Reaction Catalyzed by NBS

The steps in the reaction mechanism are shown below. The net reaction for allyhc bromination with NBS produces neither bromine nor the by-product hydrogen bromide. 

Write the structures of all products formed in the allylic bromination of 2-hexene, using IM equivalent of NBS. 

Free radical bromination of the following compound using IM equivalent of NBS gives one allylic bromo compound, (a) Write the structure of a second possible isomeric product, (b) Explain why it 

The reaction with NBS generates two resonance structures one is secondary (I), the other is tertiary (II). 

The difference in stabihties of secondary and tertiary free radials is not as large as the difference between second and tertiary carbocations because the carbon atom that has the unpaired electron is less electron deficient. Thus, the stability of the double bond in the product is important. Adding bromine at the tertiary center gives a trisubstituted double bond, but bromination of the secondary allylic center gives a tetrasubstituted double bond, which is more stable. And, that is the major product. 

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