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Which of the following compounds will NOT give a positive iodoform test?

1. CH3-CO-CH3
2. CH3-CO-Cl
3. CH3-CO-NH2
4. CH3-COOH

Correct answer: CH3-COOH

Solution

The iodoform test is positive when I2/NaOH can produce CHI3 (iodoform) from a compound. Any compound with the CH3CO- group (or that is oxidised to it) gives a positive test. Acetone (CH3COCH3), acetyl chloride (CH3COCl), and acetamide (CH3CONH2) all contain CH3CO- and give CHI3. Acetic acid (CH3COOH) does not undergo iodoform reaction because the -COOH group resists the necessary alpha-halogenation/hydrolysis sequence under basic iodine conditions.

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