IR spectra simulation as auxiliary tool for gas chromatography/Fourier transform IR spectroscopy/mass spectrometry identification of unknown compounds. 2. PM3, AM1, MNDO and MINDO3 simulations for simple nitriles

A set of the semi-empirical methods (PM3, AM1, MNDO and MINDO3) supplied by the HyperChem™ package has been tested to find the best auxiliary tool for the gas chromatography/Fourier transform IR spectroscopy/mass spectrometry identification of nitriles, taking 23 relatively simple nitriles as test compounds. Of the four methods, MNDO can be considered as the most advantageous since: (1) for 17 compounds of 23 tested, the IR spectra simulated by this method best match the experimental spectra (and in additional 3 cases, the results are as good as those obtained by AM1 method); (2) within the range of experimental wavenumbers of 900–3100 cm⁻¹, MNDO provides the best linearity between the calculated and experimental values (with a correlation coefficient of 0.989). A scaling factor of 0.85 can be used to afford better correspondence between the calculated and experimental wavenumbers. A disadvantage of the MINDO simulations is underestimation of ν_CN (and sometimes ν_CH) band intensities.