Which among the following compounds wil be most reactive for `S_(N^(1))` reaction ?

Options

A.
B.
C.
D.

Answer

To determine which compound is most reactive for an SN1 reaction, we need to analyze the stability of the carbocations formed during the reaction. The stability of the carbocation is crucial because the rate of the SN1 reaction depends on the formation of this intermediate.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question provides four compounds. We need to analyze each compound to see which one will form the most stable carbocation upon the departure of the leaving group (halogen).

2. **Understand SN1 Mechanism**: In an SN1 reaction, the reaction proceeds in two steps:
- The leaving group (halogen) departs, forming a carbocation.
- The nucleophile attacks the carbocation, leading to the formation of the product.

3. **Carbocation Stability**: The stability of carbocations is determined by the degree of substitution:
- Tertiary (3°) carbocations are the most stable.
- Secondary (2°) carbocations are less stable than tertiary but more stable than primary (1°).
- Primary (1°) carbocations are less stable than secondary.
- Methyl (0°) carbocations are the least stable.
- Resonance can further stabilize carbocations (e.g., allylic and benzylic carbocations).

4. **Analyze Each Compound**:
- **Compound 1**: Cyclohexyl chloride → Forms a secondary carbocation (2°).
- **Compound 2**: Allylic cyclohexyl chloride → Forms an allylic carbocation, which is stabilized by resonance.
- **Compound 3**: Chlorinated cyclohexane with a methyl group → Forms a tertiary carbocation (3°).
- **Compound 4**: Allylic cyclohexyl chloride with additional chlorine → Forms a tertiary allylic carbocation, which is also stabilized by resonance.

5. **Determine the Most Reactive Compound**:
- The most stable carbocation will lead to the most reactive compound in an SN1 reaction.
- Comparing the stability:
- Compound 4 has a tertiary allylic carbocation, which is very stable due to both the tertiary nature and resonance.
- Compound 3 has a tertiary carbocation but lacks resonance stabilization.
- Compound 2 has an allylic carbocation, which is stable but less so than the tertiary ones.
- Compound 1 has the least stable secondary carbocation.

6. **Conclusion**: The compound that will be most reactive for an SN1 reaction is **Compound 4**, which forms a tertiary allylic carbocation.

### Final Answer:
**The most reactive compound for an SN1 reaction is Compound 4.**