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

Abstract

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.

Synthesis, Characterisation, Theoretical NMR Calculations and Crystal Structure of the 3-methyl-1H-1,2,4?4-triazole-5-amine acetate

“…As shown in Table 7S, the chemical shift calculation for the NH hydrogen of the mta-A' was at δ 2.5949 by the B3LYP/6-311+G(d,p) and at δ 2.5227 by the PBE1PBE/6-311++G(d,p) levels of theory. These shifts are lower compared to those reported in the literature (δ 6.3-5.8), suggesting that this hydrogen atom is active by hydrogen bonding or tautomerism Phalgune et al, 2013). The percentage error in the calculated chemical shift of the carbon atom from the group C(NH2), compared with the reported experimental data, was 0.41% and 1.14% by the levels of theory B3LYP/6-311+G(d,p) and PBE1PBE/6-311++G(d,p).…”

“…The experimental and calculated NMR data for the mpta compound are shown in Tables 4S and 5S (see Supplementary Material). The calculated hydrogen NMR data for the NH group revealed an active hydrogen atom due to the lower calculated chemical shift in comparison with the experimental data Phalgune et al, 2013). In general, the computational data with good correlation (0.9934 -0.9982) were similar to the calculations in gaseous phase (MP4) and DFT, considering solvation by DMSO through the implicit model.…”

“…The less percentage error for the isomer C by both level of theory suggest this isomer is the most probable in solution as shown by Figure 7. Yet again, the calculated chemical shift for the hydrogen of the NH group is also below that of the experimental data, suggesting an active hydrogen atom by hydrogen bonding or tautomerism Phalgune et al, 2013).…”

“…The optimized geometries by MP4 (sdq)/6-31G(d,p), and DFT/B3LYP/6-311++G(2d,2p) were used in carbon chemical shift calculations. The levels of theory B3LYP/6-31G(d,p), B3LYP/6-311+G(d,p), and PBE1PBE/6-311++G(d,p) were applied considering solvation by the DMSO Phalgune et al, 2013;Ünlüer et al, 2019). The calculated carbon chemical shifts (σC) were obtained relative to the corresponding calculated values for tetramethylsilane at the same levels of theory.…”

Synthesis and Cytotoxicity of Some Imidazo[4,5‐b]pyridine Derivatives and Their Regioselective N‐Alkylation

“…In particular, 1 H‐ 15 N heteronuclear multiple‐bond correlation (HMBC) experiment has been frequently used for measurements of 15 N chemical shifts and 1 H− 15 N coupling constants differentiation of mixture of some regioisomers (Figure 5). [14–19] …”