MHT CET · Chemistry · Aldehydes and Ketones

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

A \(: \overline{\mathrm{CH}}_{2} \mathrm{CHO}\)
B \(\mathrm{C}_{2}^{+} \mathrm{CHO}\)
C \(\stackrel{+}{\mathrm{CH}_{2} \mathrm{OH}}\)
D \(: \overline{\mathrm{C}} \mathrm{HCHO}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(: \overline{\mathrm{CH}}_{2} \mathrm{CHO}\)

Step-by-step Solution

Detailed explanation

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

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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