Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: sn1sn2e1e2 on April 15, 2014, 09:19:50 PM
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Which substance will react most rapidly with Br2 (aq)?
(A) Benzene
(B) Chloropropane
(C) Propanone
(D) Propene
I immediately eliminated A and C.
I know that B undergoes Sn2 reaction to form its enantiomer (and it's also very fast)
I know that D undergoes E2 which is also very fast.
I end up choosing B but the correct one is D.
How do I know whether substitution or elimination for this reaction occurs the fastest? Both do not seem to have any sterically hindered methyl groups.. and OH- is a pretty strong nuc/ base
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The question is what will react fastest with bromine. Why would propene, an alkene react fastest? In what way could a reaction take place?
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It is not an elimination reaction for D. It is the addition of bromine across the double bond.
Look at this website.
http://www.masterorganicchemistry.com/reaction-guide/bromination-of-alkenes-with-br2-to-give-dibromides/
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Sorry, I meant to put addition reaction :P
My guess is that propene establishes a more stable carbocation when a bromine atom is added on one side of the double bond?
For B Chloropropane, doesn't Sn2 reaction occur the fastest? (1 step process)
Adding across a double bond is a two step process..
I still can't see how D is the correct answer though
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You form a Bromonium ion. Not a carbocation. Look at the website.
In order to do the substitution it would have to be a bromide. Not molecular bromine. You can do what is called a Finkelstein reaction. React the chloropropane with sodium bromide in acetone and then reflux.
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D undergoes an elimination?……NOT favorable……
-Zack
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C would react, but it would need a catalyst.