Hydrogen bonding in CHCl3/DMSO-d(6) and CDCl3/DMSO-h(6) mixtures

Raman and IR spectra of solutions of CHCl3/DMSO-d(6) and CDCl3/DMSO-h(6) (DMSO dimethyl sulfoxide) solutions are presented and analyzed in terms of hydrogen-bonding interactions. In the region of the C-H stretch of CHCl3 or the C-D stretch of CDCl3, addition of DMSO causes 3 new band to appear which is broadened and red-shifted with respect to the free C-H or C-D stretch. We postulate that this new band derives from chloroform hydrogen-bonded to DMSO and compare the relative intensities of the bands due to complexed and free chloroform to the ratio of the concentrations of the two species, calculated according to published equilibrium constants. It is concluded that complexation leads to considerable enhancement of the inherent Raman and infrared intensities of the C-H and C-D stretch. The vibrational spectra reveal evidence that both 1:1 and 2:1 (2 chloroform to 1 DMSO) complexes form and that the intensity enhancement of the C-H or C-D stretch is larger for the first than the second hydrogen bond. The general features of the hydrogen-bonded C-H and C-D stretch are compared to those of other hydrogen-bonded systems, and possible explanations for the intensity enhancement are considered.