Iodination of alkenes to give vicinal diiodides (1,2-diiodides)
Description: Treatment of alkenes with iodine (I2) leads to the formation of vicinal diiodides (1,2-diiodides).
Notes: The iodides add to opposite faces of the double bond (“anti addition”)
Mechanism: Attack of the alkene on iodine gives the iodonium ion (Step 1, arrows A and B). The iodonium ion is then attacked by iodide ion at the most substituted carbon where applicable (Markovnikoff) to give the 1,2-diiodide.