The structure of aqueous solutions of tertiary butanol

Abstract

Using neutron diffraction with isotopic substitution, the structures of aqueous solutions of tertiary butanol have been studied as a function of concentration. As the behaviour of this system is thought to be driven by hydrophobic interactions, particular attention was paid to the hydration of the non-polar headgroups and the nature of the intermolecular contacts. As concentration is increased from 0.06 to 0.16 mole fraction tertiary butanol, there is evidence for the growth of small clusters of the alcohol molecules, with butanol-butanol coordination of two to three even at the lowest concentration. Orientational pair correlation functions show that the dominant intermolecular contacts between alcohol molecules are between the non-polar head groups, as would be expected for a system driven by hydrophobic interactions. As concentration increases, however, there is evidence of mixed polar-non-polar contacts. The alcohol group's hydrogen bonding requirements appear to be fully met by polar contacts with water molecules: there is no evidence for significant butanol-butanol hydrogen bonding.