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Topic: regio/stereochemistry of electrophilic addn  (Read 3745 times)

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Offline BabeToluene

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regio/stereochemistry of electrophilic addn
« on: March 26, 2010, 05:25:38 PM »
Hey, guys!

I'm trying to understand the regio- and stereochemistry of the products that would form when the below reaction occurs and why they happen that way. So far, I'm convinced that there can be a case where the -OH points out of the page while the -CH3 and -Br point into the page. Is there anything else that can be displayed in the product?

Please post any of your thoughts and explanations. Thanks.


Offline bolo

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Re: regio/stereochemistry of electrophilic addn
« Reply #1 on: March 27, 2010, 08:08:34 AM »
Look at the TS where water as a weak nucleophile approaches C1 from the opposite side to brominium cation. It is because of more stable 3o pseudo-carbocation (C1) rather than 2o C2.



Finally you are obtained with two enantiomers of product.

Offline BabeToluene

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Re: regio/stereochemistry of electrophilic addn
« Reply #2 on: March 27, 2010, 09:10:43 PM »
Hmm. Based on your picture, are you saying that the Br was connected to C1 and C2 throughout some part of the mechanism? That would explain why they either both point out or both point in, opposite to the -OH.

Offline bolo

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Re: regio/stereochemistry of electrophilic addn
« Reply #3 on: March 28, 2010, 08:13:03 AM »
Yes. It is said to exist two enantiomeric forms of brominium ion and then an nuclophilic attack on 3o carbon occurs. It is somehow similar to ring opening of aziridines.


Offline BabeToluene

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Re: regio/stereochemistry of electrophilic addn
« Reply #4 on: March 28, 2010, 10:29:01 AM »
I see it now. Thank you both for your help.

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