Under basic conditions, acetaldehyde self-aldol condensates; which is the major dehydrated product?

Master NCEA Level 3 Organic Chemistry Reaction Schemes. Prepare with multiple choice questions, complete with hints and detailed explanations. Ace your exam with our comprehensive tools!

Multiple Choice

Under basic conditions, acetaldehyde self-aldol condensates; which is the major dehydrated product?

Explanation:
When acetaldehyde reacts under basic conditions, it first forms its enolate and adds to another molecule of acetaldehyde, giving a β-hydroxyaldehyde (the aldol adduct). This intermediate readily loses water to form an α,β-unsaturated aldehyde. The dehydration is driven by conjugation with the aldehyde and by forming the more stable trans (E) geometry for the double bond. Therefore the major dehydrated product is crotonaldehyde (trans-2-butenal). The β-hydroxyaldehyde is the immediate aldol product, not the dehydrated one, and there is no reason for formation of 1,3-butadiene in this simple acetaldehyde self-condensation.

When acetaldehyde reacts under basic conditions, it first forms its enolate and adds to another molecule of acetaldehyde, giving a β-hydroxyaldehyde (the aldol adduct). This intermediate readily loses water to form an α,β-unsaturated aldehyde. The dehydration is driven by conjugation with the aldehyde and by forming the more stable trans (E) geometry for the double bond. Therefore the major dehydrated product is crotonaldehyde (trans-2-butenal). The β-hydroxyaldehyde is the immediate aldol product, not the dehydrated one, and there is no reason for formation of 1,3-butadiene in this simple acetaldehyde self-condensation.

More practice questions