Raman spectra and ab initio calculation of a structure of aqueous solutions of methanol

• Published in: Journal of molecular structure 2017-03, Vol.1131, p.25-29
• Main Authors: Hushvaktov, H.A., Tukhvatullin, F.H., Jumabaev, A., Tashkenbaev, U.N., Absanov, A.A., Hudoyberdiev, B.G., Kuyliev, B.
• Format: Article
• Language: English
• Subjects: Alcohol-water mixtures; H-aggregates; Hydrogen bond; Polarized components; Raman spectra
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2016.10.061

Small amount of low molecular weight alcohols leads to appearance of some special properties of alcohol-water solutions. In the literature it is associated with structural changes in solution with changing concentration. However, the problem special properties and structure of solutions at low concentration of alcohol is not very clear. Accordingly, we carried out quantum-chemical calculations and experimental studies of aqueous solutions of methyl alcohol. The calculations performed for ten molecular alcohol-water mixtures showed that with a low concentration of methyl alcohol in water the solubility of alcohol is poor: the alcohol molecules are displaced from the water structure and should form a particular structure. Thus, with low concentration of alcohol in the aqueous solution there are two types of structures: the structure of water and the structure of alcohol that should lead to the presence of specific properties. At high concentration of alcohol the structure of water is destroyed and there is just the structure made of alcohol-water aggregates. This interpretation is consistent with the experimental data of Raman spectroscopy. The band of CO vibrations of alcohol is detected to be of complex character just in the region of the presence of specific properties. Formation of intermolecular H-bonds also complicates the Raman spectra of OH or O-D vibrations of pure alcohol: a non-coincidence of peak frequencies, a shift of the band towards low-frequency region, a strong broadening of the band. •Special properties appear in low-concentrated aqueous solution of methyl alcohol.•Alcohol molecules in water form a special structure.•Complicated lines of CO vibration are observed in Raman spectra near special point.•H-bonding leads to complication of alcohol's OH and O-D vibration in the aggregate.