What is the major product of bromination of anisole in ethanoic acid?a)o-Dibromobenzeneb)p-Dibromobenzenec)o-Bromoanisoled)p-BromoanisoleCorrect answer is option 'D'. Can you explain this answer?

Question

Answer

Phenyl alkyl ethers undergo bromination in the benzene ring with bromine in ethanoic acid. This due to the activation of benzene ring by OCH₃ group and its ortho, para directing effect. The para isomer is obtained in 90% yield.

Answer

Understanding Bromination of Anisole
Bromination of anisole in ethanoic acid primarily leads to the formation of p-bromoanisole due to the directing effects of the methoxy group (-OCH3) present in anisole.
Mechanism of Bromination
- Electrophilic Aromatic Substitution: Anisole undergoes bromination via an electrophilic aromatic substitution mechanism.
- Formation of Bromonium Ion: The bromine molecule (Br2) acts as an electrophile, leading to the formation of a bromonium ion.
Director Effects of the Methoxy Group
- Activating Group: The methoxy group is an electron-donating group, which activates the benzene ring.
- Ortho/Para Directing: It directs incoming electrophiles to the ortho and para positions relative to itself.
Product Distribution
- Preferred Position: While both ortho and para products can form, the para product (p-bromoanisole) is favored due to steric hindrance. The ortho position is more crowded, making the para position more favorable for substitution.
Conclusion
The major product of bromination of anisole in ethanoic acid is p-bromoanisole (option D). This outcome is a result of the methoxy group's activating and ortho/para directing effects, which lead to preferential substitution at the para position over the ortho position.

Answer

Understanding Bromination of Anisole
Bromination of anisole, an aromatic compound with a methoxy group (-OCH3) attached to a benzene ring, occurs in the presence of bromine in solvents like ethanoic acid. The methoxy group is an electron-donating group, which influences the position of bromination on the aromatic ring.
Mechanism of Bromination
- The electron-donating nature of the methoxy group activates the aromatic ring, making it more reactive towards electrophilic substitution.
- Bromine (Br2) acts as an electrophile. The methoxy group directs the incoming electrophile to the ortho (o-) and para (p-) positions relative to itself.
Position of Substitution
- The methoxy group stabilizes the intermediate carbocation formed during the reaction more effectively at the para position due to steric hindrance at the ortho position.
- Therefore, the substitution is predominantly favored at the para position.
Major Product Formation
- The major product of bromination in anisole is p-bromoanisole because:
- The para position is less hindered, allowing for easier access for the bromine.
- The stabilization of the carbocation intermediate is greater at the para position compared to the ortho position.
Conclusion
Thus, when anisole is brominated in ethanoic acid, the major product formed is p-bromoanisole, confirming option 'D' as the correct answer. This reaction exemplifies how substituents can greatly influence the site of electrophilic aromatic substitution.

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