The document discusses different types of isomers including constitutional isomers, stereoisomers, enantiomers, and diastereomers. It explains chirality and how molecules can be chiral if they are non-superimposable on their mirror images. The Cahn-Ingold-Prelog system for assigning R/S configurations is described, which involves ranking substituents and determining clockwise or counterclockwise orientation. Enantiomers have opposite optical rotations while diastereomers can have any optical rotation. Molecules can have multiple chiral centers leading to multiple stereoisomers that may be enantiomers or diastereomers.

1. ESTEREOQUÍMICA

2. enantiomersdiastereomersIsomersconstitutionalisomersstereoisomers

4. Molecular Chirality: Enantiomers

5. Chirality A molecule is chiral if its two mirror image forms are not superposable upon one another. A molecule is achiral if its two mirror image forms are superposable.

6. Bromochlorofluoromethane is chiralCl It cannot be superimposed point for point on its mirror image.BrHF

7. Bromochlorofluoromethane is chiralClClBrBrHHFF To show nonsuperimposability, rotate this model 180° around a vertical axis.

8. Bromochlorofluoromethane is chiralClBrClBrHHFF

9. Another look

10. Enantiomersnonsuperimposable mirror images are called enantiomersandare enantiomers with respect to each other

11. Chlorodifluoromethaneis achiral

12. Chlorodifluoromethaneis achiral The two structures are mirror images, but are not enantiomers, because they can be superimposed on each other.

13. The Chirality Center

14. wxyCzThe Chirality Centera carbon atom with fourdifferent groups attached to italso called:chiral centerasymmetric centerstereocenterstereogenic center

15. HFClCBrChirality and chirality centersA molecule with a single chirality center is chiral.Bromochlorofluoromethane is an example.

16. HCH3CH2CH3COHChirality and chirality centersA molecule with a single chirality center is chiral.2-Butanol is another example.

17. CH3CH2CH2CH2CH3CH3CH2CH2CCH2CH3Examples of molecules with 1 chirality centera chiral alkane

18. OHExamples of molecules with 1 chirality centerLinalool, a naturally occurring chiral alcohol

19. H2CCHCH3OExamples of molecules with 1 chirality center1,2-Epoxypropane: a chirality centercan be part of a ringattached to the chirality center are:—H —CH3—OCH2—CH2O

20. CH3HCCH2CH3Examples of molecules with 1 chirality centerLimonene: a chirality center can be part of a ring attached to thechirality center are:—H —CH2CH2—CH2CH=—C=

21. HCH3DCTExamples of molecules with 1 chirality centerChiral as a result of isotopic substitution

22. A molecule with a single chirality centermust be chiral.But, a molecule with two or more chirality centers may be chiral or it may not.

23. Properties of Chiral Molecules:Optical Activity

24. Optical ActivityA substance is optically active if it rotates the plane of polarized light.In order for a substance to exhibit opticalactivity, it must be chiral and one enantiomer must be present in excess of the other.

25. Light has wave properties periodic increase and decrease in amplitude of wave

26. Light optical activity is usually measured using light having a wavelength of 589 nm this is the wavelength of the yellow light from a sodium lamp and is called the D line of sodium

27. Polarized lightordinary (nonpolarized) light consists of many beams vibrating in different planesplane-polarized light consists of only those beams that vibrate in the same plane

28. Nicol prismPolarization of light

29. Rotation of plane-polarized light

30. AbsoluteandRelative Configuration

31. ConfigurationRelative configuration compares the arrangement of atoms in space of one compound with those of another.Absolute configuration is the precise arrangement of atoms in space.

32. ConfigurationRelative configuration compares the arrangement of atoms in space of one compound with those of another.until the 1950s, all configurations were relativeAbsolute configuration is the precise arrangement of atoms in space. we can now determine the absolute configuration of almost any compound

33. CH3CHCH2CH3CH3CHCHCH2OHOHRelative configurationPd[] + 33.2°[] + 13.5°No bonds are made or broken at the chirality centerin this experiment. Therefore, when (+)-3-buten-2-ol and (+)-2-butanol have the same sign of rotation, the arrangement of atoms in space is analogous. The twohave the same relative configuration.

34. HHOHHOOHOHHHTwo possibilitiesH2, PdH2, Pd But in the absence of additional information, we can't tell which structure corresponds to(+)-3-buten-2-ol, and which one to (–)-3-buten-2-ol.

35. HHOHHOOHOHHHTwo possibilitiesH2, PdH2, Pd Nor can we tell which structure corresponds to(+)-2-butanol, and which one to (–)-2-butanol.

36. HHOHHOOHOHHHAbsolute configurationsH2, Pd[] +33.2°[] +13.5°H2, Pd[] –13.5°[] –33.2°

37. CH3CH2CHCH2BrCH3CH2CHCH2OHCH3CH3Relative configurationHBr[] -5.8°[] + 4.0°Not all compounds that have the same relativeconfiguration have the same sign of rotation. No bondsare made or broken at the chirality center in thereaction shown, so the relative positions of the atoms are the same. Yet the sign of rotation changes.

38. The Cahn Ingold PrelogR-S Notational System

39. Two requirements for a systemfor specifying absolute configuration1. need rules for ranking substituents at chirality center in order of decreasing precedence2. need convention for orienting molecule so that order of appearance of substituents can be compared with rank The system that is used was devised by R. S. Cahn, Sir Christopher Ingold, and V. Prelog.

40. The Cahn-Ingold-Prelog Rules1. Rank the substituents at the chirality center according to same rules used in E-Z notation.2. Orient the molecule so that lowest-ranked substituent points away from you.

41. 11433422ExampleOrder of decreasing rank:4 > 3 > 2 > 1

42. The Cahn-Ingold-Prelog Rules1. Rank the substituents at the chirality center according to same rules used in E-Z notation.2. Orient the molecule so that lowest-ranked substituent points away from you. 3. If the order of decreasing precedence traces a clockwise path, the absolute configuration is R. If the path is counterclockwise, the configuration is S.

43. 11433422counterclockwiseclockwiseRSExampleOrder of decreasing rank:43 2

44. HHCH2CH3CH3CH2CHOCOHCH3H3C(S)-2-Butanol(R)-2-ButanolEnantiomers of 2-butanol

45. Very important! Two different compounds with the same sign of rotation need not have the same configuration. Verify this statement by doing Problem. All four compounds have positive rotations. What are their configurations according to the Cahn-Ingold-Prelog rules?

46. HH3CRHHChirality center in a ring—CH2C=C > —CH2CH2 > —CH3 > —H

47. Fischer Projections Purpose of Fischer projections is to show configuration at chirality center without necessity of drawing wedges and dashes or using models.

48. Rules for Fischer projectionsHClBrF Arrange the molecule so that horizontal bonds at chirality center point toward you and vertical bonds point away from you.

49. Rules for Fischer projectionsHBrClF Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back.

50. Rules for Fischer projectionsHBrClF Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back.

51. Physical Properties of Enantiomers

52. Physical properties of enantiomersSame: melting point, boiling point, density, etcDifferent: properties that depend on shape of molecule (biological-physiological properties) can be different

53. OdorCH3CH3OOH3CH3CCH2CH2(–)-Carvonespearmint oil(+)-Carvonecaraway seed oil

54. HH3CCH2CH(CH3)2CCHOOChiral drugsIbuprofen is chiral, but normally sold asa racemic mixture. The S enantiomer is the one responsible for its analgesic and antiinflammatory properties.

55. Chiral MoleculeswithTwo Chirality Centers How many stereoisomers when a particular molecule contains two chirality centers?

56. OCH3CHCHCOHHOOH2,3-Dihydroxybutanoic acid23 What are all the possible R and S combinations of the two chirality centers in this molecule?Carbon-2 R R S SCarbon-3 R S R S

57. OCH3CHCHCOHHOOH2,3-Dihydroxybutanoic acid23 4 Combinations = 4 StereoisomersCarbon-2 R R S SCarbon-3 R S R S

58. OCH3CHCHCOHHOOH2,3-Dihydroxybutanoic acid23 4 Combinations = 4 StereoisomersWhat is the relationship between these stereoisomers?Carbon-2 R R S SCarbon-3 R S R S

59. OCH3CHCHCOHHOOH2,3-Dihydroxybutanoic acid23enantiomers: 2R,3R and 2S,3S2R,3S and 2S,3RCarbon-2 R R S SCarbon-3 R S R S

60. CO2HCO2H[] = -9.5°[] = +9.5°RSHOOHHHenantiomersOHHOHHRSCH3CH3CO2HCO2HSROHHOHHenantiomersOHHHOHRS[] = -17.8°[] = +17.8°CH3CH3

61. OCH3CHCHCOHHOOH2,3-Dihydroxybutanoic acid23but not all relationships are enantiomeric stereoisomers that are not enantiomers are diastereomersCarbon-2 R R S SCarbon-3 R S R S

62. Isomersconstitutionalisomersstereoisomersenantiomersdiastereomers

63. CO2HCO2HRSHOOHHHOHHOHHRSCH3CH3diastereomersCO2HCO2HSROHHOHHOHHHOHRSCH3CH3[] = -9.5°[] = +9.5°enantiomersenantiomers[] = -17.8°[] = +17.8°

64. Fischer Projections recall for Fischer projection: horizontal bonds point toward you; vertical bonds point away staggered conformation does not have correct orientation of bonds for Fischer projectionCO2HCH3

65. Fischer projections transform molecule to eclipsed conformation in order to construct Fischer projection

66. CO2HOHHHOHCH3Fischer projections

67. Two chirality centers in a ringSRSRtrans-1-Bromo-1-chlorocyclopropanenonsuperposable mirror images; enantiomers

68. Two chirality centers in a ringSSRRcis-1-Bromo-1-chlorocyclopropanenonsuperposable mirror images; enantiomers

69. Two chirality centers in a ringSSRRcis-1-Bromo-1-chloro-cyclopropanetrans-1-Bromo-1-chloro-cyclopropanestereoisomers that are notenantiomers; diastereomers