Carbon-13 nuclear magnetic resonance spectra of organic sulfur compounds. Comparison of chemical shifts for carbonyl and thiocarbonyl compounds in the pyrone, thiopyrone, and pyridone series

13C nmr data have been obtained for a series of 2- and 4-pyrones and pyridones, and their sulfur-containing analogues. Correlations have been observed between the nature of the ring hetero-atom and the chemical shift difference (Δδ) for the Cα and Cβ carbons in these conjugated systems. No significant correlation, however, appears to exist between the chemical shifts of the C=O and C=S groups. Substituent chemical shift (s.c.s.) effects for various simple substituents are compared with those in related series of compounds.