1,2,3-Oxadiazole is a five-membered, unsaturated, unstable, nonbenzenoid, heteroaromatic, comprised of two carbon atoms, one oxygen atom, and two pyridine-type nitrogen atoms linked in continuity (O-N-N). Depending on the position of the nitrogen atoms, the four possible regioisomeric structures are generated for oxadiazoles. The cyclic structure for 1,2,3-oxadiazoles is unstable and readily isomerizes to α-diazoketone, an open chain structure.
3-Phenylsydnone is a crystalline compound prone to hydrolysis with ring cleavage, especially in basic medium. The carbonyl stretching frequency in the IR spectra of sydnones is found in the range of 1720–1790 cm–1 depending on the substituent present. The UV spectra of alkylsydnones showed a single maxima at 290 nm.
