Electronic structure and vibrational spectra of common pain killer (Aspirin and Ibuprofen) in gas phase and different medium: An ab initio and DFT approach

Abstract

The molecular geometries of common pain killer drugs Aspirin and Ibuprofen have been investigated using ab initio quantum chemical calculations at the Restricted Hartree-Fock (RHF) and the Density functional method at the Becke3LYP (B3LYP) level by employing 6-31+G*basis set in gas phase, water, methanol and ethanol. The structure, dipóle moments, vibrational frequencies with IR intensities and other thermodynamic properties have also been studied. It is found that both Aspirin and Ibuprofen molecules are relatively more stable in water. A tentative assignment of the intense infrared calculated frequencies (IR) for both Aspirin and Ibuprofen corresponding to the different modes has been carried out. The observed IR spectra of these molecules were also recorded in the range 4000-400 cm.