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The compound shown undergoes the Cannizzaro reaction, not the aldol reaction, with concentrated NaOH. Why?

  1. AIt has no alpha hydrogen, so it cannot form an enolate.
  2. BIt has too many alpha hydrogens.
  3. CIt is a ketone, and ketones do not undergo aldol reactions.
  4. DIts carbonyl carbon is not electrophilic.

Answer: A

The compound shown is benzaldehyde. The carbon bonded to the CHO group is an aromatic ring carbon with no hydrogen, so the compound has no alpha hydrogen and cannot be deprotonated to an enolate. With no aldol pathway, a hydroxide adds to the aldehyde and hydride transfer (Cannizzaro) occurs instead.
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