Iodoform test will not be positive with:
Correct answer: A. A
- A. A
- B. B
- C. C
- D. D
Explanation
Iodoform test is a test for the presence of a methyl ketone or a compound containing methyl group is adjacent to the functional group. In this test, the compound is treated with iodine in the presence of a mild base such as sodium hydroxide (NaOH), and the formation of a yellow precipitate of iodoform (CHI3) indicates the presence of a methyl ketone or a compound containing CH3 adjacent to functional group.Out of the given options, only option A (H₂C-CH₂-CO-CH₂-CH3) does not have a methyl group adjacent to the carbonyl group. Therefore, iodoform test will not be positive for option A. Options B (H3C--CH2-CO-CH3), C (C2H5OH), and D (H3C-CO-H) have a methyl group adjacent to the functional group, and hence, will give a positive iodoform test.
This question appeared on the UHS MDCAT 2012 paper, which you can sit online with every answer explained.
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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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