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Alkene Reactions: Diiodide Formation using I2 and Alkenes

Iodine (I2) in the presence of alkenes reacts to form diiodides:

Alkene Reactions: Diiodide Formation using I2 and Alkenes image1.png

Iodine reacts with the alkene molecule to form a vicinal diiodide (1,2-diiodide) where iodines are added to the opposite side of each other in anti addition, giving 2 products that are enantiomers:

Anti Addition

Alkene Reactions: Diiodide Formation using I2 and Alkenes image4.png

Partial anti Addition

Alkene Reactions: Diiodide Formation using I2 and Alkenes image1.png

No stereocenters

Alkene Reactions: Diiodide Formation using I2 and Alkenes image2.png

The reaction mechanism is depicted below:

Alkene Reactions: Diiodide Formation using I2 and Alkenes image3.png

In the first step, electrons from the alkene bond react with the first iodine to make a bond, and electrons from the first iodine atom react with the other carbon to form another bond, forming a ring structure as an intermediate.

In the second step, the free, negatively charged iodine, attacks the backside of the intermediate structure, causing one iodine to finish with one type of stereochemistry and the other iodine to finish with the opposite type of stereochemistry, resulting in an anti addition..

The reagent used for this reaction is I2.