NMR AND FT-IR STUDIES OF HYDROGEN-BONDS IN ETHANOL-WATER MIXTURES

H-1- and C-13-NMR measurements of ethanol(EtOH)-water mixtures were carried out using an external reference method at different temperatures to discuss hydrogen-bonding interactions present in the mixtures. FT-IR measurements of the same mixtures were also carried out for this purpose. It is found that the water proton resonance shifts to low field in the water-rich region, remains almost unchanged up to ca. 60 mol % of EtOH, and then shifts again gradually to low field with further increase in EtOH concentration. From FT-IR measurements, the bending vibrational band of the water is found to shift to high frequency with increasing EtOH concentration. The frequency shift has a concentration dependence similar to that of the water proton chemical shift. These findings differ markedly from the results of 1H-NMR measurements using the internal reference method reported so far. The significant low-field shifts of the water proton in the water-rich region are interpreted in terms of strengthening of the hydrogen bonds formed among water molecules surrounding the alkyl group of EtOH, while the gradual low-field shifts in the EtOH-rich region are attributed to the formation of strong hydrogen bonds between the water hydrogen and the hydroxyl oxygen of self-associated EtOH aggregates.