Inhomogeneous distribution in methanol/acetone mixture: vibrational and NMR spectroscopy analysis

The main aim of this paper is to quantify the inhomogeneous distribution of the components of acetone/methanol mixture and to give detailed insight into the interplay between the dipole-dipole and hydrogen bonding interactions inducing this inhomogeneity. To this end, we used the concept of infrared excess molar absorption of a given vibrational mode as an observable which contains all the information on the collective interactions in the mixture. Indeed, the changes in the infrared excess molar absorption may be associated with the inhomogeneous distribution (clustering, self-association, or high-density domains) of the components and consequently with the interaction between the two components of the mixture. The results show that acetone molecules are not homogeneously distributed in the mixture, particularly in the mole fraction range of acetone between 0.05 and 0.55. The spectral signature of this inhomogeneity is associated with the appearance of a shoulder in the C═O and C-C stretching vibrational profiles of acetone. This inhomogeneity is driven by the prevalence of the dipole-dipole interactions over those of hydrogen bonding between acetone and methanol molecules. The inhomogeneous distribution of methanol molecules is found to occur in the mole fraction range of acetone between 0.55 and 1. In this case, the hydrogen bond interactions between methanol molecules prevail over those between methanol and acetone. However, the extent of this inhomogeneity is small compared with that of acetone in the low mole fraction range. The spectral signature of this inhomogeneity is not visible in the O-H stretching vibrational mode; however, a second peak appears as a shoulder of the C-O stretching vibrational mode in this range of acetone mole fraction.