Interpretation of the IR spectrum of d-limonene by molecular modeling methods

The article presents structural and dynamic models of conformers of the (+)-limonene molecule optimized to a minimum of total energy. According to Boltzmann statistics, the most probable structure of the (+)-limonene molecule at room temperature has been calculated in the form of three naturally occurring conformations. The fundamental oscillation frequencies of functional groups and atoms of (+)-limonene conformations in the form of a theoretical infrared spectrum were calculated using the density functional theory DFT with a hybrid three-parameter B3LYP functional based on the 6-31G(d,p) basis. This spectrum was interpreted by comparing the absorption band frequencies in the experimental infrared spectrum of (+)-limonene and the fundamental oscillation frequencies of the parts of the (+)-limonene molecule. A comparative analysis of the theoretical and experimental spectra has been carried out in order to prove the validity of the model of molecular dynamics used.