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NEET levelSingle correct optionDifficulty 1 of 3st279

The compound shown is trans-1,4-dimethylcyclohexane. It is optically inactive because

  1. Ait has a plane of symmetry passing through C1 and C4
  2. Bit is a racemic mixture of two enantiomers
  3. Cit contains no sp3 carbon atom
  4. Dit interconverts rapidly with its enantiomer by ring flipping

Answer: A

In 1,4-dimethylcyclohexane, C1 and C4 are not stereocentres: the two ring paths from C1 to C4 are identical, so each carbon carries two equivalent ring arms. The cis and trans isomers are diastereomers but both are achiral. The trans isomer shown has a mirror plane containing C1, C4 and both methyl groups, so it is superimposable on its mirror image. It is a single achiral compound, not a racemate, so it does not rotate plane-polarised light.
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