Which of the following compound gives fastest `S_(N)2Ar` reaction?

Options

A.
B.
C.
D.

Explanation

To determine which compound gives the fastest \( S_N2Ar \) reaction, we need to understand the factors that influence the rate of nucleophilic aromatic substitution.

### Step-by-Step Solution:

1. **Understanding \( S_N2Ar \)**:
- \( S_N2Ar \) stands for Substitution Nucleophilic Aromatic reaction. This type of reaction occurs when a nucleophile attacks an aromatic compound, leading to the substitution of a leaving group (often a halogen).

2. **Role of Electron-Withdrawing Groups**:
- The rate of \( S_N2Ar \) reactions is significantly influenced by the presence of electron-withdrawing groups (EWGs) on the aromatic ring. These groups stabilize the negative charge that develops during the reaction mechanism.

3. **Identifying Electron-Withdrawing Groups**:
- Common electron-withdrawing groups include nitro groups (\(-NO_2\)), which exhibit a strong -M (mesomeric) effect and -I (inductive) effect. The presence of these groups decreases the electron density of the aromatic ring, making it more susceptible to nucleophilic attack.

4. **Analyzing the Given Compounds**:
- We need to evaluate the compounds provided in the question to identify which one has the strongest electron-withdrawing groups and thus the highest rate of \( S_N2Ar \).
- Look for the presence and position of electron-withdrawing groups relative to the leaving group (often a halogen).

5. **Comparing the Compounds**:
- **Compound 1**: No electron-withdrawing groups present.
- **Compound 2**: Has one EWG at ortho and one at para position.
- **Compound 3**: Contains two EWGs at ortho positions and one at the para position.
- **Compound 4**: Has one EWG at para position.

6. **Determining the Fastest Reaction**:
- The compound with the maximum number of electron-withdrawing groups in positions that can stabilize the negative charge during the reaction will undergo the \( S_N2Ar \) reaction the fastest.
- In this case, **Compound 3** has three nitro groups (two at ortho and one at para), which significantly decreases the electron density of the benzene ring, stabilizing the negative charge and facilitating a faster reaction.

7. **Conclusion**:
- Therefore, the compound that gives the fastest \( S_N2Ar \) reaction is **Compound 3**.

### Final Answer:
**Compound 3** gives the fastest \( S_N2Ar \) reaction.

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