Solvent dependent study of carbonyl vibrations of 3-phenoxybenzaldehyde and 4-ethoxybenzaldehyde by Raman spectroscopy and ab initio calculations

A Raman spectroscopy investigation of the carbonyl stretching vibrations of 3-phenoxybenzaldehye (3Phbz) and 4-ethoxybenzaldeheyde (4Etob) was carried out in binary mixtures with different polar and nonpolar solvents. The purpose of this study was twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. Changes in wavenumber position, variation in the anisotropic shift and full width half maximum were investigated for binary mixtures with different mole fractions of the reference systems. In binary mixtures, the observed increase in wavenumber with solvent concentration does not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self-association of the solute. In all the solvents, a gradual decrease in the anisotropic shift reflects the progressive separation of the coupled oscillators with dilution. Gamma(i)(eta(c)), 3Phbz - solvent mixtures, exhibit a gradual decrease with decrease in the concentration of the solute which is an evidence on the influence of micro viscosity on linewidth. For 4Etob, the carbonyl stretching vibration shows two well-resolved components in the Raman spectra, attributed to the presence of two distinct carbonyl groups: hydrogen-bonded and free carbonyl groups. The intensity ratio of the carbonyl stretching vibration of these two types of carbonyl groups is studied to understand the dynamics of solute/solvent molecules owing to hydrogen bond interactions. Ab initio calculations were employed for predicting relevant molecular structures in the binary mixtures arising from intermolecular interactions, and are related to the experimental results. Copyright (C) 2009 John Wiley & Sons, Ltd.