We have investigated the polarization dependence of FT-IR of the stretching of CD2 in chiral alkyl chain of TFMHxPOCBC-D2(4-(trifluoromethylhexy-3-d2 carbonyl) phenyl 4′-octyloxybiphenyl caboxylate) with a homeotropically aligned cell.It is found that the polarization dependence of Sm-C and that of Sm-CA are different.Simulation calculation indicates that the rotation of CD2 around the alkyl chain is hindered.