The wavenumbers of peaks of parallel and perpendicular polarized components of the C O vibration band for dimethylformamide in the Raman spectra differ by 14.5 cm −1 . The difference in wavenumber values decreases and falls to zero on strong dilution with CCl 4 and dimethyl sulfoxide. A doublet structure of the band is observed in solutions with CCl 4 in the 0.2 mole fraction concentration region. The abovementioned non-coincidence of C O vibration band wavenumbers in pure liquid is explained by the complexity of the band, i.e. the presence within the band of two close and overlapped lines with different magnitudes of depolarization ratio belonging to monomeric molecules (high wavenumber) and aggregate formation. In a mixture at strong dilution there remains only one type of formation, and the band acquires a simple shape of a separate line, and the above-mentioned wavenumber difference falls to zero. The experimental results are supplemented by ab initio calculations of normal vibrational wavenumbers and of some parameters for monomeric and dimeric dimethylformamide molecules.

No abstract

No abstract

Experimental studies of the Raman scattering of the band of C = O vibrations of acetone (1710 cm–1) showed that the parallel and perpendicular polarized components have a large half-width (respectively, 11.6 and 18 cm–1) and also the bands' maxima of these components are shifted by ~5 cm–1. In the neutral solvent (heptane), the difference of the maxima position of the bands decreases. Calculations showed that the molecules of acetone can aggregate to form a dimer with the energy gain of 10.1 kJ/mole. In the dimer several hydrogen bonds are formed between the oxygen atom of one molecule and the hydrogen atoms of CH3 -group of another molecule. In an aqueous mixture of acetone, according to calculations, there is a possibility for formation of dimers and closed trimer aggregates with the energy gain, respectively, 19.1 and 45.8 kJ/mole. Calculation showed that symmetric and antisymmetric O–H vibrations of water are displaced in the interaction with acetone to lower frequencies, respectively, to 3808.4 and to 3931.8 –1.

No abstract