The compound which has most acidic hydrogen

Options

A. `CH_(3)CH_(2)NO_(2)`
B.
C.
D.

Answer

To determine which compound has the most acidic hydrogen, we need to analyze the compounds provided and their ability to stabilize the resulting conjugate base after deprotonation. Here’s a step-by-step breakdown of the solution:

### Step 1: Analyze Nitroethane
- **Structure**: Nitroethane has a nitro group (-NO2) attached to an ethyl group.
- **Acidic Hydrogen**: The hydrogen on the carbon adjacent to the nitro group is acidic.
- **Stabilization**: When this hydrogen is removed, the resulting anion can be stabilized by resonance with the nitro group. The negative charge can delocalize onto the electronegative oxygen atoms of the nitro group, making it a strong acid.

### Step 2: Analyze Phenol (Keto Form)
- **Structure**: The keto form of phenol has a hydroxyl group (-OH) attached to a benzene ring.
- **Acidic Hydrogen**: The hydrogen from the hydroxyl group is acidic.
- **Stabilization**: Upon losing this proton, the phenoxide ion is formed, which is stabilized by resonance. The negative charge can be delocalized over the aromatic ring, providing significant stabilization due to resonance and aromaticity.

### Step 3: Analyze Acetophenone
- **Structure**: Acetophenone has a carbonyl group (C=O) adjacent to a phenyl group.
- **Acidic Hydrogen**: The hydrogen on the carbon adjacent to the carbonyl group is acidic.
- **Stabilization**: The resulting enolate ion can be stabilized by resonance, but there are fewer resonance structures compared to phenoxide, making it less acidic.

### Step 4: Analyze Di-carbonyl Compound
- **Structure**: This compound has two carbonyl groups.
- **Acidic Hydrogen**: The hydrogen on the carbon between the two carbonyls is acidic.
- **Stabilization**: The negative charge can be delocalized onto both carbonyl groups, providing some stabilization, but it has fewer resonance structures compared to phenoxide.

### Step 5: Compare the Stabilization of Conjugate Bases
- **Nitroethane**: Strong stabilization due to the nitro group.
- **Phenol (Keto Form)**: Excellent stabilization due to resonance and aromaticity (3 resonance structures).
- **Acetophenone**: Moderate stabilization (2 resonance structures).
- **Di-carbonyl Compound**: Moderate stabilization (2 resonance structures).

### Conclusion
After comparing the stabilization of the conjugate bases formed from each compound, the **keto form of phenol** has the most acidic hydrogen due to its strong resonance stabilization and aromaticity.

### Final Answer
The compound which has the most acidic hydrogen is the **keto form of phenol**.

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