Addition of Halogens to Alkenes ■ Bromine and chlorine add to alkenes to give 1,2-dihalides F2 is too reactive and 12 does not add Cl2 reacts as Cl+Cl,Br2 behaves similarly Br H H Br—Br Br H Br Br Cyclopentene trans-1,2-Dibromo- cis-1,2-Dibromo- cyclopentane cyclopentane (Sole product) (Not formed) 2004 Thomson-Brooks/Cole Reaction occurs with anti stereochemistry What is the mechanism? Addition of Halogens to Alkenes „ Bromine and chlorine add to alkenes to give 1,2-dihalides „ F 2 is too reactive and I 2 does not add „ Cl 2 reacts as Cl + Cl- , Br 2 behaves similarly „ Reaction occurs with anti stereochemistry What is the mechanism?