Which of the following substances does not give iodoform test ?
Correct answer: C. methyl alcohol
- A. acetaldehyde
- B. ethyl alcohol
- C. methyl alcohol
- D. acetone
Explanation
The iodoform test is positive for compounds containing the CH3CO group, and ethanol is oxidized under the test conditions to ethanal, which also gives the test. Acetaldehyde and acetone therefore produce yellow CHI3, but methanol has neither a methyl carbonyl group nor the ability to form ethanal. Students may choose acetaldehyde because it is an aldehyde, forgetting that acetaldehyde is the one aldehyde that gives the iodoform test.
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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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