Influence of self-association and inter-molecular hydrogen bonding on the ν(C N) stretching mode of CH3C N and C2H5C N in binary mixtures with CH3OHA comparative study via concentration-dependent polarized Raman study andab initio calculation

Abstract

A Raman study of neat CH3C N and C2H5C N and their binary mixtures (CH3C N + CH3OH) and (C2H5C N + CH3OH) has been made using a scanning multichannel detection technique, which is also more precise, especially when the observed Raman line profile has multiple components. The spectra in the ν(C N) stretching region (2220–2280 cm−1) for both the reference systems were recorded with varying mole fractions of the reference molecule, CH3C N/C2H5C N, from 0.9 to 0.1. Ab initio calculations on the optimized structure and wavenumber position of the ν(C N) stretching mode of neat CH3C N and C2H5C N and their self-associated and hydrogen-bonded complex reveal that the wavenumber position of the ν(C N) stretching mode is shifted towards higher Raman wavenumbers because of both self-association and the hydrogen-bonded complex. This shift has been explained in terms of the repulsive interaction between the solute and solvent molecules. The dephasing of ν(C N) stretching mode with concentration shows that the viscosity dependent contribution is much more prominent than that due to concentration fluctuation. Copyright © 2006 John Wiley & Sons, Ltd.