Answer: 4.
- A 1
- B 2
- C 4
- D 8
Correct answer: C. 4
Explanation: 2-bromo-3-chlorobutane has two chiral centres; with no meso form possible (different substituents), there are 2² = 4 stereoisomers: (2R,3R), (2S,3S), (2R,3S), and (2S,3R).
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.