Which of the following is least reactive in a nucleophilic substitution reaction?

Options

A. `(CH_(3))_(3)C-Cl`
B. `CH_(2)=CHCl`
C. `CH_(3)CH_(2)Cl`
D. `CH_(2)=CHCH_(2)Cl`

Answer

To determine which of the given organic compounds is least reactive in a nucleophilic substitution reaction, we need to analyze the reactivity of each compound based on the stability of their transition states. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
First, we need to identify the compounds provided in the question. Typically, these would include various types of halides, such as alkyl halides, allyl halides, benzyl halides, and aryl halides.

### Step 2: Understand Nucleophilic Substitution
Nucleophilic substitution reactions involve the replacement of a leaving group (usually a halide) by a nucleophile. The reactivity of the compound depends on the stability of the transition state formed during the reaction.

### Step 3: Analyze the Transition States
The stability of the transition state is crucial in determining the reactivity of the compound:
- **Alkyl Halides**: Generally have good reactivity due to the formation of a stable carbocation in the transition state.
- **Allyl Halides**: The transition state can be stabilized by resonance, making them more reactive than simple alkyl halides.
- **Benzyl Halides**: Similar to allyl halides, they benefit from resonance stabilization, making them quite reactive.
- **Aryl Halides**: The carbon atom bonded to the halogen is part of an aromatic system, which makes the transition state less stable due to the disruption of the aromaticity. Thus, aryl halides are the least reactive in nucleophilic substitution reactions.

### Step 4: Conclusion
Based on the analysis, the compound that is least reactive in a nucleophilic substitution reaction is the **aryl halide**.

### Summary of Reactivity
1. **Alkyl Halides**: More reactive
2. **Allyl Halides**: Reactive (due to resonance)
3. **Benzyl Halides**: Reactive (due to resonance)
4. **Aryl Halides**: Least reactive (due to instability of the transition state)

### Final Answer
The least reactive compound in a nucleophilic substitution reaction is the **aryl halide**.

---