Allylic bromination of alkanes using NBS

by James

Description: When treated with N-bromosuccinimide (NBS) and light (hν) alkyl groups adjacent to alkenes will be converted into alkyl bromides.
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{ 12 comments… read them below or add one }

Ola

In the subject of this post you have written alkanes and these are, I think alkenes.

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DIVYA

what is the reagent used in allylic bromination of CH3CH2CH=CH2

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james

NBS, just like in this example.

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Remo

Hey I think you are wrong because in the third and fourth reaction from top you forgot allylic rearrangement

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james

Good point! This should be updated to reflect the potential for allylic rearrangement.

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Raj

Hey from where exactly are you getting the HBr

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james

The dirty secret with this reaction is that it works best with slightly impure NBS, which contains HBr.

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remo

In the subject of this post you have written alkanes and these are, I think alkenes.

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James

I chose “alkanes” because it’s an alkyl (sp3) carbon which is being brominated but I should probably just remove the “alkanes” part and keep it as “allylic bromination”. : – )

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Frederick Karayan

Greetings! I have found your Oxidation Ladder, part of your Org 2 study sheets to be invaluable. I have “added” allylic bromination to your oxidation ladder. You should definitely add it into a future version.

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James

Hi Frederick – thanks for writing and I’m very glad you found that sheet useful – it’s one of my favorites. I agree that allylic bromination is an oxidation but I wasn’t sure where to put it in the oxidation ladder that would make sense in the context of other reactions. For instance one could do an elimination to make a diene, but there are no dienes on the sheet. So I left it off in the name of simplicity. Where did you add it, if you don’t mind me asking?

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Felipe

I couldn’t understand very well if 1 mole of NBS will give me, in theory, 1 mole of brominated product. Besides, will I get only 0.5 moles of brominated product when I use pure bromine (due to the formation of HBr)? Any help would be appreciated.

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