Organic Chemistry : Help with Keto-Enol Tautomerization

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #4 : Carbonyl Reactions

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

Possible Answers:

4-decyne

2-decyne

5-decyne

None of these answers

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 : Carbonyl Reactions

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:

III

IV

V

II

I

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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