What is the product of the aldol condensation between cyclopentanone and 4-methylbenzaldehyde?

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Dec 26, 2015

Answer:

The product is probably (#2E,5E#)-2,5-bis(4-methylbenzylidene)cyclopentanone.

Explanation:

The aldol condensation involves attack of an enolate ion on the base of a carbonyl compound to form a β-hydroxycarbonyl compound (an aldol).

Aldol condensation
(from www.chem.ucla.edu)

The aldol can then dehydrate to form an α,β-unsaturated carbonyl compound.

The process requires an active methylene adjacent to a carbonyl group.

If there are two active methylenes, the condensation can occur on each side of the carbonyl group.

For example, benzaldehyde with acetone gives dibenzalacetone.

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By analogy, I predict that 4-methylbenzaldehyde with cyclopentanone will form
(#2E,5E#)-2,5-bis(4-methylbenzylidene)cyclopentanone.

(2E,5E)-2,5-bis(4-methylbenzylidene)cyclopentanone

The #E,E# isomer should be more stable because the steric interactions of the ortho hydrogens with the #"H"# atoms on the cyclopentane ring are smaller than those with the carbonyl oxygen

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