The title molecule (C19H17N5O4S center dot H2O) was synthesized and characterized by IR-NMR spectroscopy. MS and single-crystal X-ray diffraction. The molecular geometry, vibrational frequencies and gaugeindependent atomic orbital (GIAO) H-1 and C-13 NMR chemical shift values of the compound in the ground state have been calculated by using the density functional theory (DM method with 6-31G(d) basis set, and compared with the experimental data. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and H-1 and C-13 NMR chemical shift values show good agreement with experimental data. To determine conformational flexibility, the molecular energy profile of the title compound was obtained with respect to the selected torsion angle, which was varied from -180 degrees to +180 degrees in steps of 10 degrees. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and thermodynamic properties of the compound were investigated by theoretical calculations. (C) 2011 Elsevier B.V. All rights reserved.