Hydrogen-bonding and self association investigated in the binary mixture (C6H5CN + CH3OH) via concentration dependent Raman study of the CN stretching mode of benzonitrile (C6H5CN) and ab-initio calculations

Abstract

The Raman study of (C₆H₅CN + CH₃OH) binary mixture has been presented. The isotropic part of the Raman spectra, I_iso are analyzed in the CN stretching region. For neat C₆H₅CN, the I_iso shows a double peak structure, which has been explained in terms of self association. A quantum chemical calculation on the optimized structures and wavenumbers of different modes of neat C₆H₅CN, self associated C₆H₅CN and the hydrogen-bonded C₆H₅CN⋯HOCH₃ complex reveals that the wavenumber position of the CN stretching mode is blue shifted due to both the self association and the hydrogen-bonding with CH₃OH. The Raman spectra of binary mixtures with different mole fractions of the reference system (C₆H₅CN), C = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, as well as neat liquid have been explained in terms of self association and hydrogen-bonding. A variation of intensity ratio of the peak assigned to the hydrogen-bonded complex to the main band with concentration exhibits a regular trend. The dephasing of the CN stretching mode in the free C₆H₅CN molecules seems to be governed predominantly by the concentration fluctuation model, but other effects like diffusion and motional narrowing may also have some small influence.