Which of the following is most reactive toward SNAr :

Options

A.
B.
C.
D.

Answer

To determine which compound is most reactive toward nucleophilic aromatic substitution (SNAr), we need to analyze the effects of substituents on the aromatic ring. The key factors influencing the reactivity in SNAr reactions are the presence and nature of substituents, particularly electron-withdrawing groups (EWGs) and their positions relative to the leaving group.

### Step-by-Step Solution:

1. **Understand the SNAr Mechanism**:
- Nucleophilic aromatic substitution (SNAr) occurs when a nucleophile attacks an aromatic ring that has a good leaving group (like a halide) and is activated by electron-withdrawing groups (EWGs).
- The nucleophile typically attacks the carbon atom that is bonded to the leaving group, especially if that carbon has a partial positive charge due to the influence of EWGs.

2. **Identify the Electron-Withdrawing Groups**:
- Electron-withdrawing groups such as nitro (NO2) groups increase the positive character of the carbon atom attached to the leaving group, making it more susceptible to nucleophilic attack.
- The more NO2 groups present on the aromatic ring, the greater the positive charge on the carbon, enhancing the reactivity.

3. **Analyze the Given Compounds**:
- Look at the compounds provided in the question (not specified here, but let's assume there are four options).
- Count the number of NO2 groups or other EWGs in each compound.

4. **Determine the Most Reactive Compound**:
- The compound with the highest number of electron-withdrawing groups (especially NO2) will have the most positive charge on the carbon atom bonded to the leaving group.
- This compound will be the most reactive toward nucleophilic aromatic substitution.

5. **Conclusion**:
- Based on the analysis, select the compound with the most NO2 groups as the answer. This compound will facilitate the fastest nucleophilic attack due to the increased positive charge on the carbon atom.

### Final Answer:
- The compound with the most electron-withdrawing groups (specifically, the one with the highest number of NO2 groups) is the most reactive toward SNAr. Therefore, the answer is **option 4** (assuming it has the most NO2 groups).