The synthesis of 3-alkyl-4-(5-methyl-2-furylmethyl-enamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (2) from the reactions of 3-alkyl-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (1) with 5-methyl-furan-2-carboxyaldehyde is described. The acetylation reactions of the compounds 2 giving compounds 3 were investigated. The newly synthesized compounds were characterized using IR, ¹H-NMR, ¹³C-NMR, UV and MS spectral data. Antioxidant activities of new compounds synthesized were also investigated, and they showed good antioxidant activities. In addition, to investigate the effects of solvents and molecular structure upon acidity, compounds 2 were titrated potentiometrically with tetrabutylammonium hydroxide in four non-aqueous solvents (isopropyl alcohol, tert-butyl alcohol, DMF and acetonitrile). The half-neutralization potential values and the corresponding pK_a values were determined for all cases. Furthermore, isotropic ¹H and ¹³C nuclear magnetic shielding constants of compounds 2 and 3 were obtained by the gauge-including-atomic-orbital (GIAO) method at the B3LYP density functional level. The geometry of each compound has been optimized using the 6-311G basis set. Theoretical values were compared to the experimental data.