Nuclear magnetic resonance studies of heteroaromatic systems. Methyl coupling of 2‐substituted picolines, 2‐pyridones and 2‐pyridthiones

The proton magnetic resonance spectra of all the 2‐amino‐, 2‐chloro‐, 2‐nitropicolines were determined. Long‐range coupling of the methyl groups to all available ortho (four bonds) and para (six bonds) ring protons was found in these picolines. The p.m.r. spectra of all of the ring methyl substituted 2‐pyridones and 2‐pyridthiones were analyzed. In 4‐ and 5‐methyl‐2‐pyridones and the corresponding thiones, selective ring coupling was observed to only one ortho ring proton, viz. , to H‐3 and H‐6 respectively. However, in 3‐ and 6‐methyl‐2‐pyridones and analogous thiones, long‐range coupling was visible to both ortho and para ring protons. These long‐range spin‐spin interactions are interpreted in terms of the structures of 2‐pyridones and their thione analogs.