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JEE Advanced levelSingle correct optionDifficulty 3 of 3st202

An equimolar mixture of all stereoisomers of 1-bromo-3-chlorocyclohexane is analysed by gas chromatography. Assume ring flips are fast (no separate peaks for conformers), enantiomers are separated only by a chiral stationary phase, and diastereomers are separated by any phase. How many peaks are obtained on (i) an achiral column and (ii) a chiral column?

  1. A(i) 2 and (ii) 4
  2. B(i) 4 and (ii) 4
  3. C(i) 2 and (ii) 2
  4. D(i) 3 and (ii) 4

Answer: A

The four stereoisomers are cis-(1R,3S) and (1S,3R), an enantiomeric pair, and trans-(1R,3R) and (1S,3S), another pair. An achiral phase separates only the diastereomeric sets, cis and trans, giving 2 peaks. A chiral phase also resolves each enantiomeric pair, giving 4 peaks.
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