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  • 1. ESTEREOQUÍMICA
  • 2. enantiomers
    diastereomers
    Isomers
    constitutional
    isomers
    stereoisomers
  • 3.
  • 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 chiral
    Cl
    It cannot be superimposed point for point on its mirror image.
    Br
    H
    F
  • 7. Bromochlorofluoromethane is chiral
    Cl
    Cl
    Br
    Br
    H
    H
    F
    F
    To show nonsuperimposability, rotate this model 180° around a vertical axis.
  • 8. Bromochlorofluoromethane is chiral
    Cl
    Br
    Cl
    Br
    H
    H
    F
    F
  • 9. Another look
  • 10. Enantiomers
    nonsuperimposable mirror images are called enantiomers
    and
    are 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. w
    x
    y
    C
    z
    The Chirality Center
    a carbon atom with fourdifferent groups attached to it
    also called:
    chiral centerasymmetric centerstereocenter
    stereogenic center
  • 15. H
    F
    Cl
    C
    Br
    Chirality and chirality centers
    A molecule with a single chirality center is chiral.
    Bromochlorofluoromethane is an example.
  • 16. H
    CH3
    CH2CH3
    C
    OH
    Chirality and chirality centers
    A molecule with a single chirality center is chiral.
    2-Butanol is another example.
  • 17. CH3
    CH2CH2CH2CH3
    CH3CH2CH2
    C
    CH2CH3
    Examples of molecules with 1 chirality center
    a chiral alkane
  • 18. OH
    Examples of molecules with 1 chirality center
    Linalool, a naturally occurring chiral alcohol
  • 19. H2C
    CHCH3
    O
    Examples of molecules with 1 chirality center
    1,2-Epoxypropane: a chirality center
    can be part of a ring
    attached to the chirality center are:
    —H
    —CH3
    —OCH2
    —CH2O
  • 20. CH3
    H
    C
    CH2
    CH3
    Examples of molecules with 1 chirality center
    Limonene: a chirality center can be part of a ring
    attached to thechirality center are:
    —H
    —CH2CH2
    —CH2CH=
    —C=
  • 21. H
    CH3
    D
    C
    T
    Examples of molecules with 1 chirality center
    Chiral 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 Activity
    A 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 light
    ordinary (nonpolarized) light consists of many beams vibrating in different planes
    plane-polarized light consists of only those beams that vibrate in the same plane
  • 28. Nicol prism
    Polarization of light
  • 29.
    Rotation of plane-polarized light
  • 30. AbsoluteandRelative Configuration
  • 31. Configuration
    Relative 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. Configuration
    Relative configuration compares the arrangement of atoms in space of one compound with those of another.until the 1950s, all configurations were relative
    Absolute configuration is the precise arrangement of atoms in space. we can now determine the absolute configuration of almost any compound
  • 33. CH3CHCH2CH3
    CH3CHCH
    CH2
    OH
    OH
    Relative configuration
    Pd
    [] + 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. H
    HO
    H
    HO
    OH
    OH
    H
    H
    Two possibilities
    H2, Pd
    H2, 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. H
    HO
    H
    HO
    OH
    OH
    H
    H
    Two possibilities
    H2, Pd
    H2, Pd
    Nor can we tell which structure corresponds to(+)-2-butanol, and which one to (–)-2-butanol.
  • 36. H
    HO
    H
    HO
    OH
    OH
    H
    H
    Absolute configurations
    H2, Pd
    [] +33.2°
    [] +13.5°
    H2, Pd
    [] –13.5°
    [] –33.2°
  • 37. CH3CH2CHCH2Br
    CH3CH2CHCH2OH
    CH3
    CH3
    Relative configuration
    HBr
    [] -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 configuration
    1. need rules for ranking substituents at chirality center in order of decreasing precedence
    2. 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 Rules
    1. 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. 1
    1
    4
    3
    3
    4
    2
    2
    Example
    Order of decreasing rank:4 > 3 > 2 > 1
  • 42. The Cahn-Ingold-Prelog Rules
    1. 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. 1
    1
    4
    3
    3
    4
    2
    2
    counterclockwise
    clockwise
    R
    S
    Example
    Order of decreasing rank:43 2
  • 44. H
    H
    CH2CH3
    CH3CH2
    C
    HO
    C
    OH
    CH3
    H3C
    (S)-2-Butanol
    (R)-2-Butanol
    Enantiomers 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. H
    H3C
    R
    H
    H
    Chirality 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 projections
    H
    Cl
    Br
    F
    Arrange the molecule so that horizontal bonds at chirality center point toward you and vertical bonds point away from you.
  • 49. Rules for Fischer projections
    H
    Br
    Cl
    F
    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 projections
    H
    Br
    Cl
    F
    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 enantiomers
    Same: melting point, boiling point, density, etc
    Different: properties that depend on shape of molecule (biological-physiological properties) can be different
  • 53. Odor
    CH3
    CH3
    O
    O
    H3C
    H3C
    CH2
    CH2
    (–)-Carvonespearmint oil
    (+)-Carvonecaraway seed oil
  • 54. H
    H3C
    CH2CH(CH3)2
    C
    C
    HO
    O
    Chiral drugs
    Ibuprofen 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. O
    CH3CHCHCOH
    HO
    OH
    2,3-Dihydroxybutanoic acid
    2
    3
    What are all the possible R and S combinations of the two chirality centers in this molecule?
    Carbon-2 R R S S
    Carbon-3 R S R S
  • 57. O
    CH3CHCHCOH
    HO
    OH
    2,3-Dihydroxybutanoic acid
    2
    3
    4 Combinations = 4 Stereoisomers
    Carbon-2 R R S S
    Carbon-3 R S R S
  • 58. O
    CH3CHCHCOH
    HO
    OH
    2,3-Dihydroxybutanoic acid
    2
    3
    4 Combinations = 4 Stereoisomers
    What is the relationship between these stereoisomers?
    Carbon-2 R R S S
    Carbon-3 R S R S
  • 59. O
    CH3CHCHCOH
    HO
    OH
    2,3-Dihydroxybutanoic acid
    2
    3
    enantiomers: 2R,3R and 2S,3S
    2R,3S and 2S,3R
    Carbon-2 R R S S
    Carbon-3 R S R S
  • 60. CO2H
    CO2H
    [] = -9.5°
    [] = +9.5°
    R
    S
    HO
    OH
    H
    H
    enantiomers
    OH
    HO
    H
    H
    R
    S
    CH3
    CH3
    CO2H
    CO2H
    S
    R
    OH
    HO
    H
    H
    enantiomers
    OH
    H
    HO
    H
    R
    S
    [] = -17.8°
    [] = +17.8°
    CH3
    CH3
  • 61. O
    CH3CHCHCOH
    HO
    OH
    2,3-Dihydroxybutanoic acid
    2
    3
    but not all relationships are enantiomeric
    stereoisomers that are not enantiomers are diastereomers
    Carbon-2 R R S S
    Carbon-3 R S R S
  • 62. Isomers
    constitutional
    isomers
    stereoisomers
    enantiomers
    diastereomers
  • 63. CO2H
    CO2H
    R
    S
    HO
    OH
    H
    H
    OH
    HO
    H
    H
    R
    S
    CH3
    CH3
    diastereomers
    CO2H
    CO2H
    S
    R
    OH
    HO
    H
    H
    OH
    H
    HO
    H
    R
    S
    CH3
    CH3
    [] = -9.5°
    [] = +9.5°
    enantiomers
    enantiomers
    [] = -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 projection
    CO2H
    CH3
  • 65. Fischer projections
    transform molecule to eclipsed conformation in order to construct Fischer projection
  • 66. CO2H
    OH
    H
    H
    OH
    CH3
    Fischer projections
  • 67. Two chirality centers in a ring
    S
    R
    S
    R
    trans-1-Bromo-1-chlorocyclopropane
    nonsuperposable mirror images; enantiomers
  • 68. Two chirality centers in a ring
    S
    S
    R
    R
    cis-1-Bromo-1-chlorocyclopropane
    nonsuperposable mirror images; enantiomers
  • 69. Two chirality centers in a ring
    S
    S
    R
    R
    cis-1-Bromo-1-chloro-cyclopropane
    trans-1-Bromo-1-chloro-cyclopropane
    stereoisomers that are notenantiomers; diastereomers