Which one of the following compounds gives a positive iodoform test?

Options

A. Pentanal
B. 1-phenyl ethanol
C. 2-phenyl ethanol
D. 3-pentanol

Answer

To determine which compound gives a positive iodoform test, we need to follow these steps:

### Step 1: Understand the Iodoform Test
The iodoform test is a chemical reaction used to identify the presence of a methyl ketone (or a compound that can be oxidized to a methyl ketone) in a compound. The key requirement for a positive iodoform test is the presence of an active methyl group (–C(=O)CH3) adjacent to a carbonyl group (C=O).

### Step 2: Identify the Compounds
Let’s analyze the given compounds to see if they contain an active methyl group:
- **Option A: Phenyl ethanol (C6H5CH2OH)**
- **Option B: Acetophenone (C6H5C(=O)CH3)**
- **Option C: Butan-2-ol (C4H10O)**
- **Option D: Ethyl alcohol (C2H5OH)**

### Step 3: Analyze Each Compound
1. **Phenyl ethanol (C6H5CH2OH)**:
- Structure: C6H5-CH2-OH
- No carbonyl group present, hence cannot form a methyl ketone. **Does not give a positive iodoform test.**

2. **Acetophenone (C6H5C(=O)CH3)**:
- Structure: C6H5-C(=O)-CH3
- Contains a carbonyl group (C=O) and an adjacent methyl group (–CH3). This compound can be oxidized to form iodoform (CHI3). **Gives a positive iodoform test.**

3. **Butan-2-ol (C4H10O)**:
- Structure: CH3-CH(OH)-CH2-CH3
- This compound can also be oxidized to form a methyl ketone (C=O adjacent to –CH3). **Gives a positive iodoform test.**

4. **Ethyl alcohol (C2H5OH)**:
- Structure: C2H5-OH
- No carbonyl group present, hence cannot form a methyl ketone. **Does not give a positive iodoform test.**

### Step 4: Conclusion
From the analysis, we see that both **Acetophenone (Option B)** and **Butan-2-ol (Option C)** can give a positive iodoform test. However, since the question asks for "which one," the most straightforward answer is **Acetophenone (Option B)** as it is a classic example of a compound that gives a positive iodoform test.

### Final Answer:
**Acetophenone (Option B)** gives a positive iodoform test.

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