Stereochemistry of electrophilic addition reactions of alkenes
#Separating
enantiomers
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Prepared by Yang R. L.
Stereochemistry of electrophilic addition reactions of alkenes
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1
#Chiral,
cheir & chiron
• 3-氯戊烷 • 3-氯丁烯
Question-2
Point out the chiral carbon in the molecules below
• 2-甲基-3-氯戊烷
t= []D
lc
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Plane polarized light (平面偏振光 )
Beam of light
Enantiotropy* (对映)
Normal light
Polarizer
Plane-polarized light
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Fisher projection* COOH COOH H C OH H OH chiral CH3 CH3
carbon
横前 竖后
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Prepared by Yang R. L.
2
Fisher projection*
4
Nomenclature: R, S
4
The centaur Chiron taught young Askelpios the art of healing
• 3-甲基环己烯
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Prepared by Yang R. L.
Chiral* molecules (手性分子)
True or false
Chiral molecules that do not possess chirality center
(1R,2R)-1,2-dibromo cyclopropane
(1S,2S)-1,2-dibromo cyclopropane
meso-1,2-dibromo cyclopropane
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Thalidomide (沙利度胺)
S
R
Newborn male infant showing typically malformed limbs caused by thalidomide ingested by the mother during early pregnancy
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The S-image of limonene is present in the cones of fir trees and has a turpentinelike odor; the R-mirror image gives oranges their characteristic fragrance
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Optical activity* (旋光性)
Rotation
Enantiotropy* (对映)
ized light
Sample cell
Analyzer
与镜像不能重合的分子具有旋光性
3 2
1
3 1
2
S-lactic acid
R-lactic acid
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Prepared by Yang R. L.
Nomenclature: D, L
CHO OH H OH * OH CH2OH
R
Nomenclature: R, S
R
D-甘油醛
H HO H H
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Caution
D, L and R, S has nothing to do with direction of light rotation! Just rules of nomenclature
Propanolol (心得安)
R
S
男性避孕
治心脏病
D-(-)-Lactic acid
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Chirality
Optical activity* (旋光性)
• Clockwise, (+) or (d) • Counterclockwise, (-) or (l)
[] D t l c specific rotation wavelength (589nm) temperature optical rotation in degress length of sample container (dm) concerntration g/ml
S
S R
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R
S
D-葡萄糖
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Nomenclature: D, L
R, S- in Fisher projection
S L-甘油醛 L-丙氨酸
changes into
R
R
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D-(+)-Alamine
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Enantiomers in nature
Racemic mixtures (外消旋体)
• Equal quantities of d- and l- enantiomers • Notation: (d,l) or () • No optical activity • The mixture may have different b.p. & m.p. from the enantiomers
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Molecules with several stereocentres
• Molecules with n stereocenters can have 2n stereoisomers • Morphine 25 = 32 • Nature makes only 1
Epimers (差向异构体)
Chiral molecules that do not possess chirality center
Ephedrine (麻黄碱)
Pseudoephedrine (伪麻黄碱)
Hexahelicene Top view
Side view
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(+) (-) Meso ()
168-170 168-170 146-168 206
+12 -12 0 0
1.7598 1.7598 1.6660 1.7880
139.0 139.0 125.0 20.6
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Prepared by Yang R. L.
Molecules with two stereocentres
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Isomers
Isomers
＃ Stereochemistry
of electrophilic addition reactions of alkenes
(赤式)
Constitutional isomers Differ in order of attachment Stereoisomers Differ in spatial orientation
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Physical properties of tartaric acid
Stereoisomer m.p. (C) []D Density (g/cm3) Solubility at 20C (g/100ml H2O)
Chiral molecules that do not possess chirality center
Question-3
• 含有手性碳的分子是手性分子 • 含有一个手性碳的分子一定是手性分子 • 不能与其镜像重合的分子是手性分子 • 手性分子与其镜像互为对映体
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Prepared by Yang R. L.
Question-1
Indicate whether there is plane of symmetry in the molecules below
changes back into
S
3
R, S- in Fisher projection
Biological discrimination
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Prepared by Yang R. L.
Properties of enantiomers
• Same boiling point, melting point & density • Same refractive index (折射率) • Different direction of rotation in polarimeter • Different interaction with other chiral molecules (enzymes)