Answer: stabilises the anionic intermediate by resonance.
- A lengthens the carbon-chlorine bond
- B increases the electron density of the ring
- C stabilises the anionic intermediate by resonance
- D acts as a strong electron-donating group
Correct answer: C. stabilises the anionic intermediate by resonance
Explanation: At ortho/para positions the -NO<sub>2</sub> group withdraws the negative charge of the carbanion (Meisenheimer) intermediate by resonance, easing S<sub>N</sub>Ar.
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.