Meso Compounds Have Asymmetric Centers but Are Optically Inactive

Indicate whether each of the structures in the second row is an enantiomer of, is a diastereomer of, or is identical to the structure in the top row. 

13 MESO COMPOUNDS HAVE ASYMMETRIC CENTERS BUT ARE OPTICALLY INACTIVE 

In the examples we have just seen, all the compounds with two asymmetric centers had four stereoisomers. However, some compounds with two asymmetric centers have only three stereoisomers. 

The following is an example of a compound with two asymmetric centers that has only three stereoisomers. 

The missing stereoisomer is the mirror image of 1 because 1 and its mirror image are the same molecule. This can be seen more clearly when the perspective formulas are drawn in eclipsed conformations or when Fischer projections are used. 

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Meso Compounds Have Asymmetric Centers but Are Optically Inactive 169... 

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