Local order and vibrational coupling of the C=O Stretching Mode of γ-Caprolactone in liquid binary mixtures

The isotropic and anisotropic parts Raman spectra of.-Caprolactone in the binary mixture at different concentrations have been measured. The non-coincidence effect (NCE) of gamma-Caprolactone was determined in carbon tetrachloride solution and DMSO solution. The NCE of the nu(11)(C=O) stretching mode in the gamma-Caprolactone/DMSO mixtures exhibits a linear plot, in contrast to that in the gamma-Caprolactone/CCl4 mixtures, which shows an upward (convex) curvature. The reduction and enhancement of the dimer structure (short-range orientational order) of.-Caprolactone in the gamma-Caprolactone/DMSO and gamma-Caprolactone/CCl4 mixtures respectively may play a major role in shifting of peak frequencies, thus the geometries of monomer and dimer of gamma-Caprolactone were calculated at the B3LYP-D3/6-311 G (d,p) level of theory. We proposed aggregated model to explain the gamma-Caprolactone C=O vibration NCE phenomenon and its concentration effect and found it largely consistent with our experimental findings. Solvent dependent experiment show the value of NCE declined with the increase of the solvent dielectric constant under the same condition which is consistent with the Logan's theory.