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JEE Main levelSingle correct optionDifficulty 2 of 3st013

The isotopically labelled alkene has the deuterium atom and the chlorine atom on the same side of the double bond. Using CIP rules (higher atomic mass wins when atomic numbers tie), the descriptor is

  1. A
  2. B
  3. C
  4. Dit has no descriptor because and are the same element

Answer: A

On one carbon, and have the same atomic number, but has the higher mass number, so . On the other carbon . The two higher priority groups, and , are cis, so the descriptor is .
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