August 22, 2019, 01:13:12 AM
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Topic: Alkenes NBS stereochemistry?  (Read 182 times)

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Online sharbeldam

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Alkenes NBS stereochemistry?
« on: August 09, 2019, 12:15:18 PM »
So NBS react with alkenes with a bromine replacing an allylic hydrogen, but is there a stereochemistry to this reaction? I tried to look it up but didnt find anything regarding the stereochemistry, I know this reaction is radical, but would the Br be at same direction as the hydrogen that left, or can it enter from both places? would the product have the same configuration or opposite or would it be racemic mixture? if the carbon was chiral ofcourse.

Offline rolnor

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Re: Alkenes NBS stereochemistry?
« Reply #1 on: August 09, 2019, 05:15:51 PM »

Online sharbeldam

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Re: Alkenes NBS stereochemistry?
« Reply #2 on: August 09, 2019, 05:41:30 PM »
Not really, Im asking about the end result of that reaction, I know that carbocations are sp2, but when bromine attacks, it becomes a tetrahedral again, so im asking if the result would be same configuration or opposite or racemic...

Let's say it was R before the attack, would the product be S or R or Racemic

Offline rolnor

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Re: Alkenes NBS stereochemistry?
« Reply #3 on: August 09, 2019, 10:54:16 PM »
If the reaction goes via a non-chiral intermediate, how can the product be non-racemic?
« Last Edit: August 09, 2019, 11:47:23 PM by rolnor »

Online sharbeldam

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Re: Alkenes NBS stereochemistry?
« Reply #4 on: August 10, 2019, 04:23:08 AM »
Thank you :) I thought it would act like sn1,e1 (which undergo through non-chiral intermediate too) but had to be sure since its radical sp2.

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