Which of the following will not form iodoform with `I_2// overset(-)(O)H`?

Options

A. Ethanol
B. Ethanal
C. Isopropyl alcohol
D. Benzyl alcohol

Answer

To determine which of the given compounds will not form iodoform with `I2` in the presence of `OH-`, we need to analyze the structures of each compound and see if they contain the necessary functional groups that can undergo the iodoform reaction.

### Step-by-Step Solution:

1. **Understanding the Iodoform Reaction**:
The iodoform test is positive for compounds that have a methyl ketone group (RCOCH3) or a secondary alcohol that can be oxidized to a methyl ketone. The presence of the group -C(=O)CH3 is essential for the formation of iodoform (CHI3).

2. **Analyzing Each Option**:
- **Option A: Ethanol (C2H5OH)**:
- Structure: CH3-CH2-OH
- Ethanol does not have a methyl ketone group. However, it can be oxidized to acetaldehyde (which has the structure CH3CHO), and acetaldehyde can form iodoform. Thus, ethanol can give a positive iodoform test.

- **Option B: Acetaldehyde (CH3CHO)**:
- Structure: CH3-CHO
- Acetaldehyde has the methyl group adjacent to the carbonyl group (C=O). Therefore, it can directly form iodoform. This will also give a positive iodoform test.

- **Option C: Isopropyl Alcohol (CH3CHOHCH3)**:
- Structure: (CH3)2CHOH
- Isopropyl alcohol can be oxidized to acetone (CH3COCH3), which has the methyl ketone structure. Hence, it will also give a positive iodoform test.

- **Option D: Benzyl Alcohol (C6H5CH2OH)**:
- Structure: C6H5-CH2-OH
- Benzyl alcohol does not have a methyl ketone group, nor can it be oxidized to form one. Therefore, it will not give a positive iodoform test.

3. **Conclusion**:
Based on the analysis, the compound that will not form iodoform with `I2` and `OH-` is **Benzyl Alcohol** (Option D).

### Final Answer:
**Option D: Benzyl Alcohol**