Which of the following compounds will not undergo Friedel Craft's reaction with benzene ?

Options

A.
B.
C.
D.

Answer

To determine which compound will not undergo Friedel-Crafts reaction with benzene, we need to analyze the stability of the carbocation intermediates formed during the reaction. The Friedel-Crafts reaction typically involves the formation of a carbocation that can then react with benzene.

### Step-by-Step Solution:

1. **Understanding Friedel-Crafts Reaction**:
The Friedel-Crafts reaction involves the alkylation or acylation of benzene using an alkyl halide or acyl halide in the presence of a Lewis acid (like AlCl3). The Lewis acid helps in generating a more stable carbocation from the alkyl or acyl halide.

2. **Analyzing the First Option**:
- The first option is a compound with a double bond and a chlorine atom (let's denote it as R-CH=CH-Cl).
- When this compound reacts with AlCl3, the chlorine atom can leave, forming a carbocation at the sp2 carbon.
- However, this carbocation is less stable because it is a primary carbocation (or a less stable secondary carbocation), which is not favorable for Friedel-Crafts reactions.
- **Conclusion**: This compound will not undergo Friedel-Crafts reaction.

3. **Analyzing the Second Option**:
- The second option is a compound with a pi bond and a chlorine atom (R-CH2-CH=CH-Cl).
- Here, when it reacts with AlCl3, a more stable carbocation can be formed due to resonance stabilization (the positive charge can be delocalized).
- **Conclusion**: This compound can undergo Friedel-Crafts reaction.

4. **Analyzing the Third Option**:
- The third option is a compound with a carbonyl group (C=O) and a chlorine atom (R-C=O-Cl).
- Upon reaction with AlCl3, the chlorine can leave, forming a resonance-stabilized carbocation.
- **Conclusion**: This compound can undergo Friedel-Crafts reaction.

5. **Analyzing the Fourth Option**:
- The fourth option is similar to the third but may have a different structure (C=C-COCl).
- Again, the chlorine can leave, and the resulting carbocation can be stabilized by resonance.
- **Conclusion**: This compound can undergo Friedel-Crafts reaction.

### Final Answer:
The compound that will not undergo Friedel-Crafts reaction with benzene is **Option 1**.