The Fourier transform infrared (4000–400 cm-1 ) and Fourier transform Raman (3500–50 cm-1 ) spectra of Ketotifen were recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers were investigated with the help of density functional theory (DFT) method using B3LYP/6-31G (d,p) as basis set. The observed vibrational wavenumbers were compared with the calculated results. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Predicted electronic absorption spectra from TD-DFT calculation have been analyzed comparing with the UV–Vis (200–800 nm) spectrum. The HOMO–LUMO energy gap explains the charge interaction taking place within the molecule. The Chemical reactivity and chemical potential of Ketotifen is calculated. In addition, molecular electrostatic potential (MEP), analysis were investigated using theoretical calculations.
