Question

Which reaction, intermediate is formed during the condensation reaction between acetaldehyde and formaldehyde?

• A. $:\stackrel{-}{C}{H}_{2}CHO$
• B. $\stackrel{+}{C}{H}_{2}CHO$
• C. $\stackrel{+}{C}{H}_{2}OH$
• D. $:\stackrel{-}{C}HCHO$

Answer 1

The correct option is A $:\stackrel{-}{C}{H}_{2}CHO$

The $\alpha$- hydrogen atoms of acetaldehyde due to $-E$ effect of $C=O$ group is slightly acidic in nature. During the crossed aldol condensation between formaldehyde and acetaldehyde, in the first step, $O^{-}$ ion (from the base added) abstracts one of these acidic $\alpha$-hydrogens to form carboanion or enolate ion which is stabilized by resonance.