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Difficulty: HardAlkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

Compound WW is a four-carbon carbonyl compound that yields a negative result when tested with ammoniacal silver nitrate solution. Complete reduction of compound WW using lithium aluminium hydride (LiAlH4\text{LiAlH}_4) produces an alcohol, compound ZZ. What is the IUPAC name of compound ZZ?

Answer: butan-2-ol / 2-butanol / Butan-2-ol / 2-Butanol

Answer

The IUPAC name of compound ZZ is butan-2-ol.
Compound WW does not react with Tollen's reagent (ammoniacal silver nitrate), which confirms it is an alkanone rather than an alkanal. The only four-carbon alkanone is butan-2-one. Reducing butan-2-one with LiAlH4\text{LiAlH}_4 yields the secondary alcohol butan-2-ol.

Step-by-Step Solution

1
Determine the functional group of compound WW based on the distinction test.
Compound WW is an alkanone (ketone).
Alkanals (aldehydes) reduce ammoniacal silver nitrate (Tollen's reagent) to silver metal (silver mirror), whereas alkanones (ketones) give a negative result.
2
Identify the specific structure and IUPAC name of compound WW.
Compound WW is butan-2-one (CH3COCH2CH3\text{CH}_3\text{COCH}_2\text{CH}_3).
Since compound WW is a four-carbon alkanone, its only structural isomer is butan-2-one.
3
Determine the product of the reduction reaction.
Compound ZZ is a secondary alcohol, butan-2-ol (CH3CH(OH)CH2CH3\text{CH}_3\text{CH(OH)CH}_2\text{CH}_3).
Reduction of alkanones with LiAlH4\text{LiAlH}_4 converts the carbonyl group (C=O\text{C=O}) into a secondary alcohol group (CH-OH\text{CH-OH}).

Key Concept

Reduction of alkanones to secondary alcohols and distinction between alkanals and alkanones using Tollen's reagent
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Topics

Alkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

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