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. Copyright © 2013 John Wiley & Sons, Ltd.