Answer: Cl• + O 3 → ClO• + O 2 ; then ClO• + O• → Cl• + O 2 ; the Cl• is regenerated catalytically destroying thousands of O 3 molecules.
- A Cl• + O<sub>3</sub> → ClO• + O<sub>2</sub>; then ClO• + O• → Cl• + O<sub>2</sub>; the Cl• is regenerated catalytically destroying thousands of O<sub>3</sub> molecules
- B Cl• directly and largely irreversibly reacts with atmospheric N<sub>2</sub> gas to permanently form nitrogen trichloride during normal conditions
- C Cl• is mostly consumed by forming stable HCl gas with little further ozone destruction occurring afterward, as generally observed
- D Cl• reacts harmlessly with O<sub>2</sub> gas to form a fairly stable, largely unreactive ClO<sub>2</sub> species in typical laboratory settings
Correct answer: A. Cl• + O<sub>3</sub> → ClO• + O<sub>2</sub>; then ClO• + O• → Cl• + O<sub>2</sub>; the Cl• is regenerated catalytically destroying thousands of O<sub>3</sub> molecules
Explanation: This is the catalytic ozone depletion cycle. Cl• is not consumed; it is regenerated after each cycle, meaning a single Cl atom can destroy up to 100,000 ozone molecules before being deactivated.
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.