Azapentalenes. XLIV. ¹H and ¹³C-NMR study of mesoionic pyrazolo[1,2-a]pyrazoles

Abstract

The ¹H and ¹³C chemical shifts as well as the ¹H–¹H and ¹H–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.