Question

An enolate is a very strong nucleophile. Bromine is a strong electrophile, so it can react with much weaker nucleophiles. Give mechanisms for the reactions of bromine with cyclopentene and with phenol, which are both much weaker nucleophiles than an enolate.

Short answer

Bromine being a strong electrophile, participates in electrophilic addition with cyclopentene.

The double bond of the cyclopentenene attacks the bromine molecule to form a cyclic three-membered bromonium cation.

The cycling ring opens when the acts as a nucleophile and attacks from either above or below the plane resulting in two enantiomeric compounds.

Formation of two enantiomeric products

Step-by-step solution

Mechanism of bromine reacting with cyclopentene

Bromine being a strong electrophile, participates in electrophilic addition with cyclopentene.

The double bond of the cyclopentenene attacks the bromine molecule to form a cyclic three-membered bromonium cation.

The cycling ring opens when the acts as a nucleophile and attacks from either above or below the plane resulting in two enantiomeric compounds.

Formation of two enantiomeric products

Mechanism of bromine reacting with phenol

Bromine being a strong electrophile participates in electrophilic addition with

Phenol. When double bond attacks the bromine molecule resulting in the formation of a carbocation intermediate which is resonance stabilized. The resonating structures are given below.

Then the Br- will take the proton from the phenol ring to restore its aromaticity forming the final product 2-bromophenol.

Formation of 2-bromophenol