Stereochemistry

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Stereochemistry

• Stereochemistry refers to the
• 3-dimensional properties and reactions of
  molecules. It has its own language and terms
  that need to be learned in order to fully
  communicate and understand the concepts.

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Definitions

• Stereoisomers compounds with the same
  connectivity, different arrangement in space
• Enantiomers stereoisomers that are
  non- superimposible mirror images only
  properties that differ are direction ( or -)
  of optical rotation
• Diastereomers stereoisomers that are not
  mirror images different compounds with
  different physical properties

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More Definitions

• Asymmetric center sp3 carbon with 4 different
  groups attached
• Optical activity the ability to rotate the
  plane of plane polarized light
• Chiral compound a compound that is optically
  active (achiral compound will not rotate light)
• Polarimeter device that measures the optical
  rotation of the chiral compound

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Plane-Polarized Light

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Plane-Polarized Light through an Achiral Compound
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Plane-Polarized Light through a Chiral Compound
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Polarimeter Measures Optical Rotation
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Specific Rotation, a

• a a / cl
• a observed rotation
• c concentration in g/mL
• l length of tube in dm
• Dextrorotary designated as d or (), clockwise
  rotation Levorotary designated as l or (-),
  counter- clockwise rotation

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Specific Rotations of some Common Organic
Compounds

• Compound a centers
• Penicillin V 233.0 3
• Sucrose 66.5 10 
• Camphor 44.3 2
• MSG 25.5 1
• Cholesterol -31.3 8
• Morphine -132.0 5

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Chirality CenterCarbon has four different groups
attached
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Enantiomers nonsuperimposible mirror images
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Enantiomeric Excess(Optical Purity)
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Biological Activity
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SSRI Efficacy depends on Stereochemistry
Lexapro and Celexa are both prescription
medications classified as selective serotonin
reuptake inhibitors, licensed to treat depression.
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Absolute Configuration
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Assign Priority to each Group on Asymmetric Center
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Lactic Acid
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C.I.P. Priorities
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Fischer Projections
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Assigning Absolute Configuration to Fischer
Projections
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Rotation of the Projection 90oReverses Absolute
Configuration
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Exercise

1. Assign R/S configurations to the ff molecules
2. Draw a tetrahedral representation of
   (S)-2-hydroxypentane.

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• Lexapro and Celexa are formulations of an
  anti-depressant drug. Celexa was available first
  and is a mixture of R and S enantiomers of
  citalopram. Lexapro is just the S enantiomer of
  citalopram. Draw the molecular structure of each
  enantiomer.

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Celexa was available first and is a mixture of R
and S enantiomers of citalopram. Lexapro is just
the S enantiomer of citalopram. Which one is
Lexapro? Which one is Celexa?
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DiastereomersStereoisomers That Are Not Mirror
Images
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Fischer Projections with 2 Chiral Centers
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2 Chiral Centers4 Stereoisomers
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Identical, Enantiomers or Diastereomers?
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Tartaric Acids
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Racemic Mixture
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Meso CompoundInternal Plane of Symmetry
Optically Inactive
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2,3,4-trichlorohexaneHow many stereoisomers?
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n 3 2n 8
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A Carbohydrate
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Internal Planes of Symmetry
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Asymmetric Centers on Rings
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Which are meso compounds?
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Reactions that Generate Chirality Centers
Hydrogenation, syn
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BrominationTrans is formed exclusivelyNo Meso
is formed (cis)
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Bromonium Ion is Opened Equally from Both Sides
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trans alkene anti addition MESO
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cis Alkene anti addition racemic mixture
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Brominations Often Generate Asymmetric Centers
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Asymmetric Center is Generated Racemic Mixture
Formed
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Asymmetric Induction
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Preparation of (L)-Dopafor Treatment of
Parkinsons
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Relevance of Stereochemistry
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One-step synthesis
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a-(p-isobutylphenyl)propionic acid
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Model of Thalidomide
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How Sweet it is!
Sucralose is 600 times sweeter and does not get
metabolized.
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Sildenafil (Viagra) and Caffeine
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Radiosensitizer of Choice Until 2004