Question

Question: Draw a stepwise mechanism for the following reaction.

Short answer

Answer

Mechanism:

Step-by-step solution

N-bromosuccinimide

N-bromosuccinimide is utilized for “selective halogenation” at the allylic carbon, i.e., C-H bond, in the presence of light.

Mechanism 

Initiation:

In the presence of light, a weak Na-Br bond is NBS is homolytically cleaved, and the bromine radical is formed.

Initiation reaction

Propagation and Termination:

The bromine radical formed in the initiation step and a proton is abstracted from the C-H bond, and an allylic radical is formed. This radical can undergo resonance.

The allylic radical reacts with Br₂ to form the C-Br bond.

The propagation step can occur multiple times.

When two radicals combine, a stable product is formed, which terminates the reaction.

Propagation and termination reactions