Organic Chemistry : Help with Aldol Condensation

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Aldol Condensation

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Determine the major product of the given intramolecular aldol reaction.

Screen shot 2015 07 07 at 8.30.53 pm

Possible Answers:

None of these

II

III

IV

I

Correct answer:

II

Explanation:

Keep in mind the following principles: Cyclization is favored when a five/six-member ring may be formed. Addition at an aldehyde is favored relative to the same reaction at a ketone. 

As a result, abstraction of a hydrogen bound to carbon 6 (an alpha-carbon) is favored since the resulting carbanion may attack the aldehyde (carbon 1) to form a six-member ring, resulting in compound II. Compound I results from abstracting a hydrogen from carbon 2, generating a carbanion which may then attack the ketone. Based on the latter of the above principles, this is a minor product.

Example Question #2 : Help With Aldol Condensation

What is the final organic product of the reaction shown?

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Screen shot 2015 11 13 at 2.54.56 pm

Possible Answers:

IV

V

II

I

III

Correct answer:

I

Explanation:

First step: Friedel-Crafts acylation of benzene

Second step: Formation of enolate

Third step: aldol addition (enolate attacks carbonyl carbon in benzaldehyde)

Fourth step: neutralization of anion and dehydration forming alkene

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