Stereochemistry

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Chapter 5 Stereochemistry The Arrangement of
Atoms in Space The Stereochemistry of Addition
Reactions
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Molecular Chirality Enantiomers
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Chirality

• A molecule is chiral if its two mirror image
  forms are not superimposable upon one another.
• A molecule is achiral if its two mirror image
  forms are superimposable.

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Bromochlorofluoromethane is chiral

• It cannot be superimposed point for point on its
  mirror image.

Cl
Br
H
F
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Bromochlorofluoromethane is chiral
Cl
Cl
Br
Br
H
H
F
F

• To show nonimsuperposability, rotate this model
  180 around a vertical axis.

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Enantiomers
Chirality nonsuperimposable mirror images
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Isomers
constitutional isomers
stereoisomers
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Isomers
constitutional isomers
stereoisomers
enantiomers
diastereomers
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Physical Properties of Enantiomers
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Properties of enantiomers

• Physical properties are the same melting
  point, boiling point, density, etc
• Some others are different properties that
  depend on the shape of molecule eg.
  biological-physiological and optical properties.
  

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Odor
CH3
CH3
O
O
H3C
H3C
CH2
CH2
()-Carvonespearmint oil
()-Carvonecaraway seed oil
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Chiral drugs

• Ibuprofen is chiral, but normally sold asa
  racemic mixture. The enantiomer belowis the one
  responsible for its analgesic and
  antiinflammatory properties.

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A Sedative or a Potent Teratogen?
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The chiral carbon atom

• a carbon atom with fourdifferent groups attached
  to it
• also called
• chiral center chiral carbonasymmetric center
• asymmetric carbonstereocenter
• stereogenic center

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Chirality and chiral carbons

• A molecule with a single stereogenic center is
  chiral.
• 2-Butanol is an example.

H
CH3
CH2CH3
OH
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Examples of molecules with 1 chiral carbon
a chiral alkane
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Examples of molecules with 1 chiral carbon
Linalool, a naturally occurring chiral alcohol
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Examples of molecules with 1 chiral carbon
1,2-Epoxypropane a chiral carbon can be part of
a ring

• attached to the chiral carbon are
• H
• CH3
• OCH2
• CH2O

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Examples of molecules with 1 chiral carbon
Limonene a chiral carbon can be part of a ring

• attached to thechiral carbon are
• H
• CH2CH2
• CH2CH
• C

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Examples of molecules with 1 chiral carbon
Chiral as a result of isotopic substitution
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A molecule with a single chiral carbonmust be
chiral.

• But, a molecule with two or more chiral carbons
  may be chiral or it may not.
• Well return to this when we consider molecules
• with more than one chiral carbon atom.