Question

Formal dehyde undergoes aldol condensation but acetaldehyde undergo aldol condensation reaction Explain? ?

Answer 1

For a carbonyl compound to undergo aldol condensation, the necessary condition is that it MUST possess atleast 1 "alpha-hydrogen" (an alpha-hydrogen is a hydrogen attached to an alpha-carbon, while an alpha carbon is the carbon attached DIRECTLY to the functional group)
since formaldehyde(i-e HCHO) has only 1 carbon which is the carbonyl carbon (i-e the functional group) and there is no alpha-carbon present and hence no alpha-hydrogen, so formaldehyde doesn't undergo aldol condensation.
e.g Acetaldehyde can undergo aldol