1. Chemistry 2100 Lecture 8

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

4. Enantiomers

5. chiral asymmetric alanine

6. plane of symmetry achiral glycine

7. Enantiomers chiral 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. stereocenter –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

17. Fig. 15-6, p. 435

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

19. Multiple Chiral Centers n 2 n For a molecule with n stereocenters, the maximum number of possible stereoisomers is 2 n. –We have already verified that, for a molecule with one stereocenter, 2 1 = 2 stereoisomers (one pair of enantiomers) are possible. –For a molecule with two stereocenters, a maximum of 2 2 = 4 stereoisomers (two pair of enantiomers) are possible. –For a molecule with three stereocenters, a maximum of 2 3 = 8 stereoisomers (four pairs of enantiomers) are possible, and so forth.

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

21. Fischer Projections

22. Threose and Erythrose, Fischer-ized

23. meso COOH Tartaric Acid

24. meso COOH

25. meso Meso form

26. **

27. **

28. Stereochemical Reactions

29. * pyruvic acidlactic 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+H+   

47. H+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!