有机化学：第五章Stereochemistry

1、 Chapter Five StereochemistryClassification of Isomers Chirality (手性手性) and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic MixtureEnantiomers (对映异构对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers W

2、ith No Chiral CenterIntroductionA flow diagram summarizing the different kinds of isomers 构造异构体构造异构体 立体异构体立体异构体 对映异构体对映异构体 非对映异构体非对映异构体 构象异构体构象异构体 顺反异构体顺反异构体IsomersConstitutional isomers Stereo isomers Enantiomers(mirror-imagine) Diastereomers(non-mirror-imagine) Conformationdiastereomers Cis-transd

3、iastereomers Chapter Five StereochemistryClassification of Isomers Chirality and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic MixtureEnantiomers (对映异构对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiom

4、ers With No Chiral CenterThe Disaster of Thalidomide -thalidomideChirality and Chiral Molecules？NOONHHOONHOONOOH沙利度胺沙利度胺（Thalidomide) 又名反应停又名反应停 The thalidomide is a chiral molecule (手性分子手性分子) and has two enantiomers (对映异构体对映异构体) : R and S configurations, while R configuration is used to reduce preg

5、nant reactions, S configuration is deforming (致残致残).Chirality and Chiral Molecules左手与其镜像不能完全重合左手与其镜像不能完全重合1. Chirality (手性手性)Chirality and Chiral Molecules Things that are not superimposable (重合的重合的) on their mirror images (镜像镜像) are said to be chiral (手性的手性的).Chirality and Chiral MoleculesChirality

6、 and Chiral Molecules2. Chiral Molecules (手性分子手性分子)Louis Pasteur (1822(18221895)1895)COONaOHHCOONH4HOHCOONaHOHCOONH4OHHChiral Carbon: A carbon atom bonded to four different groups. C*Rotate 180 Rotate 180 Chiral Molecule : :Molecules that are not superimposable with their mirror images. Chirality an

7、d Chiral MoleculesChiral CenterReviewChiral Carbon: A carbon atom bonded to four different groups. C*Chiral Molecule: Molecules that are not superimposable with their mirror images. Chirality: Things that are not superimposable on their mirror images.*Indentify the chiral carbons in the following mo

8、lecules. *OCH3CCH2CH3CH3ReviewNOONOOHChirality and Chiral MoleculesHow can we predict whether a given molecule is chiral or achiral? a. If a molecule only has one chiral carbon, it must be chiral. b. A molecule is not chiral if it contains a plane of symmetry (对称对称 面面) or symmetric center (对称中心对称中心)

9、 .CH3HHHCH3HHCIHHCIH Chapter Five StereochemistryClassification of Isomers Chirality and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic Mixture Enantiomers (对映异构对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic Compound

10、sEnantiomers With No Chiral Center乳酸乳酸 ( Lactic acid )CH3OHHCOOHCCOOHHOHCH3C-*CCH3COOHOHHEnantiomersEnantiomersEnantiomers- Mirror-image molecules that are not superimposable are called enantiomers (对映异构体对映异构体).All chiral molecules exist enantiomers-凡手性分子都存在对映异构体凡手性分子都存在对映异构体COOHH3COHHCOOHCH3HOH Cha

11、pter Five StereochemistryClassification of Isomers Chirality and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic MixtureEnantiomers (对映异构体对映异构体)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers With No Ch

12、iral CenterProperties of Enantiomers: Optical ActivityLight sourceUnpolarized light 非偏振光非偏振光Polarizer 起偏镜起偏镜Polarized light 偏振光偏振光Sample tube containing some organic molecule Analyzer 检偏镜检偏镜Observer1. Optical Activity (光学活性光学活性) Those compounds that can rotate the plane of polarization are said to b

13、e optically active.Polarimeter 旋光仪旋光仪- roration 旋光度Properties of Enantiomers: Optical ActivityLevorotatory (左旋体左旋体)：rotate polarized light to be left. “一一”Dextrorotatory (右旋体右旋体)：rotate polarized light to be right. 2. Specific Rotation (比旋光度比旋光度) The amount of rotation (旋光度旋光度) depends on both sampl

14、e concentration (样品溶度样品溶度) and sample pathlength (样品管的长度样品管的长度).CConcentration, g/mlLPathlength, dm =LC- Observed roration(degrees)D=+ 52.5 （水）020“+” Chapter Five StereochemistryClassification of Isomers Chirality and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optic

15、al ActivityResolution of Racemic MixtureEnantiomers (对映异构对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers With No Chiral CenterCOOHH3CHOHCOOHCH3HHO(-)-lactic acidm.p. = 5315D15D= + 2.6= -2.6m.p. = 53(+)-lactic acid-1. Enantiomers and Racemate (外消旋体外消旋体)CH3CHCOOHOHm

16、.p. = 18+Lactic acidRacemate(外消旋体外消旋体)：A mixture of equal Levorotatory (左旋体左旋体) and Dextrorotatory (右旋体右旋体).Racemate is not optical activeEnantiomers with One Chiral Center+(1). Wedge drawing( (楔形式楔形式):):COOHCH3HHOCOOHH3CHOH(2). Fischer projections ( Fischer 投影式投影式) In 1891, Emil Fischer (1852-1919,

17、 1902 Nobel Prize winner) suggested a method based on the projection of a tetrahedral carbon atom onto a flat surface.Enantiomers with One Chiral Center2. Representation of Chiral Molecules a. A tetrahedral carbon atom is represented in a Fischer projection by two crossed lines(交叉线交叉线)；b. The main c

18、hain(主碳链主碳链) is on the vertical lines.c. The cross point (交叉点交叉点) represents a chiral carbon.d. The horizontal lines(水平线水平线) represent bonds coming out of the page(横出横出)；e. The vertical lines represent bonds going into the page (竖进竖进) .CH3CHCOOHOHCOOHCH3OHHCOOHCH3HHOEnantiomers with One Chiral Cente

19、r123111. Convert the following wedge drawing representation of 2- Chlorobutane into a Fischer projection:CHClCH3CH2CH3Enantiomers with One Chiral CenterExercise:C2H5CH3ClHCH3CHCH2CH3Cl*The properties of Fischer projection:a. A Fischer projection can be rotated on the page by 180o, and the configurat

20、ion retains (构型保持构型保持).CH3CH2CH3BrHCH2CH3CH3HBrb. A Fischer projection can have one group held steady while the other three rotate in either a clockwise or a counterclockwise direction，and the configuration retains 。CH3CH2CH3BrHCH3BrHCH3CH2Enantiomers with One Chiral Center固定一个基团，依次固定一个基团，依次轮转其它三个基团

21、轮转其它三个基团纸面上旋转纸面上旋转 180c. Any two groups exchange their positions, the configuration changes (构型变构型变) and gets its enantiomers (得到对映体得到对映体). BrHCH2CH3CH3CH3CH2CH3BrHCH3CH2CH3BrHEnantiomers with One Chiral Center任意两个基团互换任意两个基团互换构型变构型变d. A Fischer projection rotates on the page by 90 or 270o, the confi

22、guration changes and gets its enantiomers。CH3HBrCH2CH3Roate 90CH3CH2CH3BrHCH3CH2CH3BrHEnantiomers with One Chiral Center纸面上旋转纸面上旋转 90 或或270构型变构型变Exercise:1. Which of the following compounds are same with: COOHHOHCH3CH3HOHCOOHOHHCOOHCH3CH3HOOCOHHCOOHHOCH3HEnantiomers with One Chiral Center A verbal m

23、ethod for indicating the three-dimensional arrangement of atoms, or configuration (构型构型), at a chirality center is necessary.3. RS Nomenclature system:Step1: Assign priorities the four atoms or groups attached to the chiral carbon center.CHOHCOOHCH3Enantiomers with One Chiral Center1234Step2: Orient

24、ate the molecule so that the group of lowest priority (4) is pointing directly back, away from us.CHOHCOOHCH3Enantiomers with One Chiral CenterCHOCOOHCH3HStep3: Draw a curved arrow from the highest to second to third- priority groups (12 3), If the arrow is clockwise (顺时针顺时针), the chirality center has R configuration. If the arrow is counterclockwise (逆时针逆时针), the chirality center has S configurationEnantiomers with One Chiral CenterRSCHOCOOHC