Answer: it solvates the cation, freeing the nucleophile.
- A it solvates the nucleophile very strongly
- B it solvates the cation, freeing the nucleophile
- C it hydrogen-bonds tightly to the nucleophile
- D it lowers the nucleophile concentration sharply
Correct answer: B. it solvates the cation, freeing the nucleophile
Explanation: Aprotic solvents solvate the cation but leave the anionic nucleophile poorly solvated (naked), raising its reactivity in S<sub>N</sub>2.
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.