5 旋光异构 C2H5 <Br cr 文H 8 CH3 (2S,3R)-3-氯-2-溴戊烷 CH3 CH3 H CHO HO CHO HO H CIii H CH3 CH3 C2H5 C2H5 R s s R CH3 CH3 H I一 C2H5 C2H5 H s HO CHO CH3 H C H CH3 C2 H5 I R S S R CHO HO CH3 H C H CH3 C2 H5 I C2 H5 Cl H Br CH3 H （2S，3R）-3-氯-2-溴戊烷 S S C2 H5 I H CH3 H CH3 C2 H5 I 5 旋光异构