Which of the following isomeric hydrocarbon is most acidic ?

Options

A.
B.
C.
D.

Answer

To determine which isomeric hydrocarbon is the most acidic, we need to analyze the stability of the anions formed after the removal of a proton (H⁺) from each hydrocarbon. The more stable the anion, the more acidic the hydrocarbon.

### Step-by-Step Solution:

1. **Identify the Isomers**:
Let's denote the isomeric hydrocarbons as A, B, C, and D. We need to analyze the structure of each isomer.

2. **Remove H⁺ from Each Isomer**:
For each isomer, we will remove a hydrogen atom (H) to form an anion. The position from which we remove H should ideally allow for resonance stabilization of the resulting anion.

3. **Analyze Resonance Stabilization**:
- **Isomer A**: After removing H⁺, the resulting anion can delocalize its negative charge through resonance. Count the number of resonance structures possible.
- **Isomer B**: Similarly, remove H⁺ and analyze the resonance structures. Count how many ways the negative charge can be delocalized.
- **Isomer C**: Repeat the process of removing H⁺ and counting resonance structures.
- **Isomer D**: Finally, remove H⁺ and analyze the resonance structures.

4. **Count the Resonance Structures**:
- For **Isomer A**, there are 4 resonance structures.
- For **Isomer B**, there are 3 resonance structures.
- For **Isomer C**, there are 4 resonance structures.
- For **Isomer D**, there are only 2 resonance structures.

5. **Compare Stability of Anions**:
- The stability of the anion is directly related to the number of resonance structures. More resonance structures generally mean greater stability.
- Between Isomers A and C, both have 4 resonance structures, but we need to consider the structure of the anions formed. If one has a more favorable arrangement of double bonds (like in a benzene ring), it will be more stable.

6. **Determine the Most Acidic Hydrocarbon**:
- Based on the resonance analysis, Isomer A will be the most acidic because it has the most stable anion due to its resonance structures being more favorable.

### Conclusion:
The most acidic isomeric hydrocarbon among A, B, C, and D is **Isomer A**.