A Fischer projection of 2,3-dichlorobutane has the vertical chain, top to bottom: CH3, C2, C3, CH3. On C2 the right group is Cl and the left group is H; on C3 the right group is Cl and the left group is H. Which statements are correct?

C2 and C3 have opposite CIP descriptors.

Exchanging Cl and H on C3 only gives a chiral diastereomer of this compound.

C2 and C3 have opposite CIP descriptors.

The compound is optically active.

Exchanging Cl and H on C3 only gives a chiral diastereomer of this compound.

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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3st053

A Fischer projection of 2,3-dichlorobutane has the vertical chain, top to bottom: $CH X_{3}$ , C2, C3, $CH X_{3}$ . On C2 the right group is $Cl$ and the left group is $H$ ; on C3 the right group is $Cl$ and the left group is $H$ . Which statements are correct?

AC2 and C3 have opposite CIP descriptors.
BThe compound is optically active.
CExchanging $Cl$ and $H$ on C3 only gives a chiral diastereomer of this compound.
DThe compound is meso.

Answer: A, C, D

With both

Cl

atoms on the same side (right) of a symmetric chain, the projection has a horizontal mirror line between C2 and C3, so the compound is meso (A) and the centres are

(2 R, 3 S)

with opposite descriptors (B, confirmed by assigning each centre). A meso compound is optically inactive (C is wrong). Exchanging

Cl

and

H

on one centre gives

(2 R, 3 R)

(2 S, 3 S)

, a chiral stereoisomer that is not the mirror image of the meso form, i.e. a chiral diastereomer (D). Correct: A, B and D.

Practice Stereoisomerism More on Chirality, enantiomers and R/S configuration

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A Fischer projection of 2,3-dichlorobutane has the vertical chain, top to bottom: CHX3​, C2, C3, CHX3​. On C2 the right group is Cl and the left group is H; on C3 the right group is Cl and the left group is H. Which statements are correct?

Answer: A, C, D

More questions on Chirality, enantiomers and R/S configuration

A Fischer projection of 2,3-dichlorobutane has the vertical chain, top to bottom: $CH X_{3}$ , C2, C3, $CH X_{3}$ . On C2 the right group is $Cl$ and the left group is $H$ ; on C3 the right group is $Cl$ and the left group is $H$ . Which statements are correct?