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INTERMOLECULAR H-BONDS IN ACETONITRILE AND ITS SOLUTIONS. RAMAN SPECTRA AND AB INITIO CALCULATIONS.

A. JUMABAEV, F. H. TUKHVATULLIN, H. HUSHVAKTOV AND A. ABSANOV, Samarkand State University, 15, University blvd., Samarkand, 703004, Uzbekistan.

\noindent The band of CN vibrations in pure acetonitrile in Raman spectra is located at 2254 cm^-1, and it is asymmetric in low-frequency region. In mixture with acetic acid we observed appearance of a band of aggregations of acetonitrile molecules with those of acetic acid in high-frequency region. Relative intensity of the band increases with decreasing concentration of acetonitrile.

\noindent Calculations showed that in monomer molecule of acid one of H atoms of CH₃ group participates in formation of weak intramolecular H-bond with = O atom. Length of this bond is 2,55 A. For monomer molecule interaction of = O atom with H atom of O - H group also takes place. Optimized model of dimer "acetonitrile - acetic acid" represents closed aggregation with H-bond between N atom and H atom of O-H group. Moreover, there is a possibility of formation of intramolecular H - bond between = O atom of acid and one of H atoms of CH₃ group of acetonitrile. The length of H-bond N...H-O is 2,21 A, and for H₂C - H ... O is 2,61 A. Energy profit in this case is 5,3 kcal/mole. Weak intramolecular H-bond between O atom of C = O group and one of H atoms of CH₃ group of acid is preserved also in dimer "acetonitrile - acetic acid".