Answer: 3° > 2° > 1° > methyl.
- A methyl > 1° > 2° > 3°
- B 3° > 2° > 1° > methyl
- C 1° > 2° > 3° > methyl
- D 2° > 3° > 1° > methyl
Correct answer: B. 3° > 2° > 1° > methyl
Explanation: S<sub>N</sub>1 rate depends on carbocation stability, which increases with alkyl substitution, so 3° > 2° > 1° > methyl.
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.