Which compound has least `e^(-)` density in benzene ring

Options

A.
B.
C.
D.

Answer

To determine which compound has the least electron density in the benzene ring, we need to analyze the effect of substituents on the benzene ring. The substituents can either donate or withdraw electron density through resonance or inductive effects.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have four compounds to analyze. Let's denote them as:
- Compound A: \( \text{C}_6\text{H}_5\text{OH} \) (Phenol)
- Compound B: \( \text{C}_6\text{H}_5\text{NH}_2 \) (Aniline)
- Compound C: \( \text{C}_6\text{H}_5\text{COOH} \) (Benzoic Acid)
- Compound D: \( \text{C}_6\text{H}_5\text{O}^- \) (Phenoxide ion)

2. **Analyze Electron-Donating and Electron-Withdrawing Effects**:
- **Compound A (Phenol)**: The hydroxyl group (-OH) is an electron-donating group through resonance (+M effect), which increases electron density in the benzene ring.
- **Compound B (Aniline)**: The amino group (-NH2) is also an electron-donating group through resonance (+M effect), which increases electron density in the benzene ring.
- **Compound C (Benzoic Acid)**: The carboxylic acid group (-COOH) is an electron-withdrawing group (-M effect), which decreases electron density in the benzene ring.
- **Compound D (Phenoxide ion)**: The phenoxide ion has a negative charge on oxygen, which significantly increases electron density in the benzene ring due to the resonance stabilization of the negative charge.

3. **Determine the Compound with the Least Electron Density**:
- From the analysis, we see that both phenol and aniline increase electron density, while benzoic acid decreases it. The phenoxide ion has the highest electron density due to the negative charge.
- Therefore, **Compound C (Benzoic Acid)** has the least electron density in the benzene ring due to the electron-withdrawing effect of the -COOH group.

### Conclusion:
The compound with the least electron density in the benzene ring is **Benzoic Acid (Compound C)**.