Direct observation of hydrophobic interactions in aqueous solutions of organic compounds by supercooling and enthalpies of mixing

Supercooling temperatures and enthalpies of mixing with some solvents have been examined for two kinds of solutions subjected to different thermal treatments (solutions I and II) of tetrahydrofuran (THF), isopropyl alcohol (2-PrOH), and ethyleneglycol butylether (BE), and ethyleneglycol isobutylether (i-BE) in order to observe more directly the structural organization of water molecules around a nonpolar molecule in an aqueous solution. For THF and 2-PrOH solutions, supercooling temperatures of solution I were found to be 2–3 degrees higher than those of solution II, and differences H_I-H_II were found to be about 3 kJ mol^–1. It has been concluded that these results directly reflect the difference in the stability of hydrogen-bonded water networks in an aqueous solution.