Allylic Bromination Continued

Pitfall

BrH can not always be used because it can form vicinal dibromides. This problem can be avoided by using N-Bromo Succinimide (NBS).

NBS does not form vicinal dibromides because it can only provide one bromine radical to the reaction.

(N-Bromo Succinimide)

Take Note

The stability of the carbon radicals is important. If there are more stable resonance structures, the mo lecule will change to the most stable structure before reacting with the radical bromine. This causes the formation of major and minor products.

Free Radical Stability

The stability of free radicals decreases from left to right. The alkene is the most stable due to its resonance structure. After the alkene, the most substituted carbon is the most stable.

Action