Chemistry 2100

1. Chemistry 2100 Lecture 8

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

4. Enantiomers

5. alanine chiral asymmetric

6. glycine plane of symmetry achiral

7. 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.

8. Drawing Enantiomers

9. Enantiomers matter! * * *

10. Properties of Enantiomers

11.  Optical activity

12. plane-polarized light

13. plane-polarized light

14. plane-polarized light

15. plane-polarized light

16. plane-polarized light

17. Fig. 15-6, p. 435

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

19. 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.

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

21. Fischer Projections

22. Threose and Erythrose, Fischer-ized

23. Tartaric Acid COOH COOH meso

24. COOH COOH meso

25. COOH COOH meso Meso form

26. * *

27. * *

28. Stereochemical Reactions

29. * pyruvic acid lactic acid

30. * pyruvic acid lactic acid

31. (+) (–)

32. (+) (–)

33. (+) (–)

34. (+) (–)

35. (+) (–)

36. (+) (–)

37. (+) (–)

38. (+) (–)

39. But, Biologically… (+)

40. (+)

41.  (+)

42.  (+)

43.  (+)

44.    (+)

45.    (+)

46. H+    (+)

47. H+    (+)

48. 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!