大二有机第五章

1、 Chapter Five StereochemistryClassification of Isomers Chirality (手性) and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic MixtureEnantiomers (对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers With No

2、 Chiral CenterIntroductionA flow diagram summarizing the different kinds of isomers 构造异构体 立体异构体 对映异构体 非对映异构体 构象异构体 顺反异构体 Chapter Five StereochemistryClassification of Isomers Chirality and Chiral MoleculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Race

3、mic MixtureEnantiomers (对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers With No Chiral CenterThe Disaster of Thalidomide “反应停”灾难thalidomideChirality and Chiral Molecules？沙利度胺（Thalidomide) 又名反应停 The thalidomide is a chiral molecule (手性分子) and has two enantiomers (对

4、映异构体) : R and S configurations, while R configuration is used to reduce pregnant reactions, S configuration is deforming (致残).Chirality and Chiral Molecules左手与其镜像不能完全重合1. Chirality (手性)Chirality and Chiral Molecules Things that are not superimposable (重合的) on their mirror images (镜像) are said to be

5、chiral (手性的).Chirality and Chiral Molecules？Chirality and Chiral Molecules2. Chiral Molecules (手性分子)Louis Pasteur (18221895)1848 年COONaOHHCOONH4HOHCOONaHOHCOONH4OHHChiral Carbon: A carbon atom bonded to four different groups. C*Rotate 180 Rotate 180 Chiral Molecule :Molecules that are not superimpos

6、able with their mirror images. Chirality and 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.*Inden

7、tify the chiral carbons in the following molecules. *ReviewChirality 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 面) or symmetri

8、c center (对称中心) . 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)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnanti

9、omers With No Chiral Center乳酸 ( Lactic acid )*EnantiomersEnantiomersEnantiomers Mirror-image molecules that are not superimposable are called enantiomers (对映异构体).All chiral molecules exist enantiomers-凡手性分子都存在对映异构体 Chapter Five StereochemistryClassification of Isomers Chirality and Chiral MoleculesE

10、nantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic MixtureEnantiomers (对映异构体)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers With No Chiral CenterProperties of Enantiomers: Optical ActivityLight sourceUnpolarized light 非偏振

11、光Polarizer 起偏镜Polarized light 偏振光Sample tube containing some organic molecule Analyzer 检偏镜Observer1. Optical Activity (光学活性) Those compounds that can rotate the plane of polarization are said to be optically active.Polarimeter 旋光仪Properties of Enantiomers: Optical ActivityLevorotatory (左旋体)：rotate p

12、olarized light to be left. “一”Dextrorotatory (右旋体)：rotate polarized light to be right. 2. Specific Rotation (比旋光度) The amount of rotation (旋光度) depends on both sample concentration (样品溶度) and sample pathlength (样品管的长度).“+” Chapter Five StereochemistryClassification of Isomers Chirality and Chiral Mo

13、leculesEnantiomers with One Chiral CenterProperties of Enantiomers: Optical ActivityResolution of Racemic MixtureEnantiomers (对映异构)Enantiomers with Two Chiral CentersStereoisomer of Cyclic CompoundsEnantiomers With No Chiral Center1. Enantiomers and Racemate (外消旋体)m.p. = 18Racemate(外消旋体)：A mixture o

14、f equal Levorotatory (左旋体) and Dextrorotatory (右旋体).Racemate is not optical activeEnantiomers with One Chiral Center(1). Wedge drawing(楔形式):(2). Fischer projections ( Fischer 投影式) In 1891, Emil Fischer (1852-1919, 1902 Nobel Prize winner) suggested a method based on the projection of a tetrahedral c

15、arbon 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)；b. The main chain(主碳链) is on the vertical lines.c. The cross point (交叉点) represents a chiral carbon.d.

16、The horizontal lines(水平线) represent bonds coming out of the page(横出)；e. The vertical lines represent bonds going into the page (竖进) .Enantiomers with One Chiral Center123111. Convert the following wedge drawing representation of 2- Chlorobutane into a Fischer projection:Enantiomers with One Chiral C

17、enterExercise:*The properties of Fischer projection:a. A Fischer projection can be rotated on the page by 180o, and the configuration retains (构型保持).b. A Fischer projection can have one group held steady while the other three rotate in either a clockwise or a counterclockwise direction，and the confi

18、guration retains 。Enantiomers with One Chiral Center固定一个基团，依次轮转其它三个基团纸面上旋转 180c. Any two groups exchange their positions, the configuration changes (构型变) and gets its enantiomers (得到对映体). Enantiomers with One Chiral Center任意两个基团互换构型变d. A Fischer projection rotates on the page by 90 or 270o, the conf

19、iguration changes and gets its enantiomers。Roate 90Enantiomers with One Chiral Center纸面上旋转 90 或270构型变Exercise:1. Which of the following compounds are same with: Enantiomers with One Chiral Center A verbal method for indicating the three-dimensional arrangement of atoms, or configuration (构型), at a c

20、hirality center is necessary.3. RS Nomenclature system:Step1: Assign priorities the four atoms or groups attached to the chiral carbon center.Enantiomers with One Chiral Center1234Step2: Orientate the molecule so that the group of lowest priority (4) is pointing directly back, away from us.Enantiomers with One Chiral CenterStep3: Draw a curved arrow from the highest to second to third- priority groups (12 3), If the arrow is clockwise (顺时针), t