A ^(15)N NMR investigation of some azolopyridines

Abstract

^(15)N NMR chemical shift data are presented for 14 azolopyridines, together with the results of INDO/S-SOS calculations of nitrogen shieldings. Previous ^(14)N NMR results for some of these compounds are reinterpreted. The ^(14)N data and their assignments are shown to be reliable for the indolizine nitrogen atom from arguments based on relative line widths. The pyridine-type nitrogens are more reliably assigned from the ^(15)N spectra combined with the results of the INDO/S-SOS calculations for individual molecules. A combination of ^(14)N and ^(15)N NMR spectra, together with the shielding calculations, provides a basis for unambiguous assignments of all the various nitrogen environments considered.