Scaled Quantum Chemical Studies of the Molecular Structure and Vibrational Spectra of Minoxidil

Abstract

The Fourier transform Raman and Fourier transform infrared spectra for minoxidil have been recorded in the region 4000—100 cm⁻¹ and 4000—450 cm⁻¹, respectively. The structural and spectroscopy data of the molecule in the ground state were calculated by using density functional theory methods with 6-311G (d, p) basis set. A detailed vibrational analysis of the title compound has been done using normal coordinate analysis following the scaled quantum mechanical force field methodology. The calculated molecular geometry parameters and scaled vibrational wavenumbers are well compared with the experimental data. The electronic properties, such as excitation energies, absorption wavelength, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energies were performed by time-dependent density functional theory approach, and the results are in good agreement with experimental absorption spectrum. The charge delocalizations of these molecules have been analyzed using natural bond orbital analysis. The molecule orbital contributions are studied by density of energy states. Fukui functions, local softness, and electrophilicity indices for selected atomic sites of the title compound are determined. Finally, the thermal behaviors of the compound have been calculated by different temperature.

Keywords:

• density functional theory
• natural bonding orbital
• normal coordinate analysis
• potential energy surface

Acknowledgments

This paper was presented at The Fourth International Conference on Perspectives in Vibrational Spectroscopy (ICOPVS 2013) which was held at Bishop Moore College, Mavelikara, Kerala, India, August 6–9, 2013 and was invited to be published in Spectroscopy Letters by special editor Dr. D. Sajan of the Department of Physics, Bishop Moore College, Mavelikara, Kerala, India.

Notes

^a Abbreviations: ν, stretching; β, in plane bending; g, out of plane bending; t, torsion; ss, symmetric stretching; as, asymmetric stretching; trig, trigonal deformation; wag, wagging; ro, rocking; sci, scissoring; tw, twisting; sym, symmetric deformation; asym, asymmetric deformation; vs, very strong; s, strong; m, medium; w, weak; vw, very weak.

^b Relative absorption intensities normalized with highest peak absorption equal to 100.

^c Relative Raman intensities calculated by Eq. [1] and normalized to 100.

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