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Keywords:

  • hydrogen bonding;
  • self-association;
  • binary mixture [(CH3CH2CHO + H2O/CH3OH)];
  • polarized Raman study;
  • DFT calculations

Abstract

The Raman spectra of neat propionaldehyde [CH3CH2CHO or propanal (Pr)] and its binary mixtures with hydrogen-donor solvents, water (W) and methanol (M), [CH3CH2CHO + H2O] and CH3CH2CHO + CH3OH] with different mole fractions of the reference system, Pr varying from 0.1 to 0.9 at a regular interval of 0.1, were recorded in the ν(C[DOUBLE BOND]O) stretching region, 1600–1800 cm−1. The isotropic parts of the Raman spectra were analyzed for both the cases. The wavenumber positions and line widths of the component bands were determined by a rigorous line-shape analysis, and the peaks corresponding to self-associated and hydrogen-bonded species were identified. Raman peak at ∼1721 cm−1 in neat Pr, which has been attributed to the self-associated species, downshifts slightly (∼1 cm−1) in going from mole fraction 0.9 to 0.6 in (Pr + W) binary mixture, but on further dilution it shows a sudden downshift of ∼7 cm−1. This has been attributed to the low solubility of Pr in W (∼30%), which does not permit a hydrogen-bonded network to form at higher concentrations of Pr. A significant decrease in the intensity of this peak in the Raman spectra of Pr in a nonpolar solvent, n-heptane, at high dilution (C = 0.05) further confirms that this peak corresponds to the self-associated species. In case of the (Pr + M) binary mixture, however, the spectral changes with concentration show a rather regular trend and no special features were observed. Copyright © 2010 John Wiley & Sons, Ltd.