taninipanini
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Currently studying for my Organic Chemistry exam and I came upon a question that is pretty basic yet I'm having trouble figuring it out. i'll do my best to write it into words.
Which intermediate completes the reaction scheme below?
2-bromo-3-methyl butane reacts with NaOH yielding an intermediate that is unknown which reacts with Br2 and H20 creating 2-methyl-2-hydroxy-3-bromo-butane (?) I'm not sure if I named that properly. Its a four carbon chain with a methyl and OH on the second carbon and a Br on the third.

My question is, what is the intermediate?

Update: here's a picture of the question. I know that the answer is A, but I dont understand why it isnt D
Attachment 709780
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Pigster
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No attachement.

Are you sure your product is correct? It would be named 3-bromo-2-methylbutan-2-ol.

But making that from your starting point using the chemicals you've stated would be tricky (unless people know some chemistry I don't: which is likely).

You could eliminate the Br to 2-methylbut-2-ene, and then addition to that with Br2 producing the 3-bromo-2-methylbutan-2-ium carbocation. Which in theory could react with OH- forming your product. That would at least follow Markovnikov.
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EierVonSatan
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(Original post by Pigster)
You could eliminate the Br to 2-methylbut-2-ene, and then addition to that with Br2 producing the 3-bromo-2-methylbutan-2-ium carbocation. Which in theory could react with OH- forming your product. That would at least follow Markovnikov.
Pretty much this, the strong alkali would eliminate the HBr to form an alkene, followed by electrophilic addition :yep:
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ChemistryWebsite
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(Original post by Pigster)
No attachement.

Are you sure your product is correct? It would be named 3-bromo-2-methylbutan-2-ol.

But making that from your starting point using the chemicals you've stated would be tricky (unless people know some chemistry I don't: which is likely).

You could eliminate the Br to 2-methylbut-2-ene, and then addition to that with Br2 producing the 3-bromo-2-methylbutan-2-ium carbocation. Which in theory could react with OH- forming your product. That would at least follow Markovnikov.
(Original post by EierVonSatan)
Pretty much this, the strong alkali would eliminate the HBr to form an alkene, followed by electrophilic addition :yep:
Agreed. Elimination to give the alkene first, followed by further reaction to give the final product.
The question describing that alkene as an "intermediate" could be misleading as that word usually means something else in organic mechanisms.
It's a shame we don't know the conditions of the suspected dehydration reaction, that would help clarify.
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taninipanini
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(Original post by TutorsChemistry)
Agreed. Elimination to give the alkene first, followed by further reaction to give the final product.
The question describing that alkene as an "intermediate" could be misleading as that word usually means something else in organic mechanisms.
It's a shame we don't know the conditions of the suspected dehydration reaction, that would help clarify.
Name:  Screen Shot 2017-12-09 at 3.28.54 PM.png
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taninipanini
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(Original post by Pigster)
No attachement.

Are you sure your product is correct? It would be named 3-bromo-2-methylbutan-2-ol.

But making that from your starting point using the chemicals you've stated would be tricky (unless people know some chemistry I don't: which is likely).

You could eliminate the Br to 2-methylbut-2-ene, and then addition to that with Br2 producing the 3-bromo-2-methylbutan-2-ium carbocation. Which in theory could react with OH- forming your product. That would at least follow Markovnikov.
I tried to reupload the attachment. Not sure if it worked though!Name:  Screen Shot 2017-12-09 at 3.28.54 PM.png
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Pigster
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(Original post by taninipanini)
picture
That worked.

I had named it (2-methylbut-2-ene) now all you have to do is match the name to the answer A-D.
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taninipanini
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(Original post by Pigster)
That worked.

I had named it (2-methylbut-2-ene) now all you have to do is match the name to the answer A-D.
Thanks for all of your help so far! I'm still somewhat confused as to why D isn't formed via the mechanism that I drew and attached.Name:  IMG_1181.jpg
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I've identified that the answer is A but could you possibly draw the mechanism and arrow pushing showing that result? Sorry for all of the trouble
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Pigster
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(Original post by taninipanini)
Thanks for all of your help so far! I'm still somewhat confused as to why D isn't formed via the mechanism that I drew and attached.

I've identified that the answer is A but could you possibly draw the mechanism and arrow pushing showing that result? Sorry for all of the trouble
What level are you working at? A level (if so which spec)? 1st year degree?

Your mechanism is just SN2, which wouldn't put the Br on the 3 position.
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taninipanini
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(Original post by Pigster)
What level are you working at? A level (if so which spec)? 1st year degree?

Your mechanism is just SN2, which wouldn't put the Br on the 3 position.
I'm an Undergraduate student studying in the U.S. as a bioengineering major. This is for an organic chemistry course we are required to take.

Thank you for all your help. I understand where I went wrong, thanks!
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