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

Author Institution: 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 CH$_3$ 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 CH$_3$ group of acetonitrile. The length of H-bond N...H-O is 2,21 A, and for H$_2$C - 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 CH$_3$ group of acid is preserved also in dimer "acetonitrile - acetic acid"

INTERMOLECULAR INTERACTION IN LIQUID CHLOROFORM AND ITS SOLUTIONS. NON-EMPIRICAL CALCULATIONS AND RAMAN SPECTRA

Author Institution: Samarkand State University. 703004 Samarkand, University blvd 15, Uzbekistan; Samarkand State University. 703004 Samarkand, University blvd 15, Uzbekistan; Samarkand State University. 703004 Samarkand, University blvd 15, Uzbekistan; Samarkand State University. 703004 Samarkand, University blvd 15, UzbekistanIt was studied Raman spectra of C-H and C-D vibrations of chloroform and its solution with acetonitrile. It was found that in pure chloroform the band maxima frequency noncoincidance in parallel and perpendicular polarized components of Raman spectra line. Difference is 1.8 cm-1 for chloroform and 1.5 cm-1 for deuteried chloroform. At dilution in neutral solvent this frequence difference is decreased. The results was explained by molecular aggregation in pure liquid, when for monomers and aggregates correspond two near placed and overlapping bands with different values of depolarization ratio. The calculations on base of DFT method (B3LYP) show that the such aggregations formation in liquid is possible, at this in dimmer the hydrogen atom of C-H band of one molecule is oriented to one of three atoms chlorine of other molecule of chloroform. The frequency difference of monomer and dimer vibrations is 2 cm-1. In mixture with acetonitrile the bands C-H and C-D are experienced high frequency shift in comparison with place of band in pare liquid, at this the band with concentration change go through maximum that indicates about band complexity in mixtur

STUDY OF STRUCTURAL FLUCTUATIONS IN AQUEOUS SOLUTIONS OF ACETIC ACID BY LIGHT SCATTERING METHODS

Author Institution: Department of Physics, The Ohio State University; Department of Physics, Samarkand State UniversityTwo maxima of isotropic Rayleigh light scattering intensity for acetic acid-water solutions at 20 0C are observed at 0.06 and 0.12 mole fraction contents of acid. These maxima with temperature increasing is decreased. $C=O$ vibrations band in Raman spectrum at contents of acid below 0.06 mole fraction has simple shape, whereas at above contents this band is complicated and consists of several lines. These date indicate about the changes of aggregated formations in mixture with concentration