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Topic: Enol-Ketone Tautomerization, OR?  (Read 4342 times)

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Offline bluefairy1

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Enol-Ketone Tautomerization, OR?
« on: April 15, 2014, 06:17:26 PM »
Hello to whoever reads this. Thank you so much for your time.

I just had a test today and there was a question that asked to show what the product was of a reaction  of 2-cyclohexen-1-ol with H3O+ (If I counted the ring right). I asked a TA at the Chemistry aid room, and they said it was a keto-enol tautomerisation. However, I believed it to be a Hydration reaction. I say its is a hydration under the reasoning that the -OH group is a whole 2 C's apart from the double bond. Does anyone know what it could possibly be? Could you possibly explain why too? I don't need the "answer" per-se, just knowledge as to which reaction it is.

I've attached an image of the reaction (because I have to get to class and don't have time to read how to make it in the forum software. :< ). Thanks so much!

Offline discodermolide

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Re: Enol-Ketone Tautomerization, OR?
« Reply #1 on: April 15, 2014, 07:46:09 PM »
Well it's definitely not keto-enol tautomerisation.
What other reactions do alcohols undergo in the presence of acid?
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Offline orgopete

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Re: Enol-Ketone Tautomerization, OR?
« Reply #2 on: April 15, 2014, 08:31:15 PM »
The TA could have been correct, but the structure of the reactant would have to be different. If it were cyclohex-1-en-1-ol, this could tautomerize.
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Offline bluefairy1

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Re: Enol-Ketone Tautomerization, OR?
« Reply #3 on: April 15, 2014, 09:54:25 PM »
@discodermmolide: Let me give some more background on what happened. This was an "extra-credit" test worth 15 pts. We had our exam on Friday of last week and the average was very low so on Monday the teacher said he wanted to give an extra credit quiz to bring up the average. He said the quiz would be on the material from the exam. That material covered alkenes+reactions & alkynes+reactions. On the same day (monday) he introduced SN1 SN2 and said "we'll be going into E1 E2 as well!" We never actually "did" anything with it really. Today was the extra credit quiz. I was thinking maybe it would be an SN1 SN2, E1, or E2. I'm feeling its an elimination rather than a substitution though. And if that's the case , I'm wondering how he could reasonably test us on this material.

@orgopete: Yeah I know what you mean. I was thinking it would have to be that too, but it wasn't which is why I was so perplexed. I tried doing a hydration but that didn't seem right either.

Offline discodermolide

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Re: Enol-Ketone Tautomerization, OR?
« Reply #4 on: April 15, 2014, 10:02:54 PM »
What about elimination of water? What'd compound would that give?
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Offline bluefairy1

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Re: Enol-Ketone Tautomerization, OR?
« Reply #5 on: April 15, 2014, 10:10:11 PM »
Gosh. We really haven't learned anything about this yet but I'm going to give it a stab in the dark. Is it possibly 1,3-cyclohexene? Or something benzene like?
(Looking at my textbook elimination isn't until a whole chapter after the one we're starting right now).

Offline sn1sn2e1e2

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Re: Enol-Ketone Tautomerization, OR?
« Reply #6 on: April 15, 2014, 10:30:48 PM »
I don't think the reaction is a keto-enol  tautomerisation because there is no vinylic OH on the double bond.

Offline bluefairy1

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Re: Enol-Ketone Tautomerization, OR?
« Reply #7 on: April 15, 2014, 10:40:24 PM »
@sn1sn2e1e2: I know what you mean. And it can't be a hydration because the products would be too unstable then and would just undo the reaction. So I think discodermolide is correct in that it is an elimination. I'm just waiting to see if my answer of 1,3-cyclohexene is right or not. I think it is, based off of this sheet I found on the internet, but I'm not 100% sure:
https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/alcohol1.htm
under the subheader "3. Elimination Reactions of Alcohols"

Offline discodermolide

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Re: Enol-Ketone Tautomerization, OR?
« Reply #8 on: April 15, 2014, 11:46:01 PM »
Yes a cyclohexadiene:
C1=CCCC=C1

cyclohexa-1,3-diene
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Offline orgopete

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Re: Enol-Ketone Tautomerization, OR?
« Reply #9 on: April 15, 2014, 11:49:40 PM »
With the info provided, I call this exhibit one why ochem gets a bad reputation. If this were an alkene reaction, the product would be an alcohol. One generally doesn't indicate aqueous acid for dehydration/elimination. If you do, expect confusion, in my opinion.

I might expect formation of an allylic carbocation, but in water, it should add water back to it. No net reaction. The only other reaction I might think of is a neighboring group addition of water to the alkene. Were reactions of this type given in class or problems? If so, I might expect a three-membered ring intermediate. Opening of this ring would give a trans-1,2-diol.
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