Binary diol-water systems studied by 17O nuclear magnetic resonance spectroscopy.: Interpretation of the effect of diol structure on 17O-water chemical shift.: Formation of networks of water molecules stabilized by weak C-H...O interactions

The chemical shift for O-17-labeled water in binary diol-water systems shows two types of dependency on mole fraction, determined by the structure of the diol. Type I behavior consists of a single component which is substantially linear and monotonic in the upfield direction with increasing diol concentration and independent of temperature. Type II behavior is biphasic with an initial downfield component which is strongly temperature dependent occurring for glycol mole fractions <0.20, followed at mole fractions greater than or equal to0.20 by a linear component which may be in either the upfield or downfield direction. analogous to type I behavior. Type II behavior seems to be associated exclusively with diols containing a terminal methylcarbinol group, CH3CH(OH)-, at least for the series of diols studied in this paper. The initial downfield component caused by this group is interpreted in terms of water structuring and the formation of a clathrate-like cage involving 10-15 water monomers stabilized by weak hydrogen bonds around the methylcarbinol group.