Answer: CH 3 Cl > CH 3 F > CH 3 Br > CH 3 I.
- A CH<sub>3</sub>F > CH<sub>3</sub>Cl > CH<sub>3</sub>Br > CH<sub>3</sub>I
- B CH<sub>3</sub>I > CH<sub>3</sub>Br > CH<sub>3</sub>Cl > CH<sub>3</sub>F
- C CH<sub>3</sub>Br > CH<sub>3</sub>Cl > CH<sub>3</sub>F > CH<sub>3</sub>I
- D CH<sub>3</sub>Cl > CH<sub>3</sub>F > CH<sub>3</sub>Br > CH<sub>3</sub>I
Correct answer: D. CH<sub>3</sub>Cl > CH<sub>3</sub>F > CH<sub>3</sub>Br > CH<sub>3</sub>I
Explanation: Dipole moment reflects bond polarity and bond length together; the measured order is CH<sub>3</sub>Cl > CH<sub>3</sub>F > CH<sub>3</sub>Br > CH<sub>3</sub>I.
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.