Computation and interpretation of vibrational spectra on the structure of Losartan using ab initio and Density Functional methods

• FT-IR, FT-Raman and UV–Vis spectra of Losartan in the solid phase were recorded and analyzed.
• Selected vibrational assignment and spectroscopic analysis have been carried out.
• Natural atomic analysis explained the intramolecular hydrogen bonding.
• The calculated HOMO and LUMO energies show that charge transfers occurs within molecule.
• The 13C and 1H NMR chemical shift data assignment for Losartan have also been reported.

The solid phase FTIR and FT-Raman spectra of Losartan have been recorded in the region 400–4000 cm−1. The spectra were interpreted in terms of fundamental modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by Quantum chemical methods. The vibrational frequencies yield good agreement between observed and calculated values. The infrared and Raman spectra were also predicted from the calculated intensities. (1)H and (13)C NMR spectra were recorded and resonance chemical shifts of the molecule were calculated. UV–Visible spectrum of the compound was recorded in the region 200–600 nm and the electronic properties HOMO and LUMO energies calculated by TD-HF approach. NBO atomic charges of the molecules and second order perturbation theory analysis of Fock matrix also calculated and interpreted. The geometrical parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities, and absorption wavelengths were compared with experimental and theoretical data of the molecule.

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