In the iodoform test, a yellow precipitate is given by
Correct answer: C. ethanol and other alcohols containing the CH3CH(OH) group
- A. any primary alcohol
- B. methanol
- C. ethanol and other alcohols containing the CH3CH(OH) group
- D. all tertiary alcohols
Explanation
The test needs a methyl group attached to the carbon bearing the hydroxyl, so ethanol and propan-2-ol respond while methanol and propan-1-ol do not. Iodine in alkali oxidises and then cleaves the molecule, leaving the yellow crystalline triiodomethane. Methyl ketones give the same positive result for the same structural reason.
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About Alcohols
Alcohols contain a hydroxyl group attached to a saturated carbon atom and are classified as primary, secondary or tertiary. Their nomenclature, hydrogen bonding, acidity, oxidation, dehydration, reaction with sodium and conversion to haloalkanes are covered, along with the distinction between alcohols and phenols, where the hydroxyl group is attached directly to an aromatic ring.
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