Molecular structure and vibrational and chemical shift assignments of 6-(2-hydroxyethyl)-2,3,4-triphenyl-2,6-dihydro-7H-pyrazolo[3,4-d]pyridazin-7-one by DFT and ab initio HF calculations

The molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO) 1H and 13C chemical shift values and several thermodynamic parameters of 6-(2-hydroxyethyl)-2,3,4-triphenyl-2,6-dihydro-7H-pyrazolo[3,4-d]pyridazin-7-one in the ground state have been calculated by using the Hartree-Fock (HF) and density functional methods (B3LYP) with 6-31G(d) basis set. The results of the optimised molecular structure are presented and compared with the experimental X-ray diffraction. The calculated results show that the optimised geometries can well reproduce the crystal structural parameters and the theoretical vibrational frequencies, and 1H and 13C NMR chemical shift values show good agreement with experimental data. The computed vibrational frequencies are used to determine the types of molecular motions associated with each of the experimental bands observed. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) with respect to selected degree of torsional freedom, which were varied from −180° to +180° in steps of 10°. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO), and thermodynamic properties were performed at HF and DFT levels of theory.