Q6P - Organic Chemistry (Mcmurry)

Question

The major product of the reaction of methylenecyclohexane with N-bromosuccinimide is 1-(bromomethyl)cyclohexene. Explain.

Step-by-Step Solution

Answer

1-(Bromomethyl)cyclohexene is the major product of this reaction, because the reaction is occurring at the primary end of the allylic radical. As a result, a product with a trisubstituted double bondis formed.

Step 1: Allylic bromination

It is the hydrogen replacement on a carbon adjacent to a double bond or aromatic ring with bromine. Unsymmetrical alkenes forms a mixture of products after allylic bromination.

Step 2: Allylic bromination of methylenecyclohexane

In this reaction, the two product formed are not in equal proportions. The reaction at the two ends is not equal because of the formation of a unsymmetrical allylic radical. Thus, the reaction at the primary end (which is less hindered) is favoured. This is the reason, we get 1-(Bromomethyl)cyclohexene as a major product.

                      Mechanism of allylic bromination of methylenecyclohexane