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7.13 Chemical Reactions That Produce Diastereomers

7.13 Chemical Reactions That Produce Diastereomers. +. E—Y. E. Y. C. C. C. C. Stereochemistry of Addition to Alkenes. In order to know understand stereochemistry of product, you need to know two things: (1) stereochemistry of alkene (cis or trans; Z or E)

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7.13 Chemical Reactions That Produce Diastereomers

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  1. 7.13 Chemical Reactions That Produce Diastereomers

  2. + E—Y E Y C C C C Stereochemistry of Addition to Alkenes In order to know understand stereochemistry of product, you need to know two things: (1) stereochemistry of alkene (cis or trans; Z or E) (2) stereochemistry of mechanism (syn or anti)

  3. Bromine Addition to trans-2-ButeneFig. 7.14 (p 284) anti addition to trans-2-butene gives meso diastereomer S R Br2 S R meso

  4. Bromine Addition to cis-2-ButeneFig. 7.15 (p 285) anti addition to cis-2-butene gives racemic mixture of chiral diastereomer S R Br2 + S R 50% 50%

  5. Epoxidation of trans-2-ButeneProblem 7.17 (p 285) S syn addition to trans-2-butene gives racemic mixture of chiral diastereomer R RCO3H + R S 50% 50%

  6. Epoxidation of cis-2-ButeneProblem 7.17 (p 285) syn addition to cis-2-butene gives meso diastereomer R S RCO3H S R meso

  7. Stereospecific reaction of two stereoisomers of a particular starting material, each one gives differentstereoisomeric forms of the product related to mechanism: terms such assyn addition and anti addition refer tostereospecificity

  8. cis-2-butene bromination anti 2R,3R + 2S,3S trans-2-butene bromination anti meso cis-2-butene epoxidation syn meso trans-2-butene epoxidation syn 2R,3R + 2S,3S Stereospecific reaction .

  9. H H CH3 H2 CH3 CH3 Pt CH2 H Stereoselective reaction a single starting material can give two or morestereoisomeric products, but gives one of themin greater amounts than any other H CH3 + H CH3 32% 68%

  10. 7.14 Resolution of Enantiomers separation of a racemic mixture into its two enantiomeric forms

  11. C(+) C(-) Strategy enantiomers

  12. C(+) C(-) C(+)P(+) C(-)P(+) Strategy enantiomers 2P(+) diastereomers

  13. C(+) C(-) C(+)P(+) C(-)P(+) Strategy enantiomers C(+)P(+) 2P(+) C(-)P(+) diastereomers

  14. C(+) C(-) C(+)P(+) C(-)P(+) Strategy C(+) enantiomers P(+) C(+)P(+) 2P(+) C(-)P(+) P(+) diastereomers C(-)

  15. 7.15Stereoregular Polymers atactic isotactic syndiotactic

  16. Atactic Polypropylene random stereochemistry of methyl groups attached to main chain (stereorandom) properties not very useful for fibers etc. formed by free-radical polymerization

  17. Isotactic Polypropylene stereoregular polymer; all methyl groups onsame side of main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions

  18. Syndiotactic Polypropylene stereoregular polymer; methyl groups alternate side-to-side on main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions

  19. 7.16Stereogenic CentersOther Than Carbon

  20. Silicon b b silicon, like carbon, forms four bonds in its stable compounds and many chiral silicon compounds have been resolved a a d d Si Si c c

  21. Nitrogen in amines b b pyramidal geometry at nitrogen can produce a chiral structure, but enantiomers equilibrate too rapidly to be resolved very fast a a : : N N c c

  22. Phosphorus in phosphines b b pyramidal geometry at phosphorus can produce a chiral structure; pyramidal inversion slower than for amines and compounds of the type shown have been resolved slow a a : : P P c c

  23. Sulfur in sulfoxides b b pyramidal geometry at sulfur can produce a chiral structure; pyramidal inversion is slow and compounds of the type shown have been resolved slow a a : : + + S S O_ O_

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