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 K. Carthigayan a,b,⇑ , S. Xavier b,c , S. Periandy d a Department of Physics, Women’s Polytechnic College, Puducherry, India b Bharathiyar University, Coimbatore, Tamil Nadu, India c Department of Physics, St. Joseph College of Arts and Science, Cuddalore, Tamil Nadu, India d Department of Physics, Tagore Arts College, Puducherry, India highlights  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. graphical abstract 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 nat- ure of molecule. The observed chemical shifts of carbon and hydrogen indicate the activity of the mole- cule in the magnetic field. The contour map shows electron density flow in the molecule. article info Article history: Received 7 November 2014 Received in revised form 3 February 2015 Accepted 6 February 2015 Available online 14 February 2015 Keywords: 3-Methyl-1-phenylpyrazole Chemical shifts NBO HOMO–LUMO abstract 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 ener- gy was identified and the same conformer was used for further computations. The computed wave num- bers 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 (l), polarizability (a) and hyperpolarizability (b) 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 pos- sibilities within the molecule. The isotropic chemical shifts predicted for 1 H and 13 C atoms using gauge invariant atomic orbital (GIAO) theory show good agreement with experimental shifts. NBO analysis is http://dx.doi.org/10.1016/j.saa.2015.02.035 1386-1425/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel./fax: +91 9442033731. E-mail address: carthirohit@gmail.com (K. Carthigayan). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 350–363 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa