Reactivity of Enols:a-Substitution Reactions Acid-catalyzed a-halogenation (Cl2,Br2,and 12)of aldehydes and ketones is a common laboratory reaction a-Halogenation occurs in biological systems a-Halogenation of ketones in marine alga Br、 CH3 CH3 Br Br H Br Br From the Hawaiian alga Asparagopsis taxiformisAcid-catalyzed a-halogenation (Cl2 , Br2 , and I2 ) of aldehydes and ketones is a common laboratory reaction a-Halogenation occurs in biological systems ▪ a-Halogenation of ketones in marine alga Reactivity of Enols: α-Substitution Reactions