Azapentalenes. XLIV.1H and13C-NMR study of mesoionic pyrazolo[1,2-a]pyrazoles

Abstract

The1H and13C chemical shifts as well as the1H–1H and1H–13C coupling constants of sixteen pyrazolo[1,2-a]pyrazole derivatives have been measured. The most relevant features are discussed using resonance forms and simple additive models. AM1 semi-empirical calculations have been carried out to provide a rationale for the NMR results.