Hydrogen bonding in methanol—organic solvent and methanol—water mixtures as studied by the vco and voh
1982; Elsevier BV; Volume: 81; Issue: 1-2 Linguagem: Inglês
10.1016/0022-2860(82)80077-x
ISSN1872-8014
AutoresRaman Bands, G. Käbisch, K. Pollmer,
Tópico(s)Spectroscopy and Chemometric Analyses
ResumoAt low concentrations of methanol in non-polar organic solvents, a splitting of the CO Raman band into monomeric and polymeric components has been observed. From a study of the interactions of CH3OH monomers with proton-donor and proton-acceptor molecules, it is found that vCO decreases upon H bonding via the lone pairs while it increases upon bonding via the OH proton, and that vco is more sensitive to the latter type of interaction. The frequency shifts of the polymeric component upon dilution are associated with a shortening of methanol chains, the extent of which differs in CCl4 and CHCl3, solution. The cooperative properties of H bonding are clearly reflected both in the voh and vCO band shapes. In methanol—water mixtures a decrease in the CO frequency is observed, accompanied by a gradual removal of the splitting in the IXXX — I⊥ peak positions. This, together with the increase in the H2O bending frequency, indicates, that methanol—methanol hydrogen bonds are progressively replaced by intercomponent bonds to water, mainly via the lone pairs of CH3OH. The excess of lone pairs, introduced by the alcohol component, causes an increase in the overall strength of the H bonds in the mixtures and creates a significant fraction of free lone pairs at the water oxygen atoms.
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