chapter 5 stereochemistry: chiral molecules - 厦门大学化...
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Chapter 5 Stereochemistry: Chiral Molecules
立体化学: 手性分子
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.1 Isomerism: Constitutional Isomers and Stereoisomers
异构现象：构造异构和立体异构
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
IsomersIsomers are different compounds that have the same molecular formula.
Constitutional isomers are isomers that differ because their atoms are connected in a different order.Stereoisomers differ only in arrangement of their atoms in space.Stereoisomers are not constitutional isomers.
Enantiomers are stereoisomers whose molecules are nonsuperposable mirror images of each other.Diastereomer are stereoisomers whose molecules are not mirror images of each other.
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.2 Enantiomers and Chiral molecules
对映异构和手性分子
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
Chiral: An object that if it is not superimposable on its mirror image.Chiral molecules: A chiral molecule is defined as one that is not identical with its mirror image.Achiral: Objects that are superposable on their images are achiral.
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
EnantiomersMolecules that are nonidentical with their mirror images are a special kind of stereoisomers called enantiomers.
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
A pair of enantiomers is always possible for molecules that contain one tetrahedral atom with four different groups attached to it.Interchanging any two groups at the tetrahedral atom that bears four different groups converts one enantiomer into the other.Stereocenter — an atom bearing groups of such nature that an interchange of any two groups will produce a stereoisomer.
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.3 The Biological Importance of Chirality
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
HOO
H
H
HO
H
OHOHH
H
OH
(+)-D-葡萄糖
CO2HNH2H
CH2CONH2
D-天门冬酰胺D-AsparagineD-Glucose
D-form—sweetL-form—bitter
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
NO2
CHOHHOCH2CHNHCOCHCl2
氯霉素
PhC
Ph
COCH2CH3
CH2CHN(CH3)2
CH3
Methadone美散痛
*
*
*
Chloromycetin
(+)-Chloromycentineffectless
(+)-Methadoneeffectless
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.4 Historical Origin of Stereochemistry
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
石英晶体
Crystal quartzleft-handed quartzright-handed quartz
1849 Louis Pasteur — sodium ammonium tartrate separated as
left-handed crystalsright-handed crystals
Mixed right and left(1:1)— optically inactive
CO2NaCH OHCHO HCO2NH4
Sodium ammonium tartrate酒石酸钠铵
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.5 Tests for Chirality: Planes of Symmetry
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
Plane of Symmetry (对称面)
Plane of symmetry (mirror plane)— an imaginary plane that bisects a molecule in such a way that two halves of the molecule are mirror images of each other.All molecules with a plane of symmetry are achiral.
A plane of symmetryA plane of symmetry
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
Center of symmetry (对称中心)
Cl
Cl
FF
A center of symmetryA center of symmetry
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
Alternating axes of symmetry(交替对称轴)
Cl
Cl
FF 180
F
F
ClCl
F
F
Cl
ClA alternating axes of symmetryA alternating axes of symmetry
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.6 Nomenclature of Enantiomers: The (R-S) System
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
Sequence rules (by Cahn–Ingold–Prelog)Configuration — the spatial arrangement of substituents at a chiral centerEach of the four groups attached to the stereocenter is assigned a priority or preference a, b, c, and d. Priority is first assigned on the basis of the sequence rules.
H C
CH3
CO2HOH
(-)-Lactic acid
ab
cd
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
da b
c
Sequence rules: a >b >c >d (lowest)
(R)
a →b →c clockwise — (R)a →b →c counterclockwise — (S)
a
bc
da →b →c clockwise — (R)
(R)-2-Hydroxylpropanoic acid(R)-2-羟基丙酸
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
H C
CH3
CO2HOH
HC
CH3
CO2HHO
R S
(R)-2-Hydroxylpropanoic acid(R)-2-羟基丙酸
(S)-2-Hydroxylpropanoic acid(S)-2-羟基丙酸
H C
CH2CH3
CH3Cl
HC
CH3CH2
CH3Cl
RS
(S)-2-Chlorobutane(S)-2-氯丁烷
(R)-2-Chlorobutane(R)-2-氯丁烷
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.7 Properties of Enantiomers: Optical Activity
对映体的性质：光学活性
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.7A Plane-Polarized Light
Optical activity is the ability of a chiral substance to rotate the plane of plane-polarized light and its measured using an instrument called a polarimeter.
振动面
偏振面
Plane-polarized lightPlane-polarized light
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.7B The Polarimeter (旋光仪)
(+) dextrorotaory 右旋(-) levorotatory 左旋
α
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
5.7C Specific Rotation (比旋光度)
α Dt = l C
α
Where [α] = the specific rotation
α = the observed rotation
c = the concentration of the solution in grams per milliliterof solution (or density in mL-1 for neat liquids)
l = the length of the tube in decimeters
ORGANIC CHEMISTRY
Department of Chemistry, Xiamen University
Chapter 5
No obvious correlation exists between the configuration of enantiomers and the direction [ (+) or (-) ] in which they rotate plane-polarized light.No obvious correlation exists between the the (R) and (S) designation and the direction of rotation of plane-polarized light.
C
CH2CH3
CH3
HHO C
CH2CH3
CH3
OHHC
CH2CH3
CH3
HHOCH2 C
CH2CH3
CH3
CH2OHH
(R)-2-Butanol (S)-2-Butanol
[α]D25 = −13.52 [α]D
25 = +13.52 [α]D25 = −5.756[α]D
25 = +5.756