Three factors appear to affect n-alkane molecular vibrations in CHCl3/CCl4 solutions. These are: (1) Physical restriction of the νCH3 and νCH2 vibrations by solvent molecules. (2) Intermolecular hydrogen bonding between n-alkane protons and the free pair of electrons on Cl atoms of either CCl4 or CDCl3. The positively charged alkane protons arise during the dipole moment changes, δP/δQ, occurring during a full cycle of the νCH3 and νCH2 modes. (3) The physical restriction of solvent molecules, which is greater in the case of CDCl3 than in the case of CCl4 due to a high degree of CDCl3 orientation about n-alkane molecules due to repulsion of the C-D of CDCl3 by the n-alkane νCH3 and νCH2 protons, which allows stronger C-D:Cl bonds to be formed between solute and solvent.
R. A. Nyquist and S. L. Fiedler, "Infrared Study of n-Alkanes in CCl4, CDCl3/CCl4, and CDCl3 0.5% Solutions," Appl. Spectrosc. 47, 1670-1682 (1993)