Ochem: Br2,hv OR NBS,heat rxn

[A6project]

ethylbenzene reacts with Br2,hv or NBS,ROOR heat

This will creates Br- on more substituted carbon, right?


I have a question about this reaction. If ethylbenzene reacts with NBS,ROOR/heat, -Br doesn't go to the less substituted Carbon despite of the ROOR... but why????

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[TK2006]

ethylbenzene reacts with Br2,hv or NBS,ROOR heat

This will creates Br- on more substituted carbon, right?


I have a question about this reaction. If ethylbenzene reacts with NBS,ROOR/heat, -Br doesn't go to the less substituted Carbon despite of the ROOR... but why????

If you have ethyl benzene with NBS, you will get a benzylic halogenation as your major product. This is because of the high stability of the benzylic radical.

 

[A6project]

Sooo ROOR doesn't affect the reaction happening on the less substituted carbon? I guess I'm a little confused that ROOR might make it anti-markovnikov-ly

 

[rnbaxter]

Sooo ROOR doesn't affect the reaction happening on the less substituted carbon? I guess I'm a little confused that ROOR might make it anti-markovnikov-ly

The reaction undergoes a radical intermediate. Radicals are more stable on higher substituted carbons, in addition to the stabilization of this benzene molecule. These additional reagents, hv or NBS/and peroxide allow the radical formation. Therefore, indirectly allowing the anti Mark.

 

[Baylor2011]

Reactions which undergo a radical intermediate commonly go in the allylic or
benzyllic position, don't automatically go look for a tertiary carbon. Allylic and benzyllic are more stable.