chemistry 2100
DESCRIPTION
Chemistry 2100. Lecture 8. Enantiomers. Enantiomers: Nonsuperposable mirror images. As an example of a molecule that exists as a pair of enantiomers, consider 2-butanol. Enantiomers. alanine . chiral. asymmetric. glycine . plane of symmetry. achiral. Enantiomers. - PowerPoint PPT PresentationTRANSCRIPT
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Chemistry 2100
Lecture 8
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Constitutional
IsomersStereoisomers ConformationalIsomers
GeometricIsomersEnantiomers Diastereomers
single bond rotation
chiral achiral
sameconnections
differentconnections
notmirrorimages
mirrorimages
Isomers
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EnantiomersEnantiomers:Enantiomers: Nonsuperposable mirror images.– As an example of a molecule that exists
as a pair of enantiomers, consider 2-butanol.
OHC
H3C CH2CH3H
HOC
CH3H
CH3CH2Original molecule Mirror image
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Enantiomers
Original molecule
OHC
H3C CH2CH3H
OHC
CH3H
CH3CH2
OHC
H3C HCH2CH3
Mirror image The mirror imagerotated by 180°
180° rotate by 180°about the
C-OH bond
OHC
H3C CH2CH3H
OHC
H3C HCH2CH3
The original molecule
The mirror imageturned by 180°
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chiral
asymmetric
glycine
NH2H
C
COOH
CH3H2 NH CH3
C
COOH
alanine
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plane of symmetry
achiral
NH2
HC
COOH
CH3H2 NH CH3
C
COOH
glycine
H H
glycine
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EnantiomersObjects that are nonsuperposable on their mirror images are chiralchiral (from the Greek: cheir, hand).– They show handedness.The most common cause of enantiomerism in organic molecules is the presence of a carbon with four different groups bonded to it.– A carbon with four different groups
bonded to it is called a stereocenterstereocenter.
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Drawing Enantiomers
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thalidomide
N
O
ON
O
O
H
*
(CH3)2CHCH2 CH COOH
CH3
ibuprofen
*
NH2
CH CH3CH2
amphetamine
CH3
Enantiomers matter!
*
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Properties of Enantiomers
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Optical activity
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plane-polarized light
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plane-polarized light
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plane-polarized light
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plane-polarized light
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plane-polarized light
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Fig. 15-6, p. 435
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(±) or (dl) optically inactive raceme
levorotatory (l) (–) rotation "left-hand isomer"dextrorotatory (d) (+) rotation "right-hand isomer"
Assigning Rotation
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Multiple Chiral CentersFor a molecule with nn stereocenters, the maximum number of possible stereoisomers is 22nn.– We have already verified that, for a molecule
with one stereocenter, 21 = 2 stereoisomers (one pair of enantiomers) are possible.
– For a molecule with two stereocenters, a maximum of 22 = 4 stereoisomers (two pair of enantiomers) are possible.
– For a molecule with three stereocenters, a maximum of 23 = 8 stereoisomers (four pairs of enantiomers) are possible, and so forth.
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2R,3S 2S,3R 2R,3R 2S,3S
C
C
CHO
CH2OH
OHH
HHO
L-threose
C
C
CHO
CH2OH
OH
OHH
H
D-erythrose DC B A
C
C
CHO
CH2OH
OH
H
H
HO
D-threose
C
C
CHO
CH2OH
H
H
HO
HO
L-erythrose
The Four Stereoisomers of a Simple sugar
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C
C
Fischer Projections
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CHO
CH2OH
OH
H
H
HO
D-threose
CHO
CH2OH
OH
OHH
H
D-erythrose
CHO
CH2OH
H
H
HO
HO
L-erythrose
CHO
CH2OH
OHH
HHO
L-threose
Threose and Erythrose, Fischer-ized
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W X Y Z
meso
H
HO HO
H
COOH
COOH
COOH
COOH
OH
OHH
H
COOH
COOH
OHH
HHO
COOH
COOH
OH
H
H
HO
Tartaric Acid
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meso
COOH
COOH H H
OH
OH
W X Y Z
COOH
COOH
OH
OHH
H
COOH
COOH
OHH
HHO
COOH
COOH
OH
H
H
HO
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COOH
COOH H H
OH
OH
meso
× W X Y Z
COOH
COOH
OH
OHH
H
COOH
COOH
OHH
HHO
COOH
COOH
OH
H
H
HO
Meso form
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**
sodium ammonium tartrate
O
OH
CHCNa O CH C
OH
O NH4
O
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**
sodium ammonium tartrate
O
OH
CHCNa O CH C
OH
O NH4
O
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Stereochemical Reactions
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CH3
H
C
O
COOH
H
CH3 C COOH
O[H] *
pyruvic acid lactic acid
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*pyruvic acid
lactic acid
CH3
H
C
O
COOH
H
CH3 C COOH
O[H]
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(–)
(+)
H COOH
HO
CCH3
H CH3
HO
CCOOH
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(–)
(+)
H COOH
HO
CCH3
H CH3
HO
CCOOH
HH
HH
HH
HH
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COOH
COCH3
(–)
(+)
H COOH
HO
CCH3
H CH3
HO
CCOOH
HH
HH
HH
HH
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COOH
COCH3
CH3CO
COOH
(–)
(+)
H COOH
HO
CCH3
H CH3
HO
CCOOH
HH
HH
HH
HH
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COOH
COCH3
CH3CO
COOH
(–)
(+)
H COOH
HO
CCH3
H CH3
HO
CCOOH
HH
HH
HH
HH
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COOH
COCH3
CH3CO
COOH
(–)
(+)
H CH3
HO
CCOOH
HH
HH
HH
HH
H COOH
HO
CCH3
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COOHCO
CH3
CH3CO
COOH
(–)
(+)
H CH3
HO
CCOOH
HH
HH
HH
HH
H COOH
HO
CCH3
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COOHCO
CH3
CH3CO
COOH
(–)
(+)
H CH3
HO
CCOOH
H COOH
HO
CCH3
HH
HH
HH
HH
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(+)
HCOOH
HO
CCH3
But, Biologically…
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NAD H (+)
HCOOH
HO
CCH3
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NAD H (+)
HCOOH
HO
CCH3
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NAD H
COOHO
CH3
(+)
HCOOH
HO
CCH3
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OCH3C
COOH
NAD H
COOHO
CH3
(+)
HCOOH
HO
CCH3
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OCH3C
COOH
NAD H
COOHO
CH3
(+)
HCOOH
HO
CCH3
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OCH3C
COOH
NAD H
COOHO
CH3
(+)
HCOOH
HO
CCH3
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H+
OCH3C
COOH
NAD H
COOHO
CH3
(+)
HCOOH
HO
CCH3
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H+
OCH3C
COOH
NAD H
COOHO
CH3
(+)
HCOOH
HO
CCH3
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Chirality of Biomolecules– Because interactions between molecules in living
systems take place in a chiral environment, a molecule and its enantiomer or one of its diastereomers elicit different physiological responses.
– As we have seen, (S)-ibuprofen is active as a pain and fever reliever, while its R enantiomer is inactive.
– The S enantiomer of naproxen is the active pain reliever, but its R enantiomer is a liver toxin!
HOOC
H3C H
HOOC
H3C H
OCH3(S)-Ibuprofen (S)-Naproxen