Which of the following compounds will undergo Cannizzaro reaction
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Benzaldehyde
In the Cannizzaro reaction, an aldehyde that has no α-hydrogen atom undergoes self oxidation and reduction (disproportionation) on heating with concentrated alkali. One molecule is reduced to the alcohol and another is oxidised to the salt of the carboxylic acid.
Benzaldehyde has no α-carbon at all (the CHO group is attached to the ring), so it gives the reaction:
\( \displaystyle \ce{2C6H5CHO + KOH} \xrightarrow[\Delta]{\text{conc.}} \ce{C6H5CH2OH + C6H5COOK} \)
An aldehyde that does have an α-hydrogen gives the aldol reaction with dilute alkali instead, because the alkali removes that hydrogen to form a carbanion.
Why the other options are incorrect
Option (2) Acetophenone — Incorrect. It is a ketone; the Cannizzaro reaction needs the H on the carbonyl carbon of an aldehyde, which moves as a hydride ion. Acetophenone also has α-hydrogens on its \( \ce{CH3} \) group and takes part in aldol condensation instead.
Option (3) Benzophenone — Incorrect. It has no α-hydrogen, but it is a ketone with no hydrogen on the carbonyl carbon, so it can neither give nor take a hydride in this way.
Option (4) Propionaldehyde — Incorrect. \( \ce{CH3CH2CHO} \) has α-hydrogens, so with dilute alkali it gives the aldol product:
\( \displaystyle \ce{2CH3CH2CHO} \xrightarrow{\text{dil. NaOH}} \ce{CH3CH2CH(OH)CH(CH3)CHO} \)
NCERT (2026-27 edition):
Other Reactions
