Which of the following compounds is most acidic ?

Options

A. `CH_(3)CO_(2)H`
B. `(CH_(3))_(2)CHCO_(2)H`
C. `CH_(3)CH_(2)CO_(2)H`
D. `C Cl_(3)CO_(2)H`

Explanation

To determine which of the given compounds is the most acidic, we need to analyze the stability of their conjugate bases. The acidic strength of a compound is directly proportional to the stability of its conjugate base; the more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's denote the four compounds as follows:
- Compound 1: CH3COOH (Acetic acid)
- Compound 2: CH3C(=O)OH (Acetaldehyde)
- Compound 3: CH3CH2C(=O)OH (Propanoic acid)
- Compound 4: CCl3COOH (Trichloroacetic acid)

2. **Write the Conjugate Bases**:
The conjugate bases of these acids can be represented as follows:
- Conjugate base of Compound 1: CH3COO⁻ (Acetate ion)
- Conjugate base of Compound 2: CH3C(=O)O⁻ (Acetate ion)
- Conjugate base of Compound 3: CH3CH2C(=O)O⁻ (Propionate ion)
- Conjugate base of Compound 4: CCl3COO⁻ (Trichloroacetate ion)

3. **Analyze Stability of Conjugate Bases**:
- **Compound 1 (Acetate ion)**: The negative charge is delocalized over the two oxygen atoms, providing some stability.
- **Compound 2 (Acetate ion)**: Similar to Compound 1, it has delocalization but lacks additional stabilizing factors.
- **Compound 3 (Propionate ion)**: The negative charge is also delocalized, but the presence of an additional alkyl group (ethyl) can increase electron density, making it less stable.
- **Compound 4 (Trichloroacetate ion)**: The presence of three electronegative chlorine atoms withdraws electron density from the conjugate base, stabilizing the negative charge significantly.

4. **Determine the Most Stable Conjugate Base**:
Among the conjugate bases, the trichloroacetate ion (from Compound 4) is the most stable due to the strong electron-withdrawing effect of the three chlorine atoms. This stabilization of the negative charge makes the conjugate base more stable than the others.

5. **Conclusion**:
Since the stability of the conjugate base is highest for Compound 4 (CCl3COOH), it is the most acidic among the given compounds.

### Final Answer:
The most acidic compound is **CCl3COOH (Trichloroacetic acid)**.

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