IR study of hydrogen bonds in halogenoalcohol-water mixtures

The IR bending vibrational (v₂) band of the water molecules in aqueous haloethanol (XCH₂CH₂OH; X = Cl, Br, I) mixtures has been studied, and the haloethanols are found to give rise to red shifts of the v₂ band. Since the frequency of the v₂ band is reciprocally proportional to the hydrogen-bonding strength of water molecules, the results lead us to a conclusion that a breakdown of water structure occurs in the mixtures. The red shifts occur gradually in the whole range of the haloethanol concentrations, showing gradual breakdown of the water structure with an increase in the alcohol concentration. The effect of the alcohols on the red shift is found to be in the order ClCH₂CH₂OH < BrCH₂CH₂OH < ICH₂CH₂OH. The red shifts are discussed in comparison with the blue shifts of the v₂ band previously observed for the aqueous ethanol mixtures. The conclusion is consistent with that of the ¹H-NMR studies of the same mixtures in which the water structure is discussed in terms of the chemical shift of the water proton.