Nitrogen NMR spectroscopy: Application to some substituted pyrroles

A series of 15 N labeled 2‐acylpyrroles was prepared and the nitrogen and proton n.m.r. spectra obtained. 15 N chemical shifts for these compounds are reported for the first time. No correlation between the nitrogen chemical shift and any Hammett substituent constant could be found. No variation in J ( 15 NH) was observed for any compound with changes in solvent, temperature or concentration, ruling out any observable tautomeric equilibria for these systems. An increase in J ( 15 NH) with the addition of electron withdrawing groups indicates increasing polarization of the NH bond and acidity of these molecules. Two and three bond 15 N couplings are also reported.