NMR study of some sydnones,isosydnones, and isothiosydnones

Multinuclear¹H,¹³C,¹⁴N,¹⁵N, and¹⁷O NMR data are presented for some sydnones, isosydnones and isothiosydnones. The type of valence tautomerism shown in (Fig. 1) is not observed for the compounds studied. At high pH compounds2 and12 are found to undergo transformations. The more suitable NMR parameters are reported for establishing the structures of mesoionic compounds containing three heteroatoms in the five-membered conjugated ring. Someab initio GIAO calculations on a model structure of sydnones and related compounds have been performed.