Synthesis, spectroscopic characterization and quantum chemical computational studies on 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole

The pyrazole compound 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole, (C19H18N2O), was characterized by X-ray single crystal diffraction technique, IR–NMR spectroscopy and quantum chemical computational methods as both experimental and theoretically. The compound crystallizes in the monoclinic space group C 2/c with a = 32.5334 (1) Å, b = 5.8060 (1) Å, c = 23.6519 (8) Å, β = 134.572 (2)°, and Z = 8. The molecular geometry was also optimized using the Hartree–Fock (HF) and density functional theory (DFT/B3LYP) methods with the 6-311G(d,p) basis set and compared with the experimental data. To determine conformational flexibility, molecular energy profile of the tittle compound was obtained by semi-empirical (AM1) with respect to selected degree of torsional freedom, which was varied from −180° to +180° in steps 10°. From the optimized geometry of the molecule, vibrational frequencies, gauge-independent atomic orbital (GIAO) 1H and 13C NMR chemical shift values, molecular electrostatic potential (MEP) distribution, non-linear optical properties, frontier molecular orbitals (FMOs) of the title compound have been calculated in the ground state theoretically. The theoretical result showed good agreement with the experimental values.

► Pyrazole, X-ray single crystal diffraction.
► Density functional theory (DFT) and Hartree–Fock (HF).
► Molecular electrostatic potential (MEP) distribution and non-linear optical properties (NLO).