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124 Organic Chemistry Solutions Manual pushes the NHTs group downwards. In fact, it is another example of no change in stereochemistry. H H N = N 0 N Ts Ts 0 0 0 Ts Problem 9 Discuss the stereochemistry of these compounds. The diagrams are deliberately poor ones that are ambiguous about stereochemistry - your answer should use good diagrams that show the stereochemistry clearly. NHCO₂Et oH CH=CHPh SMe 0 SMe 0 Me N H Purpose of the problem Practice at spotting stereochemistry and unravelling the different possible stereochemical Suggested solution The first compound is simple: two diastereoisomers, cis and trans; both are chiral. the two the two / NHCO₂Et enantiomers enantiomers of the cis of the trans compound compound Me Me Me Me The second is simple too - the molecule has a plane of symmetry passing through the black dots and is not chiral. No diastereoisomers. The third compound has two stereochemical units: an alkene that can be Z (cis) or E (trans) and that provides two different compounds, or diastereoisomers. There is also a chiral centre so each alkene isomer has two enantiomers. Ph Ph the two the two Ph Ph enantiomers H H enantiomers H H of the E of the Z compound 0 0 compound 0 0 The fourth compound has some symmetry. There are two diastereoisomers with the MeS groups arranged syn or anti (as drawn). One has a plane of symmetry and is a meso compound while the other is chiral. SMe 0 SMe SMe 0 SMe SMe 0 SMe the meso or syn the two enantiomers of the anti compound diastereoisomer not chiral The fifth compound is similar: two diastereoisomers; one is 0 0 0 the two the meso or syn enantiomers diastereoisomer of the anti not chiral compound N N N H H H