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In present study, the experimental and theoretical harmonic vibrational frequencies of gliclazide molecule have been investigated. The experimental FT-IR (400-4000 cm(-1)) and Laser-Raman spectra (100-4000 cm(-1)) of the molecule in the solid phase were recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) have been calculated using ab initio Hartree Fock (HF), density functional theory (B3LYP hybrid function) methods with 6-311++G(d,p) and 6-31G(d,p) basis sets by Gaussian 09W program. The assignments of the vibrational frequencies were performed by potential energy distribution (PED) analysis by using VEDA 4 program. Theoretical optimized geometric parameters and vibrational frequencies have been compared with the corresponding experimental data, and they have been shown to be in a good agreement with each other. Also, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies have been found., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The purpose of this study is to investigate the vibrational spectrum of tolbutamide byab initiotechniques in combination with experimental studies. The Fourier transform infrared spectra (400–4000 cm−1) and Laser-Raman spectra (100–4000 cm−1) of tolbutamide have been obtained in the solid phase. Assignments have been found by the combination of the vibrational frequencies and the contribution of the potential energy distributions. Assignments have been compared with the theoretical and experimental results of similar structures as reported in the literature. Structural parameters such as bond lengths and angles, frequencies and infrared intensities and Raman activities of tolbutamide have been computed by density functional theory and Hartree–Fock methods using 6–311G++(d,p) and 6–31G(d) basis sets. The computed vibrational frequencies and optimized structural parameters are consistent with the corresponding experimental results. In addition, the images of tolbutamide frontier molecular orbitals (highest occupied and lowest unoccupied) and its energy gaps have been interpreted with the assistance of quantum chemical calculations. [ABSTRACT FROM PUBLISHER]