MCQ Detailed View

The Clemmensen reduction is an important name reaction in organic chemistry that involves the reduction of carbonyl compounds into hydrocarbons. It is carried out using zinc amalgam (Zn-Hg) and concentrated hydrochloric acid. The reaction is especially useful for ketones and aldehydes that are stable under strongly acidic conditions.

Acetone, with the formula CH₃–CO–CH₃, is the simplest aliphatic ketone. In the Clemmensen reduction, the carbonyl group (C=O) of acetone is completely reduced to a methylene group (–CH₂–). This transforms acetone into propane (CH₃–CH₂–CH₃), a saturated hydrocarbon. The overall reaction can be summarized as:

CH₃–CO–CH₃ →(Zn-Hg/HCl)→ CH₃–CH₂–CH₃

This reaction is valuable because it removes the oxygen atom entirely and replaces the carbonyl function with hydrogen atoms, converting a polar functional group into a nonpolar hydrocarbon chain.

Looking at the options:

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  Ethanol is a two-carbon alcohol, which cannot result from reducing a three-carbon ketone like acetone.

  
  


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  Ethanal (acetaldehyde) is a two-carbon aldehyde, not related to the complete reduction of acetone.

  
  


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  Propanol is a three-carbon alcohol that may be obtained by partial reduction of acetone using different reagents such as NaBH₄ or LiAlH₄, but not by Clemmensen reduction.

  
  


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  Propane is the correct product because Clemmensen reduction eliminates the oxygen atom and saturates the molecule fully.

  
  

The Clemmensen reduction is often contrasted with the Wolff–Kishner reduction, which achieves the same transformation under strongly basic conditions using hydrazine and a base. Both reactions convert carbonyl groups into methylene groups, but the choice between them depends on whether the substrate is stable in acidic or basic medium.

Thus, acetone under Clemmensen reduction conditions yields propane, a hydrocarbon without any oxygen functionality.