Which is most acidic ?

Options

A. `CF_3 COOH `
B. `C CI_3 COOH `
C. `CBr_3 COOH `
D. `CH_3 COOH `

Answer

To determine which compound is the most acidic among the given options, we need to analyze the stability of the conjugate base formed after the acid donates a proton (H+). The stability of the conjugate base is influenced by the electronegativity of the substituents attached to the carbon atom adjacent to the carboxylic group.

### Step-by-Step Solution:

1. **Identify the Compounds**: Let's assume the options are:
- A: CF3COOH
- B: CCl3COOH
- C: CBr3COOH
- D: C3H7COOH

2. **Understanding Acidity**: Acidity is determined by how well a compound can donate a proton (H+). When the compound donates H+, it forms a conjugate base (A-). The stability of this conjugate base is crucial in determining the strength of the acid.

3. **Formation of Conjugate Bases**:
- For A: CF3COO- (conjugate base)
- For B: CCl3COO- (conjugate base)
- For C: CBr3COO- (conjugate base)
- For D: C3H7COO- (conjugate base)

4. **Evaluate the Stability of Conjugate Bases**:
- The stability of the conjugate base is influenced by the inductive effect of the substituents (CF3, CCl3, CBr3, and C3H7).
- **CF3** is a strong electron-withdrawing group due to the high electronegativity of fluorine, which stabilizes the negative charge on the conjugate base.
- **CCl3** is less effective than CF3 but still withdraws electrons.
- **CBr3** is even less effective than CCl3.
- **C3H7** (alkyl group) is an electron-donating group, which destabilizes the negative charge.

5. **Compare the Effects**:
- CF3 > CCl3 > CBr3 > C3H7 in terms of electron-withdrawing ability.
- Therefore, CF3COO- is the most stable conjugate base due to the strong inductive effect of three fluorine atoms.

6. **Conclusion**: Since CF3COOH has the most stable conjugate base, it is the most acidic among the options provided.

### Final Answer:
The most acidic compound is **A: CF3COOH**.