Write cross aldol condensation.

Explanation

Cross-aldol codensation : Aldol condensation between two different aldehydes or ketones, at least one of which contains `alpha`-hydrogen , is called crossed aldol condensation. It is a useful synethetic tool only when one of the aldehyde or ketone does not contain `alpha`-hydrogen. This is because if both the aldehydes or ketones contain `alpha`-hydrogen it gives a mixture of four different products.
For example : condensation between formaldehyde and acetaldehde in the presence of dil NaOH (aq).
`underset("Formaldehyde Acetaldehyde")(H-underset(H)underset(|)overset(O)overset(||)(C)+CH_(3)CHO) overset("Dil.NaoH")rarr underset(beta-"Hydroxypropionaldehyde")(H-underset(H)underset(|)overset(OH)overset(|)(C)-CH_(2)-CHO)underset(-H_(2)O)overset(Delta)rarr underset("Acrolein")(CH_(2)=CH-CHO)`