Answer: the C-Cl bond has partial double-bond character.
- A chlorine shows a strong +I inductive effect here
- B the benzene ring sterically blocks the nucleophile
- C chlorobenzene has a much higher boiling point
- D the C-Cl bond has partial double-bond character
Correct answer: D. the C-Cl bond has partial double-bond character
Explanation: Resonance of the lone pair into the ring gives the C-Cl bond partial double-bond character (plus sp<sup>2</sup> carbon), making it short, strong and hard to break.
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.