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Topic: Wohl Ziegler reaction  (Read 2609 times)

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Offline kirushanth

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Wohl Ziegler reaction
« on: August 05, 2012, 09:46:22 AM »
In allylic bromination using NBS, why is that low concentration substitutes in allylic position?

Offline discodermolide

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Re: Wohl Ziegler reaction
« Reply #1 on: August 05, 2012, 10:30:22 AM »
In allylic bromination using NBS, why is that low concentration substitutes in allylic position?

Have a look here:
http://www.organic-chemistry.org/namedreactions/wohl-ziegler-reaction.shtm
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Offline camptzak

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Re: Wohl Ziegler reaction
« Reply #2 on: August 05, 2012, 02:18:33 PM »
would it do something different in high concentration of NBS?

it seems like the allylic position is the most readily attacked due to resonace stabilization.
but maybe in higher concentrations Br radical attack the allylic position and then there is still some Br2 left to attack the double bond?

and then maybe if there really a great molar excess of Br2 with hv initiation the bromine radicals would start ripping hydrogens off the carbon chain?
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Offline discodermolide

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Re: Wohl Ziegler reaction
« Reply #3 on: August 05, 2012, 02:21:13 PM »
would it do something different in high concentration of NBS?

it seems like the allylic position is the most readily attacked due to resonace stabilization.
but maybe in higher concentrations Br radical attack the allylic position and then there is still some Br2 left to attack the double bond?

and then maybe if there really a great molar excess of Br2 with hv initiation the bromine radicals would start ripping hydrogens off the carbon chain?


A quote from the link "It is very important to keep the concentration of Br2 and HBr low to prevent side reactions derived from simple ionic addition with the alkene."
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