1. Dr. Wolf's CHM 201 & 202 7-1 7.12 Molecules with Multiple Chirality Centers

2. Dr. Wolf's CHM 201 & 202 7-2 maximum number of stereoisomers = 2 n where n = number of structural units capable of stereochemical variation structural units include chirality centers and cis and/or trans double bonds number is reduced to less than 2 n if meso forms are possible How many stereoisomers?

3. Dr. Wolf's CHM 201 & 202 7-3 ExampleExample 4 chirality centers 16 stereoisomers O HOCH 2 CH—CH—CH—CHCH OHOHOHOH

4. Dr. Wolf's CHM 201 & 202 7-4 HO OH H H HO H3CH3CH3CH3C H H CH 2 CH 2 CO 2 H CH 3 H 11 chirality centers 2 11 = 2048 stereoisomers one is "natural" cholic acid a second is the enantiomer of natural cholic acid 2046 are diastereomers of cholic acid Cholic acid

5. Dr. Wolf's CHM 201 & 202 7-5 maximum number of stereoisomers = 2 n where n = number of structural units capable of stereochemical variation structural units include chirality centers and cis and/or trans double bonds number is reduced to less than 2 n if meso forms are possible How many stereoisomers?

6. Dr. Wolf's CHM 201 & 202 7-6 3-Penten-2-ol HO H E R H OH E S H HO Z R H OH S How many stereoisomers? Z

7. Dr. Wolf's CHM 201 & 202 7-7 7.13 Chemical Reactions That Produce Diastereomers

8. Dr. Wolf's CHM 201 & 202 7-8 In order to know understand stereochemistry of product, you need to know two things: (1) stereochemistry of alkene (cis or trans; Z or E) (1) stereochemistry of alkene (cis or trans; Z or E) (2) stereochemistry of mechanism (syn or anti) (2) stereochemistry of mechanism (syn or anti) Stereochemistry of Addition to Alkenes C C + E—Y C C E Y

9. Dr. Wolf's CHM 201 & 202 7-9 Br 2 R S R S meso anti addition to trans-2-butene gives meso diastereomer Bromine Addition to trans-2-Butene

10. Dr. Wolf's CHM 201 & 202 7-10 Br 2 R R S S 50%50% Bromine Addition to cis-2-Butene anti addition to cis-2-butene gives racemic mixture of chiral diastereomer +

11. Dr. Wolf's CHM 201 & 202 7-11 RCO 3 H R R S S syn addition to trans-2-butene gives racemic mixture of chiral diastereomer Epoxidation of trans-2-Butene 50%50% +

12. Dr. Wolf's CHM 201 & 202 7-12 R S R S Epoxidation of cis-2-Butene syn addition to cis-2-butene gives meso diastereomer RCO 3 H meso

13. Dr. Wolf's CHM 201 & 202 7-13 Of two stereoisomers of a particular starting material, each one gives different stereoisomeric forms of the product Related to mechanism: terms such as syn addition and anti addition refer to stereospecificity Stereospecific reaction

14. Dr. Wolf's CHM 201 & 202 7-14. trans-2-butene cis-2-butene trans-2-butene cis-2-butene brominationanti 2R,3R + 2S,3S bromination epoxidation epoxidation anti syn syn meso meso Stereospecific reactions

15. Dr. Wolf's CHM 201 & 202 7-15 A single starting material can give two or more stereoisomeric products, but gives one of them in greater amounts than any other + CH 3 H H 68% 32% Stereoselective reaction CH 3 CH 2 H CH 3 H H H2H2H2H2Pt

16. Dr. Wolf's CHM 201 & 202 7-16 7.14 Resolution of Enantiomers Separation of a racemic mixture into its two enantiomeric forms

17. Dr. Wolf's CHM 201 & 202 7-17 enantiomersC(+)C(+)C(-)C(-)StrategyStrategy

18. Dr. Wolf's CHM 201 & 202 7-18 enantiomersC(+)C(+)C(-)C(-) 2P(+) C(+) C(+)P(+) C(-) C(-)P(+) diastereomers StrategyStrategy

19. Dr. Wolf's CHM 201 & 202 7-19 enantiomersC(+)C(+)C(-)C(-) 2P(+) C(+) C(+)P(+) C(-) C(-)P(+) diastereomers C(+) C(+)P(+) C(-) C(-)P(+) StrategyStrategy

20. Dr. Wolf's CHM 201 & 202 7-20 enantiomersC(+)C(+)C(-)C(-) 2P(+) C(+) C(+)P(+) C(-) C(-)P(+) diastereomers C(+) C(+)P(+) C(-) C(-)P(+) P(+) C(+)C(+) C(-)C(-) StrategyStrategy

21. Dr. Wolf's CHM 201 & 202 7-21 7.15 Stereoregular Polymers atacticisotacticsyndiotactic

22. Dr. Wolf's CHM 201 & 202 7-22 Atactic Polypropylene random stereochemistry of methyl groups attached to main chain (stereorandom) properties not very useful for fibers etc. formed by free-radical polymerization

23. Dr. Wolf's CHM 201 & 202 7-23 Isotactic Polypropylene stereoregular polymer; all methyl groups on same side of main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions

24. Dr. Wolf's CHM 201 & 202 7-24 Syndiotactic Polypropylene stereoregular polymer; methyl groups alternate side-to-side on main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions

25. Dr. Wolf's CHM 201 & 202 7-25 7.16 Chirality Centers Other Than Carbon

26. Dr. Wolf's CHM 201 & 202 7-26 SiliconSilicon Silicon, like carbon, forms four bonds in its stable compounds and many chiral silicon compounds have been resolved SiSi dd a b c a b c

27. Dr. Wolf's CHM 201 & 202 7-27 Nitrogen in amines Pyramidal geometry at nitrogen can produce a chiral structure, but enantiomers equilibrate too rapidly to be resolved NN :: a b c a b c very fast

28. Dr. Wolf's CHM 201 & 202 7-28 Phosphorus in phosphines Pyramidal geometry at phosphorus can produce a chiral structure; pyramidal inversion slower than for amines and compounds of the type shown have been resolved PP :: a b c a b c slow

29. Dr. Wolf's CHM 201 & 202 7-29 Sulfur in sulfoxides Pyramidal geometry at sulfur can produce a chiral structure; pyramidal inversion is slow and compounds of the type shown have been resolved SS :: a b O_ a b O_ slow ++

30. Dr. Wolf's CHM 201 & 202 7-30 End of Chapter 7