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

Answer: (A)

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