A Raman study of aqueous DMF and DMA solutions at low temperatures

Hydrogen bonding in aqueous N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) solutions was studied by Raman spectroscopy of the OH-stretching spectra of water as functions of solute concentration and temperature (from -50 to 50 degreesC). The Raman spectra were decomposed successfully into two components (the low- and high-frequency components). The peak area ratio of the low-frequency component to the high-frequency component increases exponentially with decreasing temperature. The frequency of the low-frequency component decreases linearly with lowering temperature down to -50 degreesC at all solute concentrations (solute mol fraction from 0.3 to 0.7). It is shown that the hydrogen bonds in the clathrate structures around DMA molecules are stronger than those around DMF molecules.