Which compound is the most acidic of the following ?

Options

A. `C_6H_5COOH`
B. `ClCH_2COOH`
C. `CD_3COOH`
D. `CH_3CH_2COOH`

Answer

To determine which compound is the most acidic among the given options, we need to analyze the structure of each compound and the presence of electron-withdrawing groups. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
Assume we have three compounds to analyze:
1. Benzoic acid (C6H5COOH)
2. A chlorinated benzoic acid (C6H4ClCOOH)
3. Another carboxylic acid without any electron-withdrawing groups.

### Step 2: Understand Acidity in Carboxylic Acids
The acidity of carboxylic acids is influenced by the stability of the carboxylate ion (the conjugate base formed after deprotonation). The more stable the conjugate base, the stronger the acid.

### Step 3: Analyze Electron-Withdrawing Groups
- **Benzoic Acid**: This compound has no electron-withdrawing groups. Therefore, it has a moderate acidity.

- **Chlorinated Benzoic Acid**: The presence of chlorine (an electron-withdrawing group) at the alpha position increases the acidity. Chlorine pulls electron density away from the carboxyl group, stabilizing the negative charge on the conjugate base (carboxylate ion) after deprotonation. This makes the acid stronger.

- **Third Compound**: If this compound has no electron-withdrawing groups and possibly has electron-donating groups (like alkyl groups), it would be the least acidic. Electron-donating groups destabilize the conjugate base, making the acid weaker.

### Step 4: Compare the Acidity
Based on the above analysis:
- Benzoic acid has moderate acidity.
- Chlorinated benzoic acid has increased acidity due to the electron-withdrawing effect of chlorine.
- The third compound, lacking electron-withdrawing groups, is the least acidic.

### Conclusion
The compound with the highest acidity is the chlorinated benzoic acid due to the presence of chlorine, which enhances the stability of the conjugate base.

### Final Answer
The most acidic compound is the second compound (chlorinated benzoic acid).

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