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Effects of dipole interaction and solvation on the Cdouble bond; length as m-dashO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements
Authors:Yukiteru Katsumoto   Takeyuki Tanaka   Yukihiro Ozaki  Shinzo Hosoi
Affiliation:aDepartment of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan;bIntegrated Center for Sciences, Ehime University, Matsuyama 790-8566, Japan;cSchool of Science and Technology, Kwansei Gakuin University, Sanda 669-1337, Japan;dSchool of Pharmaceutical Sciences, Kyushu University of Health and Welfare, Nobeoka 882-8508, Japan
Abstract:The concentration dependence of the Cdouble bond; length as m-dashO stretching (νCdouble bond; length as m-dashO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl4 has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the νCdouble bond; length as m-dashO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the νCdouble bond; length as m-dashO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the νCdouble bond; length as m-dashO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl4 solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the νCdouble bond; length as m-dashO band observed in a highly diluted CCl4 solution (≤0.023 M) indicate that the solvation effect of CCl4 is more complicated than those of cyclohexane and n-hexane. The analyses of the νCdouble bond; length as m-dashO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.
Keywords:N,N-Dimethylacetamide   Infrared spectroscopy   Isotropic and anisotropic Raman spectra   Noncoincidence effects   C  http://www.sciencedirect.com/scidirimg/entities/dbnd"   alt="  double bond   length as m-dash"   title="  double bond   length as m-dash"   border="  0"  >O stretching band   Nonpolar solvents
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