Answer: Br.
- A H
- B C
- C O
- D Br
Correct answer: D. Br
Explanation: CIP priority is based on atomic number: Br (35) > O (8) > C (6) > H (1). Bromine has the highest atomic number and therefore the highest priority.
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.