The triazol-imidazol compound, 4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H-1,2,4-triazol-3(4H)-one (3), (C15H17N5O), was prepared and characterized by H-1 NMR, C-13 NMR, IR and single-crystal X-ray diffraction. By using the density functional theory (DFT) method with 6-31G(d) basis set, the molecular geometry, vibrational frequencies and gauge including atomic orbital (CIAO) H-1 and C-13 NMR chemical shift values of the title compound (3) in the ground state were calculated and compared with the experimental data. The calculated results are show that the optimized geometry can well reproduce the crystal structure. X-ray, FT-IR and NMR spectral results of the title compound (3) indicate that the compound exists as keto form. To determine most favorable conformation as theoretically, molecular energy profile of the title compound (3) were obtained as a function of the selected torsion angles T(N1-C8-C7-C6), T1 and T(C8-N1-C10-C11), T2, which is varied from -180 degrees to +180 degrees in every 10 by semi-empirical (PM3) calculations. In addition, DFT calculations of the title compound (3), molecular electrostatic potential and frontier molecular orbitals were performed at B3LYP/6-31G(d) level of theory. (C) 2010 Elsevier B.V. All rights reserved.