Question

Which of the following alkyl halides is hydrolyzed by \( S_N 1 \) mechanism?

• A. \( \text{CH}_3\text{CH}_2\text{CX} \)
• B. \( \text{CH}_3\text{CH}_2\text{X} \)
• C. \( \text{CH}_3\text{CH}_2\text{CH}_2\text{X} \)
• D. \( \text{CH}_3\text{CH}_3\text{CX} \)

Hint:

\( S_N 1 \) reactions are more likely for compounds that form stable carbocations, typically secondary or tertiary carbon centers.

Answer 1

The Correct Option is A

Step 1: Understanding \( S_N 1 \) mechanism.
In the \( S_N 1 \) mechanism, the rate-determining step is the formation of a carbocation intermediate. Therefore, this mechanism is more likely to occur when a carbocation can be stabilized, such as in the case of tertiary carbocations or allylic/benzylic carbocations. Step 2: Analysis of options.
(A) \( \text{CH}_3\text{CH}_2\text{CX} \): Correct — The \( S_N 1 \) mechanism is favored for primary carbons with good leaving groups such as X. A carbocation can easily form when the leaving group departs.
(B) \( \text{CH}_3\text{CH}_2\text{X} \): This is incorrect; it would undergo \( S_N 2 \) instead of \( S_N 1 \).
(C) \( \text{CH}_3\text{CH}_2\text{CH}_2\text{X} \): This is incorrect because the alkyl group is primary, which favors the \( S_N 2 \) mechanism.
(D) \( \text{CH}_3\text{CH}_3\text{CX} \): This is incorrect because this molecule has a methyl group, which does not favor \( S_N 1 \).
Step 3: Conclusion.
The correct answer is (A) because it is the primary alkyl halide that can undergo the \( S_N 1 \) mechanism due to carbocation formation.