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GATE 2024 CY – Question 15

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

Among the following, the chiral compound is

Structures P, Q, R and S showing cumulenes and stereochemical bonds.
  1. P
  2. Q
  3. R
  4. S

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Show answer and explanation

Correct answer: (B) Q

Explanation

Q is an allene with different substituents at each terminus, so its perpendicular terminal planes give axial chirality. R has three cumulated double bonds and coplanar terminal substituents; P and S have internal symmetry.