C-H···O Interaction in Methanol-Water Solution Revealed from Raman Spectroscopy and Theoretical Calculations.

A combination of temperature-dependent Raman spectroscopy and quantum chemistry calculation was employed to investigate the blue shift of CH3 stretching vibration in methanol-water mixtures. It shows that the conventional O-H···O hydrogen bonds do not fully dominate the origin of the C-H blue shift and the weak C-H···O interactions also contribute to it. This is consistent with the temperature-dependent results, which reveal that the C-H···O interaction is enhanced upon increasing the temperature, leading to further C-H blue shift in observed spectra at high temperature. This behavior is in contrast with the general trend that the conventional O-H···O hydrogen bond is destroyed by the temperature. The results will shed new light onto the nature of the C-H···O interaction and be helpful to understand hydrophilic and hydrophobic interactions of amphiphilic molecules in different environments.