Structural optimization and vibrational analysis of an antidiabetic drug: tolbutamide

Abstract

The purpose of this study is to investigate the vibrational spectrum of tolbutamide by ab initio techniques 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.