Experimental and computational analysis of C≡N and C–H stretching bands in acetonitrile solutions

Raman and FTIR spectra of pure acetonitrile (ACN) and its solutions with water, dimethyl sulfoxide (DMSO) and formamide were investigated experimentally and by means of computer simulation. The research is focused on the C≡N and C–H stretching vibrations of H-bonded complexes in the solutions. Potential energy distribution analysis was carried out for obtained vibrational frequencies. Experiments reveal a blue shift of the C≡N and C–H stretching bands for ACN dissolved in water. In DMSO solutions, the frequencies of these bands were almost unchanged, only their intensity changed. In formamide solution, the C≡N stretching band is blue-shifted, and the C–H stretching vibration band is slightly red-shifted. It is estimated that the main reason for this is weak hydrogen bonds or van der Waals interaction of C–H⋅⋅⋅O and N⋅⋅⋅H–O types. This viewpoint is supported by the results of atom in molecule, non-covalent interaction, and reduced density gradient analyses.