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Chemistry 2100

Chemistry 2100

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Chemistry 2100

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  1. Chemistry 2100 Lecture 8

  2. Enantiomers Enantiomers: Nonsuperposable mirror images. • As an example of a molecule that exists as a pair of enantiomers, consider 2-butanol.

  3. Enantiomers

  4. alanine chiral asymmetric

  5. glycine plane of symmetry achiral

  6. Enantiomers Objects that are nonsuperposable on their mirror images are chiral (from the Greek: cheir, hand). • They show handedness. The most common cause of enantiomerism in organic molecules is the presence of a carbon with four different groups bonded to it. • A carbon with four different groups bonded to it is called a stereocenter.

  7. Drawing Enantiomers

  8. Enantiomers matter! * * *

  9. Properties of Enantiomers

  10. Optical activity

  11. plane-polarized light

  12. plane-polarized light

  13. plane-polarized light

  14. plane-polarized light

  15. plane-polarized light

  16. Fig. 15-6, p. 435

  17. Assigning Rotation dextrorotatory(d)(+) rotation"right-hand isomer" levorotatory(l)(–) rotation"left-hand isomer" (±)or(dl) optically inactiveraceme

  18. Multiple Chiral Centers For a molecule with n stereocenters, the maximum number of possible stereoisomers is 2n. • We have already verified that, for a molecule with one stereocenter, 21 = 2 stereoisomers (one pair of enantiomers) are possible. • For a molecule with two stereocenters, a maximum of 22 = 4 stereoisomers (two pair of enantiomers) are possible. • For a molecule with three stereocenters, a maximum of 23 = 8 stereoisomers (four pairs of enantiomers) are possible, and so forth.

  19. The Four Stereoisomers of a Simple sugar 2R,3S 2S,3R 2R,3R 2S,3S

  20. Fischer Projections

  21. Threose and Erythrose, Fischer-ized

  22. Tartaric Acid COOH COOH meso

  23. COOH COOH meso

  24. COOH COOH meso Meso form

  25. * *

  26. * *

  27. Stereochemical Reactions

  28. * pyruvic acid lactic acid

  29. * pyruvic acid lactic acid

  30. (+) (–)

  31. (+) (–)

  32. (+) (–)

  33. (+) (–)

  34. (+) (–)

  35. (+) (–)

  36. (+) (–)

  37. (+) (–)

  38. But, Biologically… (+)

  39. (+)

  40.  (+)

  41.  (+)

  42.  (+)

  43.    (+)

  44.    (+)

  45. H+    (+)

  46. H+    (+)

  47. Chirality of Biomolecules • Because interactions between molecules in living systems take place in a chiral environment, a molecule and its enantiomer or one of its diastereomers elicit different physiological responses. • As we have seen, (S)-ibuprofen is active as a pain and fever reliever, while its R enantiomer is inactive. • The S enantiomer of naproxen is the active pain reliever, but its R enantiomer is a liver toxin!