GIAO/DFT studies on 1,2,4-triazole-5-thiones and their propargyl derivatives

Density functional theory (DFT)/Becke-Lee-Yang-Parr (B3LYP) and gauge-including atomic orbital (GIAO) calculations were performed on a number of 1,2,4-triazole derivatives, and the optimized structural parameters were employed to ascertain the nature of their predominant tautomers. (13)C and (15)N NMR chemical shifts of 3-substituted 1,2,4-triazole-5-thiones and their propargylated derivatives were calculated via GIAO/DFT approach at the B3LYP level of theory with geometry optimization using a 6-311++G** basis set. A good agreement between theoretical and experimental (13)C and (15)N NMR chemical shifts could be found for the systems investigated. The data generated were useful in predicting (15)N chemical shifts of all the nitrogen atoms of the triazole ring, some of which could not be obtained in solution state (15)N HMBC/HSQC NMR measurements. The energy profile computed for the dipropargylated derivatives was found to follow the product distribution profile of regioisomers formed during propargylation of 1,2,4-triazole thiones.