1. Chapter 7 Stereochemistry
7.1 Molecular Chirality and Enantiomers
Molecular Chirality and Enantiomers
Characteristic of enantiomers
Chiral molecules
Chirality
7.1.2 Molecular Symmetry and
Asymmetric Molecules
Symmetric elements
Achiral Molecules
7.1.3 Properties of Chiral Molecules:
Optical Activity
7.1.4 Representation and Nomenclature
of Chiral Molecules

2. A. Representation
Fischer projections
B. Naming enantiomers with one
stereocenter by R-S notational system
7.2 Chiral Molecules With Two
Stereocenters
7.2.1 Chiral Molecules With Two
Different Stereocenter
Diastereomers
7.2.2 Stereoisomers With Two Same
Meso-form
7.2.3 Resolution of Enantiomers

3. ? Molecular constitution Molecular Molecular configuration （构型）
Constitutional isomers: to have the same
Molecular formula.
The atoms are bonded in different order: C skeleton isomers;isomers of the functional group site;isomers of functional group: Ex. CH3CH2OH, CH3OCH3
Molecular
structure
Molecular configuration （构型）
Stereoisomers:
The same mole. constitution
The former
is unchang-
ed by rota-
tion of C-C
Single bond
The different spatial arrangement of
atoms or groups
Enantiomers
(对映异构体)
Configurational isomers
Cis-,
Trans
Diastereomers
(非对映异构体)
Molecular confor-
mation(构象) ?
Conformers:
The same configuration
The different spatial arrangement of
atoms or groups by rotation of C-C single
bond

4. 7.1 Molecular Chirality[手(征)性] and Enantiomers
P183
Molecular Chirality and Enantiomers
A tetrahedron C is bonded to four different
groups, it’s not superposable on its
mirror image
Ex. Bromochlorofluoromethane:

6. Characteristic of enantiomers The same mole. constitution.
2. The relationship of enantiomers:
object and mirror image
3. Nonsuperposable
4. The same physical properties,
the similar chemical properties.
Chiral molecules:
with its enantiomer
Chirality:
Mole. isn’t superposable with
their mirror image

7. Chiral center: the carbon with 4 different groups. Ex.2-butanol: C2
(-)-Lactic acid
(乳酸) 1 2 3 4 5 6 *
An isotope *
Limonene
(柠檬油精)
1,2-Epoxypropane
(1,2-环氧丙烷)
Stereocenter or stereogenic center,
asymmetric center.
The molecule that contains one chiral
center have a pair of enantiomers

9. Achiral center: a C atom is attached by 2 or more same groups.
The molecule is achiral and is superposable
with its mirror image.
Achiral molecule(非手性分子).

10. 7.1.2 Molecular Symmetry and Asymmetric Molecules
P185,6.2
Symmetric elements:
A. A plane of symmetry(对称面)(σ)
A plane bisects a molecule so that
one half of molecule is the mirror image
of the other half.
Ex. 2-Chloropropane

11. 2. All atomes in a molecule are on a plane.
Ex. (E)-1,2-Dichloroethene

12. b. Center of symmetry(i)
If any straight line passes a atom and molecular
center, the same atom or group is encountered
on the site at equal distance but in the opposite
direction.
Ex.trans-2,4-dichloro-1,3-difluorocyclo-
butane

13. 7.1.3 Properties of Chiral Molecules: Optical Activity (旋光活性 or 光学活性)
Any molecule with a plane of symmetry
or a center of symmetry-Achiral molecule
A symmetric molecule.
Any chiral molecule is asymmetric one.
Nonsuperposable with its mirror image and
have a enantiomer.
7.1.3 Properties of Chiral Molecules:
Optical Activity (旋光活性 or 光学活性)
Optical activity:
When a beam of plane-polarized light
(平面偏振光)
pass through an enatiomer, the planar
polarization rotates.

14. Separate enantiomers rotate the plane of
plane-polarized light equal amounts and in
opposite direction.
Optically compounds
One enatiomer Levo-(左旋-) anticlockwise(-)
Other enantiomer Dextro- (右旋) clockwise(+)
(-)-2-Butanol, (+)-2-Butanol

15. The mixtures that contain equal amounts of
enantiomers are Racemic(外消旋).
(±)-2-Butanol
Polarimeter(旋光仪):
To measure the effect of plane-polarized
light on optically active compounds
Light source Polarizer Sample tube Analyzer
(起偏器) (检偏器)
Specific rotation
(比旋光度)
α: The observed rotation,
c: The concentration of the sample
(g/mL)
l: The length of the sample tube(dm)
λ:wavelength(D,589nm) Na
[α] λ = α cl

16. Percent enantiomeric excess
(-)-2-Butanol
(+)-2-Butanol
Ex.
Specific rotation:
+6.76°
+6.76° ee =
+13.5°
×100
50%
[α]D = °
[α]D = °
Optical purity(光学纯度):
50% pure
(+)- 2-butanol + 50%
(±)- 2-butanol
Percent enantiomeric excess
(对映体过量百分数)
ee =
Moles of one
enantiomer
Moles of both enantiomers -
moles of other
enatiomer
× 100 =
Observed specific rotation
Specific rotation of pure enantiomer

17. Jean Baptiste Biot
was born in Paris,
France, and was
educated there at the
École poly-technique.
His work on determining
the optical rotation of
naturally occuring
molecules included an
experiment on turpentine.
Jean Baptiste Biot
French Physicist
b. 1774
d. 1862

18. 7.1.4 Representation and Nomenclature of Chiral Molecules
A. Representation:
1. Wedge and dash drawing(伞式):
(+)-Lactic acid
(+)-乳酸)
(-)-Lactic acid
(-)-乳酸)
(+)-2-Butanol
2. Fischer projections
Ch.P113(二)
The rule for drawing:
Representation by
The longest carbon chain is on vertical
position.
The lowest numbered carbon is at the top.

19. Ex. The intersection of vertical and horizontal lines: chiral C atom.
Vertical line represents the bond that project
behind the plane of the paper;
Horizontal line represents the bond that project
out of the plane of the paper.
Ex.
(-)-2-Butanol
(南) P178

20. University Berlin, Germany
Generally considered the greatest
organic chemist of his time,
Fischer received the 1902 Nobel
Prize in Chemistry for his work
on carbohydrates and purines.
His discovery that phenylhydrazine
reacts with carbohydrates to form
osazones enabled him to elucidate
the stereochemistry of sugars.
First to synthesize adenine and
guanine, he made the first synthetic
nucleotides. Among many other
contributions was his work on
protein structure and synthesis,
the "lock-and-key" model for enzyme
reactions, structure of triarylmethane
dyes, and the design of
laboratory hoods and safety
equipment.
Hermann Emil Fischer
Germany Berlin
University Berlin, Germany
b d. 1919

21. Characteristics of Fischer projection
One group is fixed, the other three
groups are rotated in turn, the
configuration is not changed.

22. To rotate the projection to 90°, on the
plane of the paper, the other enatiomer
was got:
(+)-2-Bromobutane
(-)- 2-Bromobutane
Turn 90°
(-)-

23. To exchange any two groups, the configuration was changed, the other
enantiomer was got.
(-)-2-Bromobutane
(+)-
(-)-
(+)-
(+)-
(+)-

24. B. Naming enantiomers with one stereocenter by R-S notational system
P193, 6.6
Designation of absolute configuration
Rank the substituents according to
Cahn-Ingold-Prelog rule(序列规则).
(-)-2-Butanol
2. Orient the molecule so that the lowest
ranked substituent points away from you.
CH3 Et H OH

25. 7.2 Chiral Molecules With Two Stereocenter
3. Draw the tree highest ranked substituent
from the highest one to lowest one.
The direction:
Clockwise: ( R )-
Anticlockwise: ( S )-
P194
(-)-Lactic acid HO H
CH3 Et
(R)-2-Butanol
7.2 Chiral Molecules With Two
Stereocenter
P196, 6.7
7.2.1 Chiral Molecules With Two
Different Stereocenter
The four stereoisomers of
2,3-dihydroxybutanoic acid

26. (R)-甘油醛
(S)-甘油醛

27. 2,3-Dihydroxybutanoic acid*
(2R,3R)-
(2S,3S)-
(2R,3S)-
(2S,3R)-
(1) (2) (3) (4)
2,3-Dihydroxybutanoic acid
(2,3-二羟基丁酸)
Diastereomers:
(非对映异构体)
Normally n stereocenters
2n stereoisomers
Relationships of stereoisomers:
(3)
(1)
(2)
Enantiomers:
(1)
(2)
(3)
(4)
(4)

28. The relationship between diastereomers
is not related as an object and its mirror
imige.
Nomenclature for diastereomers:
Base on Fischer projection:
The same groups are on the same sides
of C chain: erythro-( 赤藓式)-
The same groups are on the opposite sides
of C chain: threo-( 苏藓式)-
erythro-
(赤型)-
(2R,3R)-

30. 7.2.2 Stereoisomers With Two Same Stereocenters
threo-
(苏型)-
(2S,3R)-
7.2.2 Stereoisomers With Two Same
Stereocenters
The meso form is achiral Mole.
Ex. Tartaric acid(酒石酸) * * * *
Diastereomer:
(7)
(5)
(6)
(2R,3S)-
meso form
(内消旋体)
(2R,3R)-
(2S,3S)-
erythro-
(5) (6) (7) (8)

32. Sodium ammonium tartrate
How about ?
Is it a chiral molecule or not, Why?
How about its trans-isomer? What
configuration are stereocenters in it?
7.2.3 Resolution of Enantiomers
（对映体的拆分）
Pasteur:
Recrystallization
(重结晶)
Two kind crystals
are mirror image
Sodium ammonium tartrate
(酒石酸铵钠)

33. Louis Pasteur 1822-1895 The scientific contributions of
Pasteur were among the most
valuable in the history of science,
and he is claimed equally
by chemistry and microbiology.
Best known to chemists for his
work on the tartaric acids,
he recognized the structural
relationships (now called chirality)
responsible for optical isomerism,
and that microorganisms can
distinguish between enantiomers.
Pasteur also showed that micro-
organisms cause fermentation and
various diseases, and he developed
methods for "pasteurization" and
for vaccination against anthrax
and rabies. His work saved the wine,
beer, and silkworm industries
for France.
Louis Pasteur

34. Resolution of racemic lactic acid
(R) salt
(S) salt
CH3NH2
Enan-
tiomer
Mirror
(R)
(S)
An R,R-salt
An S,R-salt
Dia-
stereo
mer

35. Problems to Chapter 6 P212 6.25 (a),(d) 6.26 6.30 6.33 (a)~(c) 6.34
6.35
6.36
6.37
6.39
6.40
6.46(b)
6.49
6.50
6.52 Ribitol(核糖醇)
6.57, 6.58

36. Additional Problems:
Which of the following pairs of Fischer
projection represent the same enantiomer,
and which represent different enantiomers？
2. Assign R or S conformation to the
following Fischer projections:

37. 1,4-dimethylcyclohexane?
3. Draw Fischer projections that fit the
following descriptions:
(a) The R enantiomer of alanine(丙氨酸) ,
CH3CH(NH2)COOH
(d) The S enantiomer of 3-methylhexane
4. Suppose that racemic lactic acid reacts with
(S)-2-butanol(丁醇) to form an ester. What
stereochemistry dose the product(s) have?
What is the relationship of one product to
another?
*5. Draw both and trans-1,4-dimethyl-
cyclohexane in their most chair conformation.
(a) How many stereoisomers are there of cis-
1,4-dimethylcyclohexane?
(b) Are any of the structure chiral?
(c) What are the stereochemistry relationships
among the various stereoisomers of
1,4-dimethylcyclohexane