Experimental and computational spectroscopic studies of 3,5-disubstituted 4,5-dihydro-1,2,4-oxadiazoles

Some 3,5-disubstituted 4,5-dihydro-1,2,4-oxadiazoles (DHOZs) were synthesized, and steric and electronic effects of the substituents on the heterocyclic ring C3- and C5-positions were investigated using the NMR and UV-Vis spectroscopies, and (TD)DFT/6-311++G(d,p) computations. The NMR and UV-Vis spectroscopic characteristics of the synthesized compounds could be explained in terms of the pi- and sigma- electronic effects of the C3- and C5-aryl substitutions on the heterocyclic ring, respectively. Computational NMR chemical shifts and spin-spin coupling constants of the C5-H and N4-H protons display a Karplus correlation with corresponding H-C5-N4-H dihedral angle. The experimental and computational H-1 NMR chemical shifts of the C5-H proton show very good compatibility. Conformational analysis on the o-nitro and o-methoxyphenyl C5-substituted DHOZs showed intramolecular interactions affecting their structural and spectroscopic features. (C) 2020 Elsevier B.V. All rights reserved.