Question

Which of the following alkyl halides is hydrolyzed most rapidly by the \(\text{SN}^2\) mechanism ?

• A. \(\text{CH}_3\text{-Br}\)
• B. \((\text{CH}_3)_3\text{C-Br}\)
• C. \(\text{CH}_3\text{-CH}_2\text{-Br}\)
• D. \((\text{CH}_3)_2\text{CH-Br}\)

Hint:

SN2 is fastest where the carbon is least crowded: methyl halide.

Answer 1

The Correct Option is A

Step 1: Mechanism:
One step, back-side attack, so steric crowding at the carbon matters most.

Step 2: Compare:
Number of alkyl groups on the carbon: methyl 0, ethyl 1, isopropyl 2, tert-butyl 3. More groups mean more crowding and a slower reaction.

Step 3: Answer:
Methyl bromide in option (A) reacts fastest.

Final Answer:
Methyl bromide is the fastest SN2 substrate. \[ \boxed{\text{(A) }\text{CH}_3\text{-Br}} \]