Two compounds of constitution CH3-CH(OH)-CH(Cl)-CH3 are drawn as Fischer projections with the vertical chain C1 (CH3, top), C2, C3, C4 (CH3, bottom). Compound X: C2 has left OH and right H; C3 has left H and right Cl. Compound Y: C2 has left H and right Cl; C3 has left H and right OH. X and Y are:

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JEE Advanced levelSingle correct optionDifficulty 3 of 3st083

Two compounds of constitution $CH X_{3} - CH (OH) - CH (Cl) - CH X_{3}$ are drawn as Fischer projections with the vertical chain C1 ( $CH X_{3}$ , top), C2, C3, C4 ( $CH X_{3}$ , bottom). Compound X: C2 has left OH and right H; C3 has left H and right Cl. Compound Y: C2 has left H and right Cl; C3 has left H and right OH. X and Y are:

Adiastereomers
Benantiomers
Cidentical
Dconstitutional isomers

Answer: A

Y has Cl on C2 and OH on C3, so rotate Y by

18 0^{\circ}

in the plane to read it from the other end: C2 (old C3) has left OH, right H, and C3 (old C2) has left Cl, right H. Compare with X: C2 is identical (left OH, right H), but C3 has Cl on the left in Y and on the right in X. Exactly one of the two centres is inverted, so X and Y are diastereomers.

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Answer: A

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