Benzyl amine reacts with alkyl halide as shown in the following reaction:
`C_6H_5-CH_2-NH_2 + R-X rarr C_6H_5-CH_2-NH-R`
which of the following alkyl halide is best suited for this reaction through `SN^1` mechanism?

Options

A. `CH_3-Br`
B. `C_6H_5-Br`
C. `C_6H_5-CH_2-Br`
D. `C_2H_5-Br`

Answer

To determine which alkyl halide is best suited for the reaction of benzyl amine with alkyl halides through an SN1 mechanism, we need to analyze the stability of the carbocations that would be formed during the reaction.

### Step-by-Step Solution:

1. **Understand the Reaction**: Benzyl amine (C6H5-CH2-NH2) reacts with an alkyl halide (R-X) to form a secondary amine (C6H5-CH2-NH-R). The reaction involves the formation of a carbocation intermediate.

2. **Identify the Mechanism**: The SN1 mechanism is a unimolecular nucleophilic substitution reaction. It involves two steps:
- Formation of a carbocation from the alkyl halide.
- Nucleophilic attack by the amine on the carbocation.

3. **Carbocation Stability**: The stability of the carbocation is crucial for the SN1 mechanism. More stable carbocations will favor the reaction. The stability order of carbocations is:
- Tertiary > Secondary > Primary > Methyl
- Additionally, resonance stabilization significantly enhances carbocation stability.

4. **Evaluate Possible Carbocations**:
- **Methyl Carbocation (CH3+)**: No stability, as it has no substituents to stabilize the positive charge.
- **Primary Carbocation (R-CH2+)**: Slightly stable due to one alkyl group.
- **Secondary Carbocation (R2CH+)**: More stable due to two alkyl groups.
- **Benzylic Carbocation (C6H5-CH2+)**: Highly stable due to resonance with the aromatic ring.
- **Phenolic Carbocation (C6H5+)**: Less stable than benzylic due to lack of resonance stabilization.

5. **Conclusion**: Among the possible carbocations, the benzylic carbocation (C6H5-CH2+) is the most stable due to resonance stabilization from the adjacent aromatic ring. Therefore, an alkyl halide that can form a benzylic carbocation would be best suited for the SN1 reaction with benzyl amine.

6. **Final Answer**: The best-suited alkyl halide for this reaction through the SN1 mechanism is the one that can form a benzylic carbocation.