Halogenation of Alkenes Bromonium ion shields one side of molecule so that reaction with Br ion occurs only from opposite side Top side open to attack .e :Br :Br: B Bottom side shielded from attack Cyclopentene Bromonium ion trans-1,2-Dibromo- intermediate cyclopentane Bromonium ion shields one side of molecule so that reaction with Br￾ion occurs only from opposite side Halogenation of Alkenes