Anomalous Proton NMR Deshielding in Anilinopyrazoles

In connection with the synthesis of thienobenzodiazepines and certain heterocyclic analogues¹, a number of anilino heterocycle precursors were prepared. Their proton NMR spectra were generally unexceptional with the exclusion of one of the pyrazole isomers which showed a remarkable deshielding of one proton signal in the aniline ring. Further investigations have inferred that this low field shift can be attributed to through speace deshielding by a proximal pyrazole nitrogen lone pair.