Question

Explain Aldol condensation of ethanal.

Hint:

Aldol condensation requires \( \alpha \)-hydrogen; dehydration yields conjugated products.

Answer 1

Aldol condensation involves the reaction of two aldehyde molecules (with \( \alpha \)-H) in the presence of a base to form a \( \beta \)-hydroxy aldehyde, which may dehydrate to an unsaturated aldehyde. For ethanal (\( \chemfig{CH_3-CHO} \)): \[ 2 \chemfig{CH_3-CHO} \xrightarrow{\text{dil. NaOH}} \chemfig{CH_3-CH(OH)-CH_2-CHO} \xrightarrow{-\text{H}_2\text{O}} \chemfig{CH_3-CH=CH-CHO}. \] Step 1: Enolate ion forms from one ethanal, attacking the carbonyl of another, forming 3-hydroxybutanal (aldol).

Step 2: Dehydration yields crotonaldehyde (\( \chemfig{CH_3-CH=CH-CHO} \)).