Iodoform test is used to identify compounds containing:$$\boxed{CH_3CO-}$$

or compounds that can be oxidised to a methyl ketone.

1. Reagent

$$\boxed{I_2 + NaOH}$$

Positive test: formation of a yellow precipitate of iodoform$$\boxed{CHI_3 = \text{yellow precipitate}}$$

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2. Main compounds giving the test

A. Methyl ketones

General structure:$$\boxed{R-CO-CH_3}$$

Example:$$CH_3COCH_3 \xrightarrow{I_2/NaOH} CHI_3\downarrow$$

So acetone gives iodoform test.

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B. Ethanol

Ethanol is oxidised to acetaldehyde, which gives the test:$$CH_3CH_2OH \rightarrow CH_3CHO \rightarrow CHI_3$$

Therefore:$$\boxed{CH_3CH_2OH \text{ gives iodoform test}}$$

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C. Secondary alcohols of type

$$\boxed{CH_3-CH(OH)-R}$$

These are oxidised to:$$CH_3-CO-R$$

which is a methyl ketone.

Example:$$CH_3CH(OH)CH_3$$

Propan-2-ol → positive.

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3. Important examples

Compound	Iodoform test
$CH_3COCH_3$	✅
$CH_3COCH_2CH_3$	✅
$CH_3CHO$	✅
$CH_3CH_2OH$	✅
$CH_3CH(OH)CH_3$	✅
$CH_3CH(OH)C_2H_5$	✅
$CH_3CH_2CH_2OH$	❌
$CH_3COOH$	❌

JEE/NEET shortcut

Look for:$$\boxed{CH_3CO-}$$

OR$$\boxed{CH_3CH(OH)-}$$

If either is present → Iodoform test is generally positive.

Special exception

Acetaldehyde (CH3CHO) gives the iodoform test even though it is not a methyl ketone.$$\boxed{CH_3CHO \rightarrow CHI_3\downarrow}$$