CHAPTER 4: Question 8

Simple Answers

A must have the structure shown below in which the configuration of the two outer strereocentres is S, but the two sterocentres at the alcohol bearing carbon atoms can have any configuration. Thus there are three possible structures for A which will give B as the only product, the SSSS, SRSS, and SRRS isomers of the structure
shown below. Of the other stereoisomers of A, four (the RRRR, RSRR, and RSSR isomers) will give the enantiomer of B as the only product. The remaining stereoisomers of A (SSRR, SRSR, SSSR, and SRRR) will give a 1:1 mixture of B and the enantiomer of B.

Note that due to the symmtrical nature of A, there are fewer than the 16 maximum possible stereoisomers.

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