Structural studies of intramolecularly hydrogen-bonded vinylogous thiocarboxamides. NMR and isotope experiments and a DFT theoretical study

This study examines the structural properties of intramolecularly hydrogen-bonded vinylogous thiocarboxamides through NMR spectroscopy, isotope effects on chemical shifts, atoms-in-molecules (AIM), and density functional theory (DFT) calculations. The functionals ωB97XD, M062X, CAM-B3LYP, and B3LYP using the (6–311++G) (d,p) basis set were used for the DFT calculations. This study characterized three tautomers of vinylogous thiocarboxamide derivatives, with the enaminothione tautomer having the highest stability. The AIM analysis demonstrated that the hydrogen bonds in these systems exhibit moderate strength. This study also revealed correlations between the strengths of hydrogen bonds and different geometric parameters, providing a novel understanding of the physicochemical features of these systems. The combination of computational models and experimental data yields a thorough comprehension of the intramolecular hydrogen bonding in vinylogous thiocarboxamide derivatives, hence offering insights for future chemical synthesis and functionalization approaches.