In a Fischer projection of 2,3-dibromobutane the vertical chain is C1 (CH3, top), C2, C3, C4 (CH3, bottom). C2: left H, right Br. C3: left H, right Br. This isomer is:

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In a Fischer projection of 2,3-dibromobutane the vertical chain is C1 ( $CH X_{3}$ , top), C2, C3, C4 ( $CH X_{3}$ , bottom). C2: left H, right Br. C3: left H, right Br. This isomer is:

Aerythro, (2R,3R), chiral
Bthreo, (2S,3R), meso
Cerythro, (2S,3R), meso
Dthreo, (2R,3R), chiral

Answer: C

Identical groups on the same side of a Fischer projection are called erythro, and this arrangement has an internal mirror plane (eclipsed form). Assigning CIP priorities gives S at C2 and R at C3, so the compound is (2S,3R), the meso form. A threo isomer would have the two Br on opposite sides and would be (R,R) or (S,S).

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In a Fischer projection of 2,3-dibromobutane the vertical chain is C1 (CHX3​, top), C2, C3, C4 (CHX3​, bottom). C2: left H, right Br. C3: left H, right Br. This isomer is:

Answer: C

More questions on Diastereomers, meso compounds and counting stereoisomers

In a Fischer projection of 2,3-dibromobutane the vertical chain is C1 ( $CH X_{3}$ , top), C2, C3, C4 ( $CH X_{3}$ , bottom). C2: left H, right Br. C3: left H, right Br. This isomer is: