The aldol reaction is a carbonyl condensation reaction between two carbonyl partners and involves a combination of nucleophilic addition and α-substitution steps. One partner is converted into an enolate ion nucleophile and adds to the electrophilic carbonyl group of the second partner. In the classic aldol reaction, the carbonyl partners are aldehydes or ketones, although aldehydes are more reactive. The product is a β-hydroxy carbonyl compound. In the mixed aldol reaction, the best results are obtained when one of the partners does not have an α-hydrogen. It cannot form an enolate anion and can therefore not undergo self-reaction. The enolizable aldehyde is added slowly to a basic solution of the first aldehyde so that the mixed product is preferentially formed. Under reaction conditions slightly more vigorous than those employed for the aldol reaction, the β-hydroxyl group is eliminated in an E1cB dehydration to give an α,β-unsaturated carbonyl compound. Draw curved arrows to show the movement of electrons in this step of the mechanism.