A procedure for obtaining IR, Raman and NMR spectra of organic compounds by means of quantum mechanical calculations with the ORCA-5.0.3 software

Abstract

This manuscript describes a procedure for the estimation of IR, Raman, and NMR (¹H and ¹³C) spectra of organic species using quantum-mechanical calculations to show undergraduate university students the implementation of simulation techniques in the elucidation of their molecular structures. Avogadro-1.2.0 (Hanwell et al., 2012) and Orca-5.0.3 (Neese, 2018) software were used for the elaboration of this procedure. This study shows that the harmonic vibrational frequencies and the signal intensities estimated for the Infrared spectra were acceptable and in correspondence with the experimental values. In contrast, the intensities of the Raman spectrum presented considerable deviations that can be attributed to the approach used for the estimation of the intensities of the spectrum and performing the quantum-mechanical calculations in the vacuum for the selected molecules. Instead, the signals from the ¹H and ¹³C NMR spectra were obtained with a very good estimate based on the reported RMSE values.