December 05, 2021, 09:46:25 AM
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Topic: E2 stereoslectivity and regiochemistry  (Read 219 times)

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Offline jylarai

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E2 stereoslectivity and regiochemistry
« on: November 20, 2021, 02:56:57 AM »
Hello,

I have a question regarding two substrates which are presented in this imgur link below. (d) and (g) which are the two substrates marked in red. Why does (d) have only regioselectivity but G has both regioselectivity and stereoslectivity? From my understanding, regioselectivity occurs when two beta carbons have different protons that are not identical and if you are a using a small base, the zaitsev is the major product which is more substituted than the Hoffman which is the minor and less substituted. And stereoslectivity occurs when there are two protons on a beta carbon with the trans being major and cis being minor. I don't understand mainly how (g) has stereoslectivity
 
https://imgur.com/a/T3v85BY, this is the picture

Offline Babcock_Hall

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Re: E2 stereoslectivity and regiochemistry
« Reply #1 on: November 20, 2021, 08:41:54 AM »
I cannot see (g).  Is there supposed to be a second image?  What do you know about the geometry of the transition state for a typical E2 process?  Is there a special rule?
« Last Edit: November 20, 2021, 09:13:06 AM by Babcock_Hall »

Offline jylarai

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Re: E2 stereoslectivity and regiochemistry
« Reply #2 on: November 20, 2021, 10:13:42 AM »
I cannot see (g).  Is there supposed to be a second image?  What do you know about the geometry of the transition state for a typical E2 process?  Is there a special rule?


(G) is a 3-bromo-3-methylpentane reacted with t-buOK. In this case, I understand that the major product should be the less substituted alkene due to the sterically hindered base. I think I may figure out why (d) only has regioselectivity, it's because if you drew either the cis and trans isomer for (d), they are identical

Offline Babcock_Hall

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Re: E2 stereoslectivity and regiochemistry
« Reply #3 on: November 20, 2021, 01:22:58 PM »
In (d) cis-trans isomerism is not possible.

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