H Br-Br Br: Possible B mechanism? H @2004 Thomson-Brooks/Cole + :Br: :Br: C=C An alkene A bromonium ion +:Br: Top side open to attack :Br:- H Br H Br-Br :Br: Br Bottom side shielded from attack Cyclopentene Bromonium ion trans-1,2-Dibromo- intermediate cyclopentane