In the present study novel 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5(4H)-one (compound (4)) and 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-5(4H)-thione (compound (5)) were synthesized. These oxadiazole ring derivatives were characterized by IR, H-1 NMR, C-13 NMR and HRMS analyses. The solvent effects on C=O, C=N and C=S stretching vibrational frequencies (v(C=O), v(C=N) and v(C=S)) of synthesized compounds were investigated experimentally using attenuated total reflection (ATR) infrared spectroscopy and compared with the theoretical results assigned using the potential energy distribution (PED) contributions. Furthermore, the v(C=O), v(C=N) and v(C=S) of compound (4) and compound (5) were correlated with empirical solvent parameters such as the solvent acceptor numbers, the Swain equation, the Kirkwood-Bauer-Magat equation, and the linear solvation energy relationships. Apart from the linear effects investigated in similar studies, solvent-induced vibrational shifts were investigated using the quadratic equation. The prediction capabilities of empirical solvent parameters were statistically compared. It was found that the linear solvation energy relationships show better correlation than the other empirical solvent parameters. Additionally, the quadratic equation provided more accurate predictions for the vibrational frequency locations than the Swain and the linear solvation energy relationships equations. (c) 2020 Elsevier B.V. All rights reserved.