The Newman projection of 2,3-dichlorobutane viewed along C2-C3 has front carbon (C2): Cl at 12, CH3 at 4, H at 8 o'clock, and rear carbon (C3): Cl at 6, CH3 at 10, H at 2 o'clock. Which statements are correct?

Rotating the rear carbon by 120 deg gives another conformer of the same compound.

The Cl-C-C-Cl dihedral angle is 60 deg.

Rotating the rear carbon by 120 deg gives another conformer of the same compound.

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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3st107

The Newman projection of 2,3-dichlorobutane viewed along C2-C3 has front carbon (C2): Cl at 12, $CH X_{3}$ at 4, H at 8 o'clock, and rear carbon (C3): Cl at 6, $CH X_{3}$ at 10, H at 2 o'clock. Which statements are correct?

AThe compound is meso.
BC3 has the S configuration.
CThe Cl-C-C-Cl dihedral angle is $6 0^{\circ}$ .
DRotating the rear carbon by $12 0^{\circ}$ gives another conformer of the same compound.

Answer: A, B, D

The front carbon is R and the rear carbon is S (opposite descriptors in a symmetric molecule), so the compound is the meso (2R,3S) isomer. The two Cl atoms are at 12 and 6 o'clock, a dihedral angle of

18 0^{\circ}

(anti), so the third statement is false. Rotation about C2-C3 only changes the conformation, so the last statement is true.

Practice Stereoisomerism More on Fischer, Newman and sawhorse projections

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The Newman projection of 2,3-dichlorobutane viewed along C2-C3 has front carbon (C2): Cl at 12, CHX3​ at 4, H at 8 o'clock, and rear carbon (C3): Cl at 6, CHX3​ at 10, H at 2 o'clock. Which statements are correct?

Answer: A, B, D

More questions on Fischer, Newman and sawhorse projections

The Newman projection of 2,3-dichlorobutane viewed along C2-C3 has front carbon (C2): Cl at 12, $CH X_{3}$ at 4, H at 8 o'clock, and rear carbon (C3): Cl at 6, $CH X_{3}$ at 10, H at 2 o'clock. Which statements are correct?