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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3st286

The compound shown is one stereoisomer of tartaric acid (2,3-dihydroxybutanedioic acid). Which statements about it are correct?

  1. AIn its anti (staggered) conformation it has a centre of symmetry
  2. BIn its eclipsed conformation it has a plane of symmetry
  3. CIts configuration can be written as (2R,3S)
  4. DIts enantiomer is (2S,3R)-tartaric acid

Answer: A, B, C

Assigning CIP priorities (OH, then COOH, then CH(OH)COOH, then H) gives at one centre and at the other, so the compound is meso-tartaric acid, (2R,3S). Because C2 and C3 carry identical groups with opposite configurations, the eclipsed conformation has a mirror plane between C2 and C3, and the anti conformation has an inversion centre at the midpoint of the C2-C3 bond. Either element makes the molecule achiral. Reflecting (2R,3S) gives (2S,3R), which is the same compound after renumbering, so the meso acid has no enantiomer; statement (D) is wrong.
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