The role of weak C–H···O hydrogen bond in alcohol–water mixtures

Abstract

Abstract Does the weak C–H···O hydrogen bonding interaction coexist in liquid when it competes with conventional hydrogen bonding interaction? The Raman spectroscopic studies were performed for deuterated 2‐propanol/water (CD 3 CHOHCD 3 ) mixture in the C‐H stretching region as a function of concentration and temperature. Combined with theoretical calculations, it is shown that both conventional O–H···O hydrogen bond and weak C–H···O hydrogen bond coexist in 2‐propanol/water solution and should be responsible for the observed C‐H blue shift in concentration‐dependent spectra. At relatively high alcohol concentrations, the O–H···O hydrogen bond plays a dominant role, whereas with the increase of water concentrations, the cooperative effect between C–H···O and O–H···O hydrogen bonds play a more significant role, responsible for continuously increased C‐H blue shift. Furthermore, the opposite temperature dependence was observed for the C‐H stretching spectra of 2‐propanol/water and methanol–water mixtures, which were explained as a result of the competition and balance between O–H···O and C–H···O hydrogen bonds at high temperature. The results not only show the role of secondary hydrogen bonds in the hydrated process of amphiphilic molecules but also demonstrate that the temperature can be used as a means of triggering and investigating weak C–H···O interaction in liquid.