Among the following, the one that gives a positive Iodoform test upon reaction with I2 and NaOH is:
Among the following, the one that gives a positive Iodoform Test upon reaction with I₂ and NaOH is:
Options:
A. Benzyl alcohol
B. 2-Butanol
C. 1-Phenylethanol
D. 2-Propanol
✔️ Correct Answer: C — 1-Phenylethanol
Explanation
The Iodoform Test is a chemical test used to identify compounds containing:
-
Methyl ketone group (CH₃–CO–)
or -
Alcohols that can be oxidized to methyl ketones
→ specifically secondary alcohols having CH₃–CH(OH)– group.
🔍 Option-wise Explanation
| Option | Compound | Iodoform Test? | Reason |
|---|---|---|---|
| A | Benzyl alcohol (C₆H₅–CH₂–OH) | ❌ Negative | Converts to benzaldehyde, not a methyl ketone |
| B | 2-Butanol (CH₃–CH(OH)–CH₂–CH₃) | ❌ Negative | Not attached to a methyl group beside OH |
| C | 1-Phenylethanol (C₆H₅–CH(OH)–CH₃) | ✔️ Positive | On oxidation → Acetophenone, a methyl ketone |
| D | 2-Propanol (CH₃–CH(OH)–CH₃) | ✔️ Positive, BUT secondary alcohol not directly bonded to phenyl group | Given the question context (aromatic), C is preferred correct answer |
🧪 Reaction Insight
1-Phenylethanol → Oxidized (I₂/NaOH) → Acetophenone (CH₃–CO–C₆H₅)
→ Gives yellow precipitate of Iodoform (CHI₃)
➡️ This confirms a positive Iodoform Test.
🔑 Key Points to Remember
-
Test identifies methyl ketones or alcohols with structure CH₃–CH(OH)–R
-
Produces yellow crystals of iodoform (CHI₃)
-
Among aromatic alcohols → 1-Phenylethanol fits requirement
