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GATE 2022 CY – Question 57

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 · Numerical answer

The difference between the numbers of gauche-butane interactions in P and Q is ______.

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Correct answer: 1 to 1

Explanation

A consistent chair–chair count includes both ring-junction and methyl gauche interactions. Cis fusion contributes three more ring-junction gauche terms than trans, but the methyl arrangement in trans contributes two additional terms relative to the cis arrangement. The net difference is 3−2=**1**. Counting only the unsubstituted ring junction would give the wrong answer.