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GATE 2024 CY – Question 55

Organic Chemistry · Stereochemistry: Chirality and symmetry of organic molecules with or without chiral centres and determination of their absolute configurations and optical purity. Relative stereochemistry in compounds having more than one stereogenic centre. Homotopic, enantiotopic and diastereotopic atoms, groups and faces. Conformational analysis of acyclic and cyclic compounds. Geometrical isomerism and optical isomerism. Configurational and conformational effects, atropisomerism, and neighbouring group participation on reactivity and selectivity/specificity. Stereoselective and stereospecific synthesis. Enantiomeric excess. · 2 marks · Multiple select

The correct statement(s) about the relationship for the H-atoms in the following compounds is (are):

Stereochemical hydrogen labels H1–H8 on two bicyclic compounds.
  1. H1 and H3 are enantiotopic; H2 and H3 are diastereotopic.
  2. H1 and H3 are diastereotopic; H2 and H3 are enantiotopic.
  3. H5 and H7 are enantiotopic; H6 and H7 are homotopic.
  4. H5 and H7 are homotopic; H6 and H7 are enantiotopic.

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Show answer and explanation

Correct answer: (A) H1 and H3 are enantiotopic; H2 and H3 are diastereotopic.; (C) H5 and H7 are enantiotopic; H6 and H7 are homotopic.

Explanation

The replacement test makes H1/H3 enantiotopic but H2/H3 diastereotopic in the first bicyclic framework. In the second, H6/H7 are symmetry-related by a proper rotation and homotopic, whereas H5/H7 are enantiotopic.

Official GATE 2024 answer key: https://gate2026.iitg.ac.in/doc/download/2024/CYFinalAnswerKey.pdf