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7.13 Reactions That Produce Diastereomers

7.13 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 Reactions That Produce Diastereomers

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  1. 7.13 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. 7.12 anti addition to trans-2-butene gives meso diastereomer S R Br2 S R meso

  4. Bromine Addition to cis-2-ButeneFig. 7.12 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 7.21 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 7.21 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(+) P(+) C(+) C(-) C(+)P(+) 2P(+) C(-)P(+) C(+)P(+) C(-)P(+) P(+) diastereomers C(-) Strategy enantiomers

  12. 7.15Stereoregular Polymers atactic isotactic syndiotactic

  13. Atactic Polypropylene Random stereochemistry of methyl groups attached to main chain (stereorandom) Properties not very useful for fibers etc. Formed by free-radical polymerization

  14. Isotactic Polypropylene Stereoregular polymer; all methyl groups onsame side of main chain Useful properties Prepared by coordination polymerization under Ziegler-Natta conditions

  15. Syndiotactic Polypropylene Stereoregular polymer; methyl groups alternate side-to-side on main chain Useful properties Prepared by coordination polymerization under Ziegler-Natta conditions

  16. 7.16Chirality CentersOther Than Carbon

  17. 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

  18. 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

  19. 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

  20. 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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