Synthesis and GIAO NMR calculations for some novel 4-heteroarylidenamino-4,5-dihydro-1H-1,2,4-triazol-5-one derivatives:: Comparison of theoretical and experimental 1H- and 13C-chemical shifts

3-Alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (1) reacted with 5-methylfuran- 2-carboxyaldehyde to afford the corresponding 3-alkyl(aryl)-4-(5-methyl-2-furylmethylenamino)- 4,5-dihydro-1H-1,2,4-triazol-5-ones (2). Four newly synthesized compounds have been characterized by elemental analyses, IR, H-1-NMR, C-13-NMR and UV spectral data. In addition, isotropic H-1- and C-13-nuclear magnetic shielding constants of compounds 3 were calculated by employing the direct implementation of the gauge-including-atomic-orbital (GIAO) method at the B3LYP density functional and HF levels of the theory. The geometry of each compound has been optimized using a 6-311G basis set. Nuclear shielding constants were also calculated by using 6-311G basis set. Theoretical values are compared to the experimental data.