Question

Which one of the following halogen compounds is least reactive towards hydrolysis by S$_N$1 mechanism?

• A. Tertiary butyl chloride
• B. Isopropyl chloride
• C. Allyl chloride
• D. Ethyl chloride

Hint:

S$_N$1 reactivity follows carbocation stability: 3°>2°>1°. Resonance (e.g., allyl, benzyl) boosts reactivity in primary halides.

Answer 1

The Correct Option is D

To solve the problem, we need to determine which halogen compound is least reactive towards hydrolysis by the SN1 mechanism. The reactivity towards SN1 is influenced by the stability of the carbocation formed during the mechanism. The more stable the carbocation, the more reactive the compound is.

1. Understanding the Concepts:

- SN1 Mechanism: The SN1 reaction involves the formation of a carbocation intermediate. The rate of the reaction depends on the stability of this intermediate.

- Carbocation Stability: Tertiary carbocations are the most stable, followed by secondary, and then primary carbocations. The more stable the carbocation, the more reactive the compound is towards hydrolysis in the SN1 mechanism.

2. Given Values:

The given options are:

• 1. Tertiary butyl chloride
• 2. Isopropyl chloride
• 3. Allyl chloride
• 4. Ethyl chloride

3. Analyzing the Options:

1. Tertiary butyl chloride: Forms a very stable tertiary carbocation, so it's highly reactive.

2. Isopropyl chloride: Forms a secondary carbocation, which is less stable than the tertiary carbocation.

3. Allyl chloride: Forms a resonance-stabilized carbocation, making it highly reactive despite being primary.

4. Ethyl chloride: Forms a primary carbocation, which is the least stable and thus the least reactive in an SN1 mechanism.

Final Answer:

The least reactive compound towards hydrolysis by the SN1 mechanism is Ethyl chloride (Option 4).