Answer: CH3Br.
- A (CH3)3CBr
- B (CH3)2CHBr
- C CH3CH2Br
- D CH3Br
Correct answer: D. CH3Br
Explanation: SN2 rate: methyl > primary > secondary > tertiary. CH₃Br has essentially no steric hindrance at the reaction centre; it reacts fastest in SN2.
SN2 proceeds in a single step with backside attack and inversion of configuration, while SN1 forms a planar carbocation intermediate first, leading to racemisation.
Concept context
Study carbon-halogen compounds: how they are made, how they react via SN1/SN2 and elimination, their stereochemistry, and their environmental impact.