Question

Bromination of cyclohexene under conditions given below yields :

• A.

  

• B.

  

• C.

  

• D.

  

Answer 1

The Correct Option is B

The bromination of cyclohexene is a reaction involving the addition of bromine (Br₂) across the carbon-carbon double bond in cyclohexene. This reaction typically proceeds through a halogenation mechanism that forms a vicinal dibromo compound. Here is the step-by-step reasoning and justification for the correct product:

1. Cyclohexene, a cycloalkene with one double bond, undergoes an electrophilic addition reaction with bromine.
2. The double bond in cyclohexene acts as a nucleophile and reacts with the electrophilic Br₂ molecule, forming a bromonium ion intermediate.
3. This intermediate is crucial because it guides the addition of the second bromine ion (Br^-) to the less hindered side of the bromonium ion, demonstrating regioselectivity of the reaction.
4. The result is the anti addition of bromine, meaning the bromine atoms are added to opposite sides of the former double bond.

The reaction product is thus 1,2-dibromocyclohexane. The correct answer based on the images given is the compound showing bromines on adjacent carbon atoms in an anti configuration.

This image shows the correct vicinal dibromo product of the bromination reaction of cyclohexene.

To further assist in recognizing such reactions, remember that:

• Electrophilic addition reactions typically form cyclic or open-chain intermediates prior to final product formation.
• Products are vicinal (on adjacent carbon atoms) in the case of typical alkene brominations.
• The stereochemistry is generally anti due to the mechanism involving a cyclic bromonium ion intermediate.