Question

If a mixture of formaldehyde and acetaldehyde is subjected to aldol condensation, predict the products formed and draw their structures.

Answer 1

Since formaldehyde, 

does not have α-hydrogen atom it will not undergo self aldol condensation. 

Since acetaldehyde 

 has a-hydrogen atom, it will undergo self aldol condensation.

Formaldehyde and acetaldehyde undergo cross aldol condensation.

Hence two aldol condensation products will be obtained.