Given: A compound reacts with I2 / NaOH. Does it give CHI3?
Reasoning Chain:
Step 1: Does the compound have a CH3CO- group directly?
- If YES → iodoform positive (methyl ketone or acetaldehyde)
- If NO → proceed to Step 2
Step 2: Can the compound be oxidized under I2/NaOH conditions to give a compound with CH3CO-?
- Primary alcohol CH3CH2OH (ethanol) → oxidized to CH3CHO → YES → iodoform positive
- Secondary alcohol CH3CHOH-R → oxidized to CH3CO-R → YES → iodoform positive (if R = H, it's isopropanol → acetone)
- Primary alcohol CH3CH2CH2OH (propan-1-ol) → oxidized to propanal (CH3CH2CHO) → no CH3CO- → NO
- If NO → proceed to Step 3
Step 3: Cannot be oxidized to CH3CO- compound.
- Result: NEGATIVE iodoform test
Application to Common Compounds
| Compound | CH3CO- group? | Oxidizable to CH3CO-? | Iodoform? |
|---|---|---|---|
| CH3CHO (acetaldehyde) | YES (itself) | — | Positive |
| CH3COCH3 (acetone) | YES (two) | — | Positive |
| CH3CH2OH (ethanol) | No | YES → CH3CHO | Positive |
| (CH3)2CHOH (isopropanol) | No | YES → CH3COCH3 | Positive |
| CH3OH (methanol) | No | → HCHO (no CH3CO-) | Negative |
| CH3CH2CH2OH (propan-1-ol) | No | → CH3CH2CHO (no CH3CO-) | Negative |
| CH3CH2COCH2CH3 (diethyl ketone) | No | No (already ketone, no CH3CO-) | Negative |
| C6H5COCH3 (acetophenone) | YES | — | Positive |
| C6H5CHO (benzaldehyde) | No | → C6H5COOH (no CH3CO-) | Negative |