Which of the following can give highest yield in Friedel craft reaction?

Options

A.
B.
C.
D.

Answer

To determine which of the following can give the highest yield in a Friedel-Crafts reaction, we need to analyze the substituents on the benzene ring and their effects on the reaction. The Friedel-Crafts reaction can either be alkylation or acylation, and it requires an electrophile to react with the benzene ring.

### Step-by-Step Solution:

1. **Understanding Friedel-Crafts Reaction**:
- The Friedel-Crafts reaction involves the introduction of an alkyl or acyl group into an aromatic ring using a Lewis acid catalyst, typically AlCl3. The reaction can be represented as:
\[ \text{Benzene} + \text{Electrophile} \xrightarrow{\text{AlCl}_3} \text{Alkylated/Acylated Benzene} \]

2. **Identifying the Role of Substituents**:
- Substituents on the benzene ring can either activate or deactivate the ring towards electrophilic substitution. Electron-donating groups (EDGs) activate the ring and increase the yield of the reaction, while electron-withdrawing groups (EWGs) deactivate it.

3. **Evaluating the Given Options**:
- Let's consider the substituents mentioned in the question:
- **OH (Hydroxyl group)**: This group has a positive resonance effect (R effect) but also a negative inductive effect (I effect). However, it can form a complex with AlCl3, which can hinder the reaction.
- **Cl (Chlorine)**: Chlorine has a positive resonance effect but a stronger negative inductive effect. It can also deactivate the ring but is less effective than OH in terms of resonance.
- **NH2 (Amino group)**: This group has a strong positive resonance effect but can also form a complex with AlCl3, similar to OH, which can hinder the reaction.
- **C-O-NH2 (Amide group)**: This group is more of an electron-withdrawing group due to the presence of the carbonyl, which would deactivate the ring significantly.

4. **Conclusion**:
- Among the options, the groups OH and NH2 would form complexes with AlCl3, thus inhibiting the Friedel-Crafts reaction. Chlorine, while it has a negative inductive effect, does not form such a complex and can still participate in the reaction, albeit less effectively than an electron-donating group. Therefore, the best option for achieving the highest yield in a Friedel-Crafts reaction would be **Chlorobenzene**.

### Final Answer:
**Chlorobenzene** will give the highest yield in the Friedel-Crafts reaction.