Organic Chemistry : Help with Keto-Enol Tautomerization

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Keto Enol Tautomerization

Which of the following results in a single ketone product following acid catalyzed hydration?

Possible Answers:

4-decyne

None of these answers

5-decyne

2-decyne

3-decyne

Correct answer:

5-decyne

Explanation:

During acid catalyzed hydration, a hydroxy group replaces one of the bonds in the triple bond and a double bond is formed. This is called an enol. The enol naturally turns into a ketone in a process called tautomerization. The hydroxy group can attach to either carbon across the double bond, and naming is done so that substituents have the lowest numbers. Only on 5-decyne will result in a single product, as no matter which carbon the hydroxy group bonds to, it is still on carbon 5. Thus, the only final product is 5-decone.

The other answer options will still react, but will form multiple products due to lack of symmetry.

Example Question #2 : Help With Keto Enol Tautomerization

What is the product of the reaction shown?

Screen shot 2015 11 15 at 12.19.05 pm

Screen shot 2015 11 15 at 12.19.15 pm

Possible Answers:

I

II

III

V

IV

Correct answer:

IV

Explanation:

First step: bromination across the double bond

Second step: double dehydrohalogenation and removal of terminal alkyne hydrogen

Third step: neutralization of the molecule

Fourth/fifth step: hydroboration/oxidation, followed by keto/enol tautomerization

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