GATE 2024 CY – Question 52

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) regarding P, Q, R, and S is (are):

Cis and trans 4-tert-butylcyclohexyl bromides and alcohols P–S.

P reacts faster than Q with PhSNa in DMF as a solvent.
Q reacts faster than P with NaN3 in DMF as a solvent.
R reacts faster than S when treated with TsCl/Et3N in DCM as a solvent.
R gets oxidized faster than S when reacted with CrO3 in DCM as a solvent.

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Correct answer: (A) P reacts faster than Q with PhSNa in DMF as a solvent.; (D) R gets oxidized faster than S when reacted with CrO3 in DCM as a solvent.

Explanation

The tert-butyl group fixes the chair. P has axial bromide, more favorable for substitution than the equatorial bromide of Q. Axial alcohol R oxidizes more rapidly because elimination from its chromate ester releases axial strain; its oxygen is less accessible for tosylation than S.

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