"Aldehydes and ketones having at least one -hydrogen undergo a reaction in the presence of dilute alkali as a catalyst to form β-hydroxy aldehydes (aldol) or -hydroxy ketones (ketol), respectively. This is known as Aldol reaction."
-hydrogen is necessary for aldol condensation reaction.
Chemical reaction
Aldol condensation of ethanol is as follows
The mechanism for aldol condensation of ethanol is as follows