Which of the following compounds will not undergo Friedel`-` Crafts reaction easily ?

Options

A.
B.
C.
D.

Answer

To determine which compound will not undergo Friedel-Crafts reaction easily, we first need to understand the mechanism and stability of the intermediates formed during the reaction. The Friedel-Crafts reaction can be either alkylation or acylation, and it involves the formation of carbocations.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have several compounds to analyze. Let's denote them as:
- Option A: Vinyl chloride (C2H3Cl)
- Option B: Allylic chloride (C3H5Cl)
- Option C: Carbonyl compound (e.g., CH3COCl)
- Option D: Another carbonyl compound (e.g., C6H5COCl)

2. **Understand Friedel-Crafts Mechanism**:
- Friedel-Crafts alkylation involves the formation of a carbocation from an alkyl halide in the presence of a Lewis acid (like AlCl3).
- Friedel-Crafts acylation involves the formation of an acylenium ion from an acyl halide in the presence of a Lewis acid.

3. **Analyze Stability of Carbocations**:
- **Vinyl Cation**: The vinyl cation (formed from vinyl chloride) is less stable because it is sp2 hybridized and has no resonance stabilization.
- **Allylic Cation**: The allylic cation (formed from allylic chloride) is more stable due to resonance stabilization.
- **Acylenium Ion**: The acylenium ion (from acyl halides) is stabilized by resonance and backbonding, making it stable.

4. **Evaluate Each Option**:
- **Option A (Vinyl Chloride)**: Forms a vinyl cation, which is unstable and does not favor the Friedel-Crafts reaction.
- **Option B (Allylic Chloride)**: Forms an allylic cation, which is stable and can undergo Friedel-Crafts reaction.
- **Option C (Carbonyl Compound)**: Forms a stable acylenium ion, which can undergo Friedel-Crafts acylation.
- **Option D (Another Carbonyl Compound)**: Similar to Option C, it forms a stable acylenium ion.

5. **Conclusion**:
Based on the stability of the carbocations formed, **Vinyl Chloride (Option A)** will not undergo the Friedel-Crafts reaction easily due to the instability of the vinyl cation.

### Final Answer:
**Vinyl chloride will not undergo Friedel-Crafts reaction easily.**