Stereochemistry

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Stereochemistry
The Arrangments of Atoms in space The
Stereochemistry of Addition Reactions
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Configurational Isomers Isomers
With One Chirality Centers
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Nomenclature of Enantiomers-The R-S System

• Orient the molecule so that the group
• with lowest priority (4) is directed away
• from you.
• Then draw an imaginary arrow from the
• group (or atom) with highest priority (1)
• to the group (or atom) with the next
• highest priority (2)

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Nomenclature of Enantiomers-The R-S System

• Orient the molecule so that the group
• with lowest priority (4) is directed away
• from you.
• Then draw an imaginary arrow from the
• group (or atom) with highest priority (1)
• to the group (or atom) with the next
• highest priority (2)

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Nomenclature of Enantiomers-The R-S System
2
CH2CH3
CH2CH3
switch CH3 and H
c
3
C
1
CH3
H
HO
HO
H
CH3
4
This compound has the R configuration which
means that the compound before the Switch has the
S configuration
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Nomenclature of Enantiomers-The R-S System
For compounds containing multiple bonds one other
rule is needed - Priorties assigned as if both
atoms were duplicated or triplicated, i.e
C Y as if it were - C - Y
(Y) (C)
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Nomenclature of Enantiomers-The R-S System
(Y) (C )
- C Y as if it were - C Y
(Y) (C )
Thus, the vinyl group, -CH CH2, is of higher
priority than the isopropyl group, -CH(CH3)2
-CH CH2 is treated as if C C
H
H H
(C) (C)
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Draw the R and S configuration for each of the
following compounds a. 2-bromopentane b.
2-chloro-2-propylheptane
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Dextrorotatory ()
levorotatory (-)
C g/ml
Racemic
-
l/dm
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Problem
The observed rotation of 2.0 g of a compound in
10 mL of solution in polarimeter tube 25 cm long
is 134o. What is the specific rotation of the
compound.
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Optical Rotation
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Optical Purity
Observed specific Rotation
Optical Purity
specific rotation of the pure isomer
For example, if a sample of 2-bromobutane has an
observed specific rotation of 9.2o, its optical
purity is 0.40. In other words, it is 40
optically pure.
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Molecules with More than One Stereocenter
similar groups are similar
groups are on the same side
on the opposite side
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Meso Compounds
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Meso Compounds
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Reactions of Compounds That Contain A Chirality
Centers
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