Anti-Addition

Definition

Anti-addition is a type of organic reaction mechanism in which the incoming electrophile or nucleophile adds to the opposite side of the double bond, resulting in the formation of the opposite regioisomer compared to the typical addition reaction. This term is particularly relevant in the context of electrophilic addition reactions of alkenes, the hydration of alkenes via oxymercuration, and the reduction of alkynes.

5 Must Know Facts For Your Next Test

1. Anti-addition reactions occur when the incoming electrophile or nucleophile adds to the opposite side of the double bond, resulting in the formation of the opposite regioisomer compared to the typical addition reaction.
2. In electrophilic addition reactions of alkenes, anti-addition can lead to the formation of the anti-Markovnikov product, which is the opposite of the product predicted by Markovnikov's rule.
3. In the hydration of alkenes via oxymercuration, anti-addition can result in the formation of the anti-Markovnikov alcohol, where the hydroxyl group is attached to the less substituted carbon.
4. During the reduction of alkynes, anti-addition can occur, leading to the formation of the trans-alkene product instead of the cis-alkene product typically expected.
5. Anti-addition reactions are often influenced by steric and electronic factors, as well as the specific reaction conditions and the nature of the reactants involved.

Review Questions

• Explain how anti-addition can affect the regiochemistry of electrophilic addition reactions of alkenes.
  • In electrophilic addition reactions of alkenes, anti-addition can lead to the formation of the anti-Markovnikov product, which is the opposite of the product predicted by Markovnikov's rule. Typically, Markovnikov's rule states that the electrophile will add to the carbon that can best stabilize the resulting carbocation. However, in anti-addition, the electrophile adds to the opposite side of the double bond, resulting in the formation of the regioisomer that is not favored by Markovnikov's rule.
• Describe the role of anti-addition in the hydration of alkenes via oxymercuration.
  • During the hydration of alkenes via oxymercuration, anti-addition can occur, leading to the formation of the anti-Markovnikov alcohol. In this case, the hydroxyl group is attached to the less substituted carbon, rather than the more substituted carbon as predicted by Markovnikov's rule. The anti-addition is influenced by steric and electronic factors, as well as the specific reaction conditions, which can favor the formation of the anti-Markovnikov product over the Markovnikov product.
• Analyze how anti-addition affects the stereochemistry of the products in the reduction of alkynes.
  • In the reduction of alkynes, anti-addition can occur, leading to the formation of the trans-alkene product instead of the cis-alkene product typically expected. This is because the incoming hydrogen atoms add to the opposite sides of the triple bond, resulting in the trans stereochemistry of the final alkene product. The anti-addition is influenced by the specific reaction conditions, such as the reducing agent used, and can be an important factor in controlling the stereochemistry of the alkene products.

Related terms

Regiochemistry: The study of the positional selectivity of a reaction, which determines the location of the new bond formed.

Stereochemistry: The study of the spatial arrangement of atoms in a molecule and how it affects the molecule's properties and reactivity.

Markovnikov's Rule: A rule that predicts the regiochemical outcome of an electrophilic addition reaction, where the electrophile adds to the carbon that can best stabilize the resulting carbocation.