Non-coincidence effect in methyl ethyl ketone: a solvent-dependent Raman study

Abstract

The wavenumber shift of the isotropic and anisotropic profiles of the C O stretching mode of methyl ethyl ketone (MEK) was measured in several polar and non-polar solvents at different concentrations. The anisotropy shift function F = dn .2e + n 2 / 2 e −1 was plotted as a function of solute concentration (f). A discontinuity around 50% appears to be present in many solvent systems. The variation of shift with concentration may arise as a result of several interactions such as dipole-dipole, dipole-quadrupole, quadrupole-quadrupole and higher multipole interactions in the solute-solvent systems. The plot of lnF against f is linear over the entire range. It may be inferred from the data that repulsive-type intermolecular forces play a significant role in these molecular systems. The steric effects may be responsible for the discontinuity in the F vs f plot apart from the atomic quadrupole effects and other intermolecular forces.

Concentration-dependent frequency shifts of the CS stretching modes in ethylene trithiocarbonate studied by Raman spectroscopy

“…The Raman measurements were performed at room temperature (293 K) and atmospheric pressure. In all the runs, we used the same integration time of 100 s and the same accumulations number (20) for all different concentrations to improve the signal-to-noise ratio. The spectral intensity of each mixture was constantly checked against that of the neat liquid normal species, and whenever necessary, the integration time was slightly varied to recover the same initial intensity condition of the latter.…”

“…These effects lead to the spectral change of both the isotropic and anisotropic Raman components of the reference vibrational mode of solute molecule. [18][19][20][21] This phenomenon of the isotropic and anisotropic Raman bands (and also the IR band in some cases) of the same vibrational mode that appear at different frequency positions can be called noncoincidence effect (NCE). The peak frequency shifts of both the isotropic and anisotropic Raman spectra with the change of reference molecule concentration provide useful information regarding the solute-solvent interaction and intermolecular forces.…”

“…The chemical dilution of the reference molecule is an effective method to break the liquids structure and modify the local chemical interactions. These effects lead to the spectral change of both the isotropic and anisotropic Raman components of the reference vibrational mode of solute molecule . This phenomenon of the isotropic and anisotropic Raman bands (and also the IR band in some cases) of the same vibrational mode that appear at different frequency positions can be called noncoincidence effect (NCE).…”