Give the expected products for the aldol condensations of (c) pentan-3-one.

Verified step by step guidance

1. Identify the alpha-hydrogens in pentan-3-one. Alpha-hydrogens are the hydrogens attached to the carbon atoms adjacent to the carbonyl group. In pentan-3-one, the alpha-hydrogens are on carbons 2 and 4.
2. Determine the enolate ion formation. Under basic conditions, one of the alpha-hydrogens is removed by a base, forming an enolate ion. The enolate ion is stabilized by resonance between the alpha-carbon and the carbonyl oxygen.
3. Perform the nucleophilic attack. The enolate ion acts as a nucleophile and attacks the carbonyl carbon of another molecule of pentan-3-one, forming a beta-hydroxyketone intermediate.
4. Dehydrate the beta-hydroxyketone. Under heating or continued basic conditions, the beta-hydroxyketone undergoes elimination of water (E1cB mechanism), forming an α,β-unsaturated ketone as the final product.
5. Write the final product structure. The product will be a conjugated enone, specifically 4-methylpent-3-en-2-one, resulting from the aldol condensation of pentan-3-one with itself.

Key Concepts

Aldol Condensation

Aldol condensation is a reaction between aldehydes or ketones that contain alpha-hydrogens, leading to the formation of β-hydroxy carbonyl compounds (aldols) followed by dehydration to yield α,β-unsaturated carbonyl compounds. This reaction is significant in organic synthesis as it allows for the formation of larger carbon skeletons and introduces functional groups.

Enolate Ion Formation

In aldol condensation, the first step involves the formation of an enolate ion from a carbonyl compound, which occurs when a base abstracts an alpha-hydrogen. This enolate ion acts as a nucleophile, attacking the carbonyl carbon of another molecule, leading to the formation of the aldol product. Understanding this step is crucial for predicting the products of the reaction.

Dehydration Reaction

After the aldol product is formed, it can undergo dehydration, where a molecule of water is eliminated, resulting in the formation of an α,β-unsaturated carbonyl compound. This step is essential as it stabilizes the product and enhances its reactivity, making it a key feature of aldol condensations. Recognizing the conditions that favor dehydration is important for predicting the final products.