The GATE Grind

GATE 2023 CY – Question 16

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. · 1 mark · Multiple choice

The topicity relationship of Ha and Hb in X, Y and Z are, respectively,

Diagram for GATE 2023 CY question 16
  1. Diastereotopic, Homotopic and Enantiotopic
  2. Homotopic, Enantiotopic and Enantiotopic
  3. Homotopic, Homotopic and Enantiotopic
  4. Diastereotopic, Enantiotopic and Homotopic

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) Homotopic, Enantiotopic and Enantiotopic

Explanation

Apply the isotopic replacement test separately to each pair. InX, proper rotational symmetry interchanges the two hydrogens, so replacement produces the same molecule: homotopic. InY, replacement gives opposite planar chirality; in Z itcreatesopposite axial chirality. Both pairs are enantiotopic.

Therefore **homotopic, enantiotopic, enantiotopic, B**.