Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: rlabomba on December 07, 2017, 10:28:37 AM
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Had this on my test last week and i'm drawing a blank. I said BR2 with light but wouldn't that attach at the Pi bond carbon?
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You would want to use a reagent that gives a low concentration of bromine, what could that be?
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NBS?
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Yes, that is the usual reagent for allylic bromination.
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@OP,
Do you know how the mechanism for this is different from the addition of bromine across a double bond?
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Yes, that is the usual reagent for allylic bromination.
I was watching a video and the video showed Br2 will accomplish the same reaction by adding the Br to the carbon adjacent to the double bonded carbon. Is this true?
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@OP,
Do you know how the mechanism for this is different from the addition of bromine across a double bond?
I know with NBS the Br will attach to the adjacent Carbon of the double bond, the Br radical will grab the Hydrogen to the adjacent double bond and will form a secondary radical on the substrate. Then the Br will bond to this carbon. Am I saying this right?
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You certainly have the key idea correct: allylic bromination is a radical process, unlike the addition across a double bond, which is a polar process. Your description of the second portion of the radical process is unclear to me. The carbon-centered radical reacts with a fresh molecule of Br2, and creates a fresh bromine radical.