Which of the following will undergo Friedel-Crafts alkylation reaction ?

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds will undergo Friedel-Crafts alkylation, we need to analyze the substituents on the benzene ring in each option. Friedel-Crafts alkylation is an electrophilic substitution reaction that requires the presence of an electron-donating group or a group that does not significantly withdraw electrons from the aromatic ring.

### Step-by-Step Solution:

1. **Understand Friedel-Crafts Alkylation**:
- Friedel-Crafts alkylation involves the reaction of an alkyl halide with an aromatic compound in the presence of a Lewis acid catalyst (like AlCl3) to form an alkyl-substituted aromatic compound.

2. **Identify the Role of Substituents**:
- Substituents on the benzene ring can be classified as electron-donating or electron-withdrawing. Electron-donating groups increase the electron density of the ring, making it more reactive towards electrophiles, while electron-withdrawing groups decrease the electron density, making it less reactive.

3. **Analyze Each Option**:
- **Option A**: Contains a methyl group (–CH3) as a substituent. The methyl group is an electron-donating group, which increases the electron density of the benzene ring. Therefore, Friedel-Crafts alkylation can occur.

- **Option B**: Contains a chlorine atom (–Cl) as a substituent. Chlorine is an electron-withdrawing group but also has lone pairs that can donate electron density to the ortho and para positions. Thus, Friedel-Crafts alkylation can occur here as well.

- **Option C**: Contains a carboxylic acid group (–COOH) as a substituent. The carboxylic acid is a strong electron-withdrawing group, which deactivates the benzene ring towards electrophilic substitution. Therefore, Friedel-Crafts alkylation cannot occur.

- **Option D**: Contains a bromine atom (–Br) as a substituent. Similar to chlorine, bromine is an electron-withdrawing group but can also donate electron density through its lone pairs. Thus, Friedel-Crafts alkylation can occur here as well.

4. **Conclusion**:
- The compounds that can undergo Friedel-Crafts alkylation are those in **Options A, B, and D**. Option C cannot undergo this reaction due to the presence of a strong electron-withdrawing group.

### Final Answer:
- **Options A, B, and D will undergo Friedel-Crafts alkylation.**

---