Pressure-enhanced C-H•••O interactions in aqueous tert-butyl alcohol

We have investigated pressure-enhanced C-H...O interactions in tent-butyl alcohol (TBA)/D2O mixtures. On the basis of its responses to changes in pressure and concentration, TBA appears to be the ideal candidate to study the variations in structural and dynamical properties of C-H...O interactions. For dilute aqueous TBA, the pressure dependence of the C-H bands yielded blue frequency shifts at pressures below 0.3 GPa, but an increase in pressure leads to a red frequency shift at pressures above this value. This discontinuity in frequency shift is related to enhanced C-H...O interactions. The frequency of the C-H stretching modes that characterize C-H...O hydrogen bonding undergoes a blue shift with pressure. This behavior is in contrast with the general trend of red shifts observed in strongly hydrogen-bonded systems that occur through O-H...O and C=O...H interactions. We discuss the results of density functional theory calculations that predict the frequency shift of the C-H stretching vibrations.