Q. In a SN2 substitution reaction of the type R–Br + Cl⁻ —(DMF)→ R–Cl + Br⁻ Which one of the following has the highest relative rate?
A) CH₃CH₂Br
B) CH₃–CH₂–CH₂Br
C) (CH₃)₂CH–CH₂Br
D) (CH₃)₃C–CH₂Br
Explanation
[Solution from source] SN2 needs backside attack at the carbon bearing Br, so it slows as branching near that carbon increases steric hindrance. Ethyl bromide is the least hindered, so it reacts fastest. The neopentyl-type (CH₃)₃C–CH₂Br, though primary, is extremely hindered and reacts slowest. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.