Which of the following can be used in Friedel Crafts reaction when benzene used with `AlCl_(3)`

Options

A.
B. `CH_(2) = CH – Cl`
C. `CH_(3)CH_(2)Cl`
D. `CH_(2)= CH–CH_(2)–Cl`

Answer

To determine which compounds can be used in a Friedel-Crafts reaction with benzene and AlCl3, we need to analyze the stability of the carbocations formed during the reaction. The Friedel-Crafts reaction involves the generation of an electrophile, which is typically a carbocation, that can then react with benzene.

### Step-by-Step Solution:

1. **Understanding Friedel-Crafts Reaction**:
- The Friedel-Crafts reaction is an electrophilic aromatic substitution reaction where an alkyl or acyl group is introduced into an aromatic ring (like benzene) using an alkyl halide (like R-X) and a Lewis acid catalyst (like AlCl3).

2. **Formation of Electrophile**:
- When an alkyl halide (e.g., CH3Cl) reacts with AlCl3, it forms a complex. The AlCl3 coordinates with the halide, generating a carbocation (R+). For example:
- CH3Cl + AlCl3 → CH3+ + AlCl4−
- The carbocation (CH3+) is the electrophile that will react with benzene.

3. **Evaluating Stability of Carbocations**:
- The stability of the carbocation is crucial for the reaction to proceed. More stable carbocations are more likely to form and react with benzene.
- Carbocation stability order: Tertiary > Secondary > Primary > Methyl.

4. **Analyzing Options**:
- We need to evaluate the given options based on the stability of the carbocations they can form:
- **Option 1: CH3Cl** (Methyl carbocation, CH3+): Least stable.
- **Option 2: CH2=CHCl** (Vinyl carbocation, CH2=CH+): Less stable due to sp2 hybridization.
- **Option 3: CH3CH2Cl** (Ethyl carbocation, CH3CH2+): More stable due to being a primary carbocation.
- **Option 4: CH2=CH-CH2Cl** (Allylic carbocation, CH2=CH-CH2+): More stable due to resonance stabilization.

5. **Conclusion**:
- The compounds that can effectively participate in the Friedel-Crafts reaction with benzene and AlCl3 are those that generate stable carbocations. Therefore, options 3 (ethyl) and 4 (allylic) are suitable for the Friedel-Crafts reaction.

### Final Answer:
The compounds that can be used in Friedel-Crafts reaction with benzene and AlCl3 are:
- **Option 3: CH3CH2Cl (Ethyl chloride)**
- **Option 4: CH2=CH-CH2Cl (Allyl chloride)**