Acetaldehyde cannot show
Correct answer: B. Lucas test
- A. Iodoform test
- B. Lucas test
- C. Benedict's test
- D. Tollen's test
Explanation
Acetaldehyde gives the iodoform test because it contains the CH3CO- equivalent, and it gives Benedict's and Tollens' tests because it is readily oxidised. Lucas reagent tests alcohols through formation of an alkyl chloride, and acetaldehyde has no hydroxyl group, so it cannot show this test. Students may choose Benedict's test if they forget that aldehydes are reducing substances.
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About Reactivity of Aldehydes and Ketones
The polar carbonyl group makes aldehydes and ketones undergo nucleophilic addition, reduction and condensation reactions. Aldehydes are generally more reactive and oxidise readily to carboxylic acids, whereas ketones resist mild oxidation; reactions with hydrogen cyanide, sodium bisulfite and 2,4-DNP help identify their behaviour.
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