NMR AND RAMAN-SPECTROSCOPIC STUDY OF CDCL3 IN CYCLOHEXANE SOLUTIONS IN THE PRESENCE OF PYRIDINE, QUINUCLIDINE OR TRIETHYLAMINE

NMR and Raman spectroscopic methods have been used to study deuterated chloroform (ca. 10 mol%) with added pyridine (py), quinuclidine (Q) or triethylamine (Et3N) (0 - ca. 15 mol%) in cyclohexane solutions. In the Raman spectra of the CDCl3 solutions new bands shifted to lower wavenumbers appear for the C-Cl and C-D stretching vibrations when the above N-donor Lewis bases are added. These bands are ascribed to the formation of 1:1 hydrogen bonded complexes with CDCl3. A quantitative evaluation of the band areas, using the breathing mode of cyclohexane as internal standard, allowed relative molar scattering coefficients to be evaluated for the displaced C-Cl bands of the CDCl3 hydrogen bonded species by fitting calculated to experimental concentrations. Equilibrium constants were then obtained for the 1:1 complex formations CDCl3 + N-donor half arrow left over half arrow right CDCl3.N-donor: K(py) = 0.8 +/-0.2, K(Q) = 0.8 +/- 0.2, and K(Et3N) = 0.53 +/- 0.05 dm3 mol-1. The NMR relaxation times of 2D and Cl-35 for CDCl3 have been measured and analyzed in terms of anisotropic rotational diffusion, in addition the perpendicular rotational diffusion constant of CDCl3 in cyclohexane has been estimated from the Raman C-D stretching band widths. Using the concentrations of the free and hydrogen bonded CDCl3 species from the Raman experiment the rotational correlation times for the CDCl3.N-donor complexes have been obtained.