Question

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

Answer 1

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).

(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.

By analogy, I predict that 4-methylbenzaldehyde with cyclopentanone will form
(`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