Answer: Formation of a Meisenheimer complex (carbanion intermediate) followed by departure of Cl-.
- A A simple SN2 backside attack directly on the sp<sup>2</sup> ring carbon bearing chlorine as generally observed
- B Formation of a Meisenheimer complex (carbanion intermediate) followed by departure of Cl-
- C A free radical chain mechanism initiated by homolytic C-Cl cleavage in typical laboratory settings
- D A carbocation (arenium ion) intermediate, as seen in electrophilic substitution under usual circumstances
Correct answer: B. Formation of a Meisenheimer complex (carbanion intermediate) followed by departure of Cl-
Explanation: SNAr proceeds via an addition-elimination mechanism: the nucleophile attacks the carbon bearing the leaving group to form a stable Meisenheimer complex (stabilised by the electron-withdrawing NO₂ groups); then Cl⁻ leaves.
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.