Which of the following is a false statement?

Question

BlackTom AI · Accepted Answer

Sodium borohydride (NaBH4) is a mild hydride donor that reduces aldehydes and ketones to alcohols but generally does not reduce amides to amines. Amides are stabilized by strong resonance between the nitrogen lone pair and the C=O, making the carbonyl carbon far less electrophilic than in aldehydes/ketones. Because NaBH4 is a relatively weak hydride source, it cannot efficiently attack this less electrophilic amide carbonyl. Stronger reducing agents such as lithium aluminum hydride (LiAlH4) are required to supply the more reactive hydride and fully reduce amides to amines.

Step-by-step reasoning through each option:
1) Option a: “The full reduction of a ketone gives an alkane.” Interpret “full reduction” as removal of the carbonyl oxygen (reduction beyond the alcohol stage). This is achievable (e.g., Wolff–Kishner or Clemmensen reductions convert a ketone to an alkane), so the statement is effectively true in the usual organic-chemistry sense.
2) Option b: “Sodium borohydride reduces amides to amines.” Mechanistically, NaBH4 transfers hydride to electrophilic carbonyl carbons; amide carbonyls are deactivated by N → C=O resonance, so NaBH4 cannot generally perform this transformation. LiAlH4 is the standard reagent for reducing amides to amines. Therefore option b is false.
3) Option c: “Acid catalysis makes a carbonyl compound more electrophilic.” Protonation of the carbonyl oxygen increases the positive character on the carbonyl carbon, enhancing its susceptibility to nucleophilic attack — this is a correct statement.
4) Option d: “The ozonolysis of an alkene gives two carbonyl compounds.” Ozonolysis cleaves an alkene’s C=C to give two carbonyl-containing fragments (aldehydes or ketones, depending on substitution and workup), so this is true.

Why b is the correct false choice: NaBH4 is too mild to reduce amides because of resonance-stabilized, less-electrophilic amide carbonyls; the typical reagent for that conversion is LiAlH4. Therefore the false statement is option b, matching the provided answer.

Which of the following is a false statement?单项选择题

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