There is an overall 29-fold difference in reactivity of 1-chlorohexane,2-chlorohexane towards potassium iodide in acetone. Which one is the most reactive? Why?

Answer

To determine the most reactive compound between 1-chlorohexane and 2-chlorohexane towards potassium iodide (KI) in acetone, we can analyze the structures and the mechanisms involved in the reaction.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **1-Chlorohexane**: This compound has the chlorine atom attached to the first carbon of a six-carbon chain. Its structure is:
\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{Cl} \]
- **2-Chlorohexane**: This compound has the chlorine atom attached to the second carbon of the six-carbon chain. Its structure is:
\[ \text{CH}_3\text{CH}(\text{Cl})\text{CH}_2\text{CH}_2\text{CH}_3 \]

2. **Determine the Reaction Conditions**:
- The reaction is taking place in acetone, which is a polar aprotic solvent. In this environment, the reaction mechanism that is favored is the SN2 mechanism.

3. **Understand the SN2 Mechanism**:
- The SN2 mechanism involves a backside attack of the nucleophile (I⁻ from KI) on the carbon atom bonded to the leaving group (Cl). The rate of the SN2 reaction is inversely proportional to steric hindrance around the carbon atom bearing the leaving group.

4. **Assess Steric Hindrance**:
- **1-Chlorohexane**: This is a primary alkyl halide, which has minimal steric hindrance. The nucleophile can easily approach the carbon atom bonded to chlorine.
- **2-Chlorohexane**: This is a secondary alkyl halide, which has more steric hindrance due to the presence of additional alkyl groups around the carbon bonded to chlorine. This makes it more difficult for the nucleophile to attack.

5. **Compare Reactivity**:
- Since 1-chlorohexane has less steric hindrance, it will react more readily with iodide ions in the SN2 mechanism compared to 2-chlorohexane. The overall 29-fold difference in reactivity indicates that 1-chlorohexane is significantly more reactive.

6. **Conclusion**:
- Therefore, **1-chlorohexane** is the most reactive towards potassium iodide in acetone due to its primary nature and lower steric hindrance, which facilitates the SN2 reaction.