nitroso-α-aminoacids (Hope & Thiessen, 1968), and they undergo facile electrophilic aromatic subtitution on the sydnone ring. The selectivity on the sydnone ring (and not the aryl ring) can be attributed to the activated nature of the sydnone ring (Matsunaga, 1957) and its deactivating effect upon the attached aryl ring (the N3 position bears a considerable fractional positive charge (Kier & Roche, 1966)).
The 3-(2-acetamidophenyl)sydnone was synthesized to investigate its bromination and to probe the parameters controlling the site of electrophilic attack, both from mechanistic and synthetic standpoints. The sydnone ring is found to be planar. The ring bond distances O-N, N-N, N-C and C-C are similar to those of related compounds. However, the C-O bond distance of 1.4158 (12)Å, is longer than that of the C-O bond in a furane ring. As mentioned in previous paper (Hodson & Turnbull, 1985), the exocyclic C═O distance (1.2181 (12)Å) does not support the formulation of Baker & Ollis (1957), which involves the delocalization of a positive charge on the ring, and a negative charge on the exocyclic oxygen.
The molecules pack along the body diagonal within the unit cell, in symmetry related pairs with the phenyl rings lying parallel to each other, separated by a distance of 3.4182 (4)Å. The pairs of molecules are further paired through interaction of the sydnone rings in adjacent molecules, which are positioned parallel to each other at a distance of 3.2095 (4)Å. The molecules are connected laterally through hydrogen bonding between the sydnone and acetamide O atoms and phenyl, and amide H atoms. Hydrogen bond parameters are tabulated in Table 1.

Refinement
The amide H atom was located in a different Fourier map and refined with an isotropic displacement parameter. The positional parameters were allow to refine freely. The methyl and benzene H atoms were included in geometrically calculated positions, with C-H distances of 0.98Å and 0.96Å, respectively, and U iso (H) = 1.3U eq (C).  Fig. 1. Molecular structure of title compound with the atom numbering scheme. The displacement ellipsoids are drawn at 50% probability level. The H atoms are presented as a small spheres of arbitrary radius.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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.