Solution dynamics in aqueous monohydric alcohol systems

The associative behavior of aqueous methanol, ethanol, and tert-butyl alcohol solutions at mole fractions ranging from 0 to 1 at 273, 283, and 298 K was examined using PGSE NMR measurements of the self-diffusion coefficients of the alkyl group, water and, depending on the exchange rate, hydroxyl protons. The results show that tert-butyl alcohol has the greatest ability to stabilize water through hydrophobic hydration than methanol or ethanol due to the more ideal fit of the tert-butyl group to the structure of water. However, at higher concentrations tert-butyl alcohol is the least able to cohesively interact with water through hydrogen bonding. The results provide compelling evidence for alcohol self-association (methanol < ethanol < tert-butyl alcohol) in very dilute solution. The alcohol molecules can be likened to very short lipid molecules undergoing complicated solution interactions due to their amphiphilic nature.