HOMO–LUMO, UV, NLO, NMR and vibrational analysis of 3-methyl-1-phenylpyrazole using FT-IR, FT-RAMAN FT-NMR spectra and HF-DFT computational methods

• The compound 3-methyl-1-phenylpyrazole has been investigated using FT-IR, FT-Raman and NMR and UV–Vis spectroscopic tool.
• The vibrational properties of the molecule have been studied.
• The stable geometry of the molecule through conformational study is carried out.
• The charge transfer in the molecule by HOMO–LUMO studied.
• A strong correlation has been revealed between the Mullikan atomic charges and the NMR chemical shifts.

In this paper, the spectral analysis of 3-methyl-1-phenylpyrazole is carried out using the FT-IR, FT Raman, FT NMR and UV–Vis spectra with the help of quantum mechanical computations using HF and density functional theories. The different conformers of the compound and their minimum energies are studied using B3LYP functional with 6-311+G (d, p) basis set and the most stable conformer with minimum energy was identified and the same conformer was used for further computations. The computed wave numbers from different methods are scaled so as to agree with the experimental values and the scaling factors are reported. All the modes of vibrations are assigned and the structure the molecule is analyzed in terms of parameters like bond length, bond angle and dihedral angle predicted by both HF and B3LYP methods with 6-311+G (d, p) and 6-311++G (d, p) basis sets. The values of dipole moment (μ), polarizability (α) and hyperpolarizability (β) of the molecule are reported, using which the non-linear property of the molecule is discussed. The HOMO–LUMO mappings are reported which reveals the different charge transfer possibilities within the molecule. The isotropic chemical shifts predicted for 1H and 13C atoms using gauge invariant atomic orbital (GIAO) theory show good agreement with experimental shifts. NBO analysis is carried out to picture the charge transfer between the localized bonds and lone pairs. The thermodynamic properties (heat capacity, entropy and enthalpy) at different temperatures are also calculated.

The 3-methyl-1-phenylpyrazole has got versatile pharmaceutical application as anti-cancer, anti-fungal, anti-viral, anti-oxidant. It is also used as insecticide. The investigation of the molecule presents the stable structure with lowest energy. The reactivity descriptors indicate the electrophilic and electro phobic nature of molecule. The observed chemical shifts of carbon and hydrogen indicate the activity of the molecule in the magnetic field. The contour map shows electron density flow in the molecule.Figure optionsDownload as PowerPoint slide