Anti-Markovnikov Addition

Definition

Anti-Markovnikov addition is a type of electrophilic addition reaction that occurs when a hydrogen-containing molecule, such as water or hydrogen halide, adds to an alkene or alkyne in a way that places the hydrogen on the less substituted carbon. This is in contrast to the Markovnikov addition, which places the hydrogen on the more substituted carbon.

5 Must Know Facts For Your Next Test

1. Anti-Markovnikov addition is favored when the reaction mechanism involves the formation of a less stable carbocation intermediate.
2. Hydroboration-oxidation is an example of an anti-Markovnikov addition reaction, where borane adds to the less substituted carbon of the alkene.
3. Allylic bromination is another example of an anti-Markovnikov addition reaction, where a bromine atom is added to the carbon adjacent to the double bond.
4. Anti-Markovnikov addition is often used in organic synthesis to selectively functionalize alkenes and alkynes.
5. The anti-Markovnikov product is typically the kinetic product, while the Markovnikov product is the thermodynamic product.

Review Questions

• Explain how the mechanism of anti-Markovnikov addition differs from Markovnikov addition.
  • In anti-Markovnikov addition, the reaction mechanism favors the formation of a less stable carbocation intermediate, which leads to the addition of the hydrogen-containing molecule to the less substituted carbon of the alkene or alkyne. This is in contrast to Markovnikov addition, where the mechanism favors the formation of a more stable carbocation intermediate, resulting in the addition of the hydrogen-containing molecule to the more substituted carbon.
• Describe the role of anti-Markovnikov addition in the hydroboration-oxidation reaction of alkenes.
  • In the hydroboration-oxidation reaction, the borane (BH3) molecule adds to the alkene in an anti-Markovnikov fashion, forming an organoborane intermediate. This intermediate is then oxidized, resulting in the formation of an alcohol where the hydroxyl group is attached to the less substituted carbon. The anti-Markovnikov addition in this reaction is crucial for the selective functionalization of the alkene.
• Analyze how the concept of anti-Markovnikov addition is applied in the synthesis of organic compounds, particularly in the context of allylic bromination.
  • Anti-Markovnikov addition is an important tool in organic synthesis, as it allows for the selective functionalization of alkenes and alkynes. In the case of allylic bromination, a bromine atom is added to the carbon adjacent to the double bond, resulting in the formation of an allylic bromide. This anti-Markovnikov addition product is often a key intermediate in the synthesis of more complex organic molecules, as the allylic bromide can undergo further reactions, such as substitution or elimination, to introduce additional functional groups or modify the carbon skeleton.

Related terms

Markovnikov's Rule: Markovnikov's rule states that in an electrophilic addition reaction to an alkene, the electrophile adds to the carbon that can best stabilize the resulting carbocation intermediate.

Hydroboration-Oxidation: A two-step reaction where an alkene is first reacted with borane (BH3) to form an organoborane intermediate, which is then oxidized to form an alcohol.

Allylic Bromination: A radical substitution reaction where a bromine atom is substituted onto the carbon adjacent to the double bond of an alkene, forming an allylic bromide.