Spectroscopic studies of water—aprotic-solvent interactions in the water-rich region

Abstract

Although the fundamental infrared spectrum for HOD in D₂O in the O—H stretching region shows little change as basic aprotic solvents such as dimethylsulphoxide or dimethylformamide are added, the first overtone (2ν_OH) shows a marked fall in the 7120 cm^–1 band normally assigned to “free” O—H oscillators. This is interpreted in terms of hydrogen bonding to the base resulting in scavenging of free O—H groups.

N.m.r. studies of the water proton resonance on adding such basic cosolvents show little change or a small down-field shift in the 0–0.05 mole fraction region prior to an upfield shift which is a function of the basicity of the cosolvent. This region of insensitivity is explicable in terms of the scavenging of the free OH groups detected by overtone infrared spectroscopy. The concepts of water structure making and breaking are discussed in the light of these results.