2.3- dibromobutane Fischer projections

The stereochemistry of me.w-2,3-dibromobutane is most easily seen with a Fischer projection ... 

Mirror planes of symmetry are particularly easy to identify from the Fischer projection because this projection is normally the most symmetric conformation. In the first preceding example (propan-2-ol) and in the following example [(2S,3f )-2,3-dibromobutane], the symmetry planes are indicated in red these molecules with symmetry planes cannot be chiral. 

Let us consider how we would relate a three-dimensional formula for 2,3-dibromobutane using solid and dashed wedges to the corresponding Fischer projection formula. 

Doing this with the verticai, eciipsed form of 2,3-dibromobutane ieads to the Fischer projection shown here. 

Write the Fischer projection formulas of the stereoisomers of 2,3-dibromobutane. What relationship exists between the optical activities of these isomers ... 

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