A Newman projection of 2,3-dibromobutane, viewed along C2 (front) to C3 (rear), shows: front carbon C2 with CH3 at 12 o'clock, Br at 4 o'clock, H at 8 o'clock; rear carbon C3 with CH3 at 6 o'clock, Br at 10 o'clock, H at 2 o'clock. The compound is

meso-(2S,3R)-2,3-dibromobutane, optically inactive

(2R,3R)-2,3-dibromobutane, optically active

(2S,3S)-2,3-dibromobutane, optically active

racemic mixture of (2R,3R) and (2S,3S)

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JEE Advanced levelSingle correct optionDifficulty 3 of 3st157

A Newman projection of 2,3-dibromobutane, viewed along C2 (front) to C3 (rear), shows: front carbon C2 with $CH X_{3}$ at 12 o'clock, Br at 4 o'clock, H at 8 o'clock; rear carbon C3 with $CH X_{3}$ at 6 o'clock, Br at 10 o'clock, H at 2 o'clock. The compound is

Ameso-(2S,3R)-2,3-dibromobutane, optically inactive
B(2R,3R)-2,3-dibromobutane, optically active
C(2S,3S)-2,3-dibromobutane, optically active
Dracemic mixture of (2R,3R) and (2S,3S)

Answer: A

The conformation is staggered with the methyls anti (12 and 6 o'clock) and the bromines anti (4 and 10 o'clock). With CIP priorities Br > C >

CH X_{3}

> H, coordinate analysis gives C2 = S and C3 = R. A (2S,3R) compound is meso, with a centre of inversion in this anti conformation, hence optically inactive.

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A Newman projection of 2,3-dibromobutane, viewed along C2 (front) to C3 (rear), shows: front carbon C2 with CHX3​ at 12 o'clock, Br at 4 o'clock, H at 8 o'clock; rear carbon C3 with CHX3​ at 6 o'clock, Br at 10 o'clock, H at 2 o'clock. The compound is

Answer: A

More questions on Conformational analysis of ethane, butane and cyclohexane

A Newman projection of 2,3-dibromobutane, viewed along C2 (front) to C3 (rear), shows: front carbon C2 with $CH X_{3}$ at 12 o'clock, Br at 4 o'clock, H at 8 o'clock; rear carbon C3 with $CH X_{3}$ at 6 o'clock, Br at 10 o'clock, H at 2 o'clock. The compound is