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GATE 2021 CY – Question 30

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 · Numerical answer

Among the following eight compounds, the number of compound(s) which can exhibit stereoisomerism is _______.

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Correct answer: 6 to 6

Explanation

Number the drawings left to right across the upper row, then the lower row. Compounds 1 and 2 contain stereogenic alcohol/ring carbons; 4 can show spiro chirality; 5 contains a stereogenic side-chain carbon; 6 has hindered biaryl rotation giving atropisomers; and 8 has cis/trans ring substitution. Compound 3 is the symmetric cage diketone and 7 has two identical methyl groups at one allene terminus, so neither contributes.

Thus the count is **6**.