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The product formed in Aldol condensation is
A
a beta-hydroxy aldehyde or a beta-hydroxy ketone
B
an alpha-hydroxy aldehyde or ketone
C
an alpha, beta unsaturated ester
D
a beta-hydroxy acid
Detailed Solution
Aldehydes and ketones having at least one $\alpha$-hydrogen atom, in the presence of dilute alkali, give a $\beta$-hydroxy aldehyde (aldol) or a $\beta$-hydroxy ketone (ketol).
The base removes an $\alpha$-hydrogen to form a carbanion (enolate), which attacks the carbonyl carbon of a second molecule.
$CH_3-CHO + H-CH_2-CHO \xrightarrow{dil.\ NaOH} CH_3-CH(OH)-CH_2-CHO$ (aldol, 3-hydroxybutanal)
The OH group is on the $\beta$-carbon with respect to the carbonyl group.
On heating, the aldol loses water to give an $\alpha,\beta$-unsaturated aldehyde: $CH_3-CH(OH)-CH_2-CHO \xrightarrow{\Delta,\ -H_2O} CH_3-CH=CH-CHO$ (crotonaldehyde)
So the product formed in aldol condensation is a beta-hydroxy aldehyde or a beta-hydroxy ketone.
The base removes an $\alpha$-hydrogen to form a carbanion (enolate), which attacks the carbonyl carbon of a second molecule.
$CH_3-CHO + H-CH_2-CHO \xrightarrow{dil.\ NaOH} CH_3-CH(OH)-CH_2-CHO$ (aldol, 3-hydroxybutanal)
The OH group is on the $\beta$-carbon with respect to the carbonyl group.
On heating, the aldol loses water to give an $\alpha,\beta$-unsaturated aldehyde: $CH_3-CH(OH)-CH_2-CHO \xrightarrow{\Delta,\ -H_2O} CH_3-CH=CH-CHO$ (crotonaldehyde)
So the product formed in aldol condensation is a beta-hydroxy aldehyde or a beta-hydroxy ketone.