Which one of the following compounds is most acidic

Options

A.
B.
C.
D. `Cl-CH_(2)-CH_(2)-OH`

Answer

To determine which compound is the most acidic among the given options, we need to analyze the stability of their conjugate bases. The more stable the conjugate base, the stronger the acid. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
First, we need to identify the compounds given in the question. Let's denote them as A, B, C, and D.

### Step 2: Understand Acidity and Conjugate Bases
Acidity is related to the stability of the conjugate base formed after the acid donates a proton (H⁺). A strong acid will have a stable conjugate base, which is often less basic.

### Step 3: Analyze the Conjugate Bases
For each compound, we will draw the conjugate base formed after deprotonation and analyze the stability based on the following factors:
- **Resonance:** Delocalization of the negative charge can stabilize the conjugate base.
- **Electronegative Atoms:** Presence of electronegative atoms can stabilize the negative charge.
- **Inductive Effects:** Electron-withdrawing groups can stabilize the negative charge, while electron-donating groups can destabilize it.

### Step 4: Evaluate Each Compound
- **Compound A:** The conjugate base does not have resonance stabilization and lacks any electron-withdrawing groups, making it less stable.
- **Compound B:** The conjugate base has some stability, but it lacks significant resonance or electron-withdrawing groups.
- **Compound C:** The conjugate base benefits from resonance stabilization due to the benzene ring and the -NO2 group, which has a -M (minus mesomeric) effect that helps to delocalize the negative charge. This makes it the most stable conjugate base.
- **Compound D:** The conjugate base is destabilized by the +M (plus mesomeric) effect of the -CH3 group, which increases electron density and destabilizes the negative charge.

### Step 5: Conclusion
Based on the analysis, Compound C has the most stable conjugate base due to resonance and the presence of an electron-withdrawing group. Therefore, Compound C is the most acidic.

### Final Answer
The most acidic compound is **C**.

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