有机化学Chapter 7. Stereochemistry立体化学.

1、Chapter 7 Stereochemistry 7.1 Molecular Chirality and Enantiomers Characteristic of enantiomers Chiral molecules Chirality 7.2 Molecular Symmetry and Asymmetric Molecules Symmetric elements Achiral Molecules 7.3 Properties of Chiral Molecules: Optical Activity 7.4 Representation and Nomenclature of

2、Chiral Molecules A. Representation Fischer projections B. Naming enantiomers with one stereocenter by R-S notational system 7.5 Chiral Molecules With Two Stereocenters 7.5.1 Chiral Molecules With Two Different Stereocenter： Diastereomers 7.5.2 Stereoisomers With Two Same Stereocenters Meso-form 7.5.

3、3 Physical Properties of Stereoisomer 7.6 Resolution of Enantiomers Cis-, Trans Molecular structure Molecular constitution（分子构造）（分子构造） Constitutional isomers: to have the same Molecular formula. Molecular configuration （分子构型）（分子构型） Stereoisomers: The same mole. constitution The different spatial arr

4、angement of atoms or groups Enantiomers (对映异构体对映异构体) Diastereomers (非对映异构体非对映异构体) The former is unchang- ed by rota- tion of C-C Single bond Configurational isomers ? Molecular confor- mation(构象构象) Conformers: The same configuration The different spatial arrangement of atoms or groups by rotation of

5、 C-C single bond The atoms are bonded in different order: （1）C skeleton isomers; （2）Isomers of the functional group site; （3）Isomers of functional group: 7.1 Molecular Chirality 手手(征征)性性 and Enantiomers A tetrahedron C is bonded to four different groups, its not superposable on its mirror image Ex.

6、Bromochlorofluoromethane: turn 180 C H Cl Br F C Br H Cl F C Cl F Br H C CH3 H OH CH2CH3 C OH CH3 H H3CH2C Enantiomers Characteristic of enantiomers The same molecular constitution. 2. The relationship of enantiomers: object and mirror image 3. Nonsuperposable 4. The same physical properties, the si

7、milar chemical properties. Chiral molecules: with its enantiomer Chirality: Mole. isnt superposable with their mirror image Stereocenter or stereogenic center, asymmetric center. H2CC O H CH3 * 1,2-Epoxypropane (1,2-环氧丙烷环氧丙烷) CCH2 CH3 H CH3 1 2 3 4 5 6 Limonene (柠檬油精柠檬油精) * The molecule that contain

8、s one chiral center have a pair of enantiomers C D H Cl CH3 C D CH3 Cl H An isotope Chiral center: the carbon with 4 different groups. Ex.2-butanol: C2 C COOH CH3 H HO (-)-Lactic acid (乳酸乳酸) C H D CH3 Cl C D H CH3 Cl Achiral center: a C atom is attached by 2 or more same groups. C H Cl F H turn 180

9、turn 180 Achiral molecule(非手性分子非手性分子). C Cl H H F The molecule is achiral and is superposable with its mirror image. 7.2 Molecular Symmetry and Asymmetric Molecules Symmetric elements: A. A plane of symmetry(对称面对称面)() A plane bisects a molecule so that one half of molecule is the mirror image of the

10、 other half. P180,6.2 Ex. 2-Chloropropane 2. All atoms in a molecule are on a plane. Ex. (E)-1,2-Dichloroethene B. Center of symmetry(i)（对称点）（对称点） 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 directio

11、n. Ex.trans-2,4-dichloro-1,3-difluorocyclo- butane F F Cl Cl H H H H 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. 7.3 Properties of Chiral Molec

12、ules: Optical Activity (旋光活性旋光活性 or 光学活性光学活性) Optical activity: When a beam of plane-polarized light (平面偏振光平面偏振光) pass through an enantiomer, the planar polarization rotates. Polarimeter(旋光仪旋光仪): To measure the effect of plane-polarized light on optically active compounds Light source Polarizer Samp

13、le tube Analyzer Specific rotation (比旋光度比旋光度) : The observed rotation, c: The concentration of the sample (g/mL) l: The length of the sample tube(dm) :wavelength(D,589nm) Na t: temp. P184 t = c * l Separate enantiomers rotate the plane of plane-polarized light equal amounts and in opposite direction

14、. Optically compounds One enantiomer Levo-(左旋左旋-) anticlockwise(-) Other enantiomer Dextro- (右旋右旋) clockwise(+) (-)-2-Butanol, (+)-2-Butanol The mixtures that contain equal amounts of enantiomers are Racemic(外消旋外消旋). ()-2-Butanol Jean Baptiste Biot French Physicist b. 1774 d. 1862 Jean Baptiste Biot

15、 was born in Paris, France, and was educated there at the cole poly-technique. His work on determining the optical rotation of naturally occureing molecules included an experiment on turpentine. 7.4 Representation and Nomenclature of Chiral Molecules A. Representation: 1. Wedge and dash drawing(伞式伞式

16、): C H HO COOH CH3 C OH H HOOC CH3 (+)-Lactic acid (+)-乳酸乳酸) (-)-Lactic acid (-)-乳酸乳酸) 2. Fischer projections The rule for drawing Representation by The longest carbon chain is on vertical position （将最长的碳链置于垂直的位置上）（将最长的碳链置于垂直的位置上） The lowest numbered carbon is at the top. （将编号最小的碳原子置于顶端）（将编号最小的碳原子置于

17、顶端） The intersection of vertical and horizontal lines: chiral C atom. (垂直与水平的交叉点就是手性碳）垂直与水平的交叉点就是手性碳） Ex. C H HO CH3 CH2CH3 (-)-2-Butanol CH3 CH2CH3 HOH C CH3 CH2CH3 H HO Vertical line represents the bond that project behind the plane of the paper （垂直线两端表示在纸面下方的两个基团）（垂直线两端表示在纸面下方的两个基团）; Horizontal l

18、ine represents the bond that project out of the plane of the paper （水平线两端表示在纸面上方的两个基团）（水平线两端表示在纸面上方的两个基团）. R-(-)-2-Butanol Hermann Emil Fischer Germany Berlin University Berlin, Germany b. 1852 d. 1919 Generally considered the greatest organic chemist of his time, Fischer received the 1902 Nobel Pri

19、ze 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 contribu

20、tions 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. CH3 CH2CH3 BrH CH3 Br HCH3CH2 Characteristics of Fischer projection One group is fixed, the other three group

21、s are rotated in turn, the configuration is not changed. To exchange any two groups, the configuration was changed, the other enantiomer was got. CH3 CH2CH3 BrH CH2CH3 CH3 H Br (-)-2-Bromobutane(+)- Br CH3 CH2CH3 H (+)- turn 109.5 (-)- (+)- (+)- B. Naming enantiomers with one stereocenter by R-S not

22、ational system Designation of absolute configuration Rank the substituents according to Cahn-Ingold-Prelog rule(序列规则序列规则). 2. Orient the molecule so that the lowest ranked substituent points away from you. C CH3 CH2CH3 H HO (-)-2-Butanol OH CH2CH3CH3 H CH3 Et H OH 3. Draw the tree highest ranked sub

23、stituent from the highest one to lowest one. The direction: Clockwise: ( R )- Anticlockwise: ( S )- OH CH3CH2 CH3 CH3 HO CH2CH3 H (R)-2-Butanol P194HO H CH3 Et (-)-Lactic acid CH OH COOH CH3 C H H3C OH COOH 7.5 Chiral Molecules With Two Stereocenter 具有两个手性中心的对映异构具有两个手性中心的对映异构 7.5.1 Chiral Molecules

24、With Two Different Stereocenter 具有两个不同手性碳原子的对映异构具有两个不同手性碳原子的对映异构 The four stereoisomers of 2,3-dihydroxybutanoic acid COOH CH3 H H OH OH COOH CH3 HO HOH H COOH CH3 H H OH HO COOH CH3 H OH HO H (1) (2) (3) (4) * * * * * * * * (2R,3R)-(2S,3S)-(2R,3S)-(2S,3R)- 2,3-Dihydroxybutanoic acid (2,3-二羟基丁酸二羟基丁酸

25、) Normally n stereocenters 2n stereoisomers Relationships of stereoisomers: Enantiomers: (1)(2) (3)(4) Diastereomers: (非对映异构体非对映异构体) (1) (3) (4) (2) COOH H OH HO H COOH COOH COOH H H OH OH 7.5.2 Stereoisomers With Two Same Stereocenters Ex. Tartaric acid(酒石酸酒石酸) COOH H H OH HO COOH (2R,3R)- * * * *

26、* * COOH HO HOH H COOH (2S,3S)- (2R,3S)- (5) (6) (7) (8) meso form (内消旋体内消旋体) The meso form is achiral Mole. * * Diastereomer: (7) (5) (6) The relationship between diastereomers is not related as an object and its mirror image. 7.6 Resolution of Enantiomers （对映体的拆分）（对映体的拆分） Pasteur: C C COO Na+ COO

27、NH4+ H H OH HO Sodium ammonium tartrate (酒石酸铵钠酒石酸铵钠) Recrystallization (重结晶重结晶) Two kind crystals are mirror image 7.5.3 Physical Properties of Stereoisomer Louis Pasteur 1822-1895 The scientific contributions of Pasteur were among the most valuable in the history of science, and he is claimed equal

28、ly 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. C COO H HO CH3 C CH3 H HO