有机化学Chapter 7. Stereochemistry立体化学.

1、Chapter 7 Stereochemistry7.1 Molecular Chirality and Enantiomers Characteristic of enantiomers Chiral molecules Chirality7.2 Molecular Symmetry and Asymmetric Molecules Symmetric elements Achiral Molecules7.3 Properties of Chiral Molecules: Optical Activity7.4 Representation and Nomenclature of Chir

2、al MoleculesA. Representation Fischer projectionsB. Naming enantiomers with one stereocenter by R-S notational system 7.5 Chiral Molecules With Two Stereocenters7.5.1 Chiral Molecules With Two Different Stereocenter： Diastereomers7.5.2 Stereoisomers With Two Same Stereocenters Meso-form7.5.3 Physica

3、l Properties of Stereoisomer7.6 Resolution of EnantiomersCis-,TransMolecular structureMolecular 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. constitutionThe different spatial arrangement of atoms

4、or groupsEnantiomers(对映异构体对映异构体)Diastereomers(非对映异构体非对映异构体)The formeris unchang-ed by rota-tion of C-CSingle bondConfigurational isomers?Molecular confor-mation(构象构象)Conformers: The same configurationThe different spatial arrangement of atoms or groups by rotation of C-C singlebondThe atoms are bond

5、ed 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. Bromochlorofluoromethane:turn 180CHClBr

6、FCBrHClFCClFBrHCCH3HOHCH2CH3COHCH3HH3CH2CEnantiomersCharacteristic of enantiomers The same molecular constitution.2. The relationship of enantiomers:object and mirror image 3. Nonsuperposable 4. The same physical properties, the similar chemical properties. Chiral molecules: with its enantiomerChira

7、lity: Mole. isnt superposable withtheir mirror imageStereocenter or stereogenic center,asymmetric center.H2CCOHCH3*1,2-Epoxypropane(1,2-环氧丙烷环氧丙烷)CCH2CH3HCH3123456Limonene(柠檬油精柠檬油精)* The molecule that contains one chiral center have a pair of enantiomersCDHClCH3CDCH3ClHAn isotopeChiral center: the ca

8、rbon with 4 different groups. Ex.2-butanol: C2CCOOHCH3HHO(-)-Lactic acid(乳酸乳酸)CHDCH3ClCDHCH3ClAchiral center: a C atom is attached by 2 or more same groups. CHClFHturn 180turn 180Achiral molecule(非手性分子非手性分子).CClHHFThe molecule is achiral and is superposable with its mirror image.7.2 Molecular Symmet

9、ry and Asymmetric MoleculesSymmetric 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 other half.P180,6.2Ex. 2-Chloropropane2. All atoms in a molecule are on a plane.Ex. (E)-1,2-DichloroetheneB. Center of symmetry(i)（对称点）（对称

10、点） If any straight line passes a atom and molecularcenter, the same atom or group is encounteredon the site at equal distance but in the oppositedirection. Ex.trans-2,4-dichloro-1,3-difluorocyclo- butaneFFClClHH HHAny molecule with a plane of symmetryor a center of symmetry-Achiral moleculeA symmetr

11、ic molecule.Any chiral molecule is asymmetric one.Nonsuperposable with its mirror image andhave a enantiomer.7.3 Properties of Chiral Molecules: 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 planarpolarization

12、 rotates. Polarimeter(旋光仪旋光仪):To measure the effect of plane-polarized light on optically active compoundsLight source Polarizer Sample 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)

13、Nat: temp.P184t=c*lSeparate enantiomers rotate the plane of plane-polarized light equal amounts and inopposite direction.Optically compoundsOne enantiomer Levo-(左旋左旋-) anticlockwise(-)Other enantiomer Dextro- (右旋右旋) clockwise(+)(-)-2-Butanol, (+)-2-ButanolThe mixtures that contain equal amounts of e

14、nantiomers are Racemic(外消旋外消旋). ()-2-ButanolJean Baptiste BiotFrench Physicistb. 1774d. 1862Jean Baptiste Biotwas born in Paris,France, and was educated there at the cole poly-technique.His work on determiningthe optical rotation of naturally occureing molecules included anexperiment on turpentine.7

15、.4 Representation and Nomenclature of Chiral MoleculesA. Representation:1. Wedge and dash drawing(伞式伞式):CHHOCOOHCH3COHHHOOCCH3(+)-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

16、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. CHHOCH3CH2CH3(-)-2-ButanolCH3CH2CH3HOHCCH3CH2CH3HHO Vertical line represents the bond that project behind

17、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 line 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-ButanolHermann Emil FischerGermany BerlinUniversity Berlin, Germany b. 1852d. 1919Generally considered the great

18、est organic chemist of his time, Fischer received the 1902 NobelPrize in Chemistry for his work on carbohydrates and purines. His discovery that phenylhydrazine reacts with carbohydrates to form osazones enabled him to elucidatethe stereochemistry of sugars. First to synthesize adenine and guanine,

19、he made the first synthetic nucleotides. Among many other contributions was his work onprotein structure and synthesis, the lock-and-key model for enzymereactions, structure of triarylmethane dyes, and the design of laboratory hoods and safety equipment.CH3CH2CH3BrHCH3BrHCH3CH2Characteristics of Fis

20、cher projection One group is fixed, the other three groups are rotated in turn, the configuration is not changed. To exchange any two groups, the configuration was changed, the other enantiomer was got. CH3CH2CH3BrHCH2CH3CH3HBr(-)-2-Bromobutane(+)-BrCH3CH2CH3H(+)-turn 109.5(-)-(+)-(+)-B. Naming enan

21、tiomers with one stereocenter by R-S notational systemDesignation 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.CCH3CH2CH3HHO(-)-2-ButanolOH CH2CH3CH3 HCH3EtHOH3. Draw t

22、he tree highest ranked substituent from the highest one to lowest one. The direction:Clockwise: ( R )-Anticlockwise: ( S )-OHCH3CH2CH3CH3HOCH2CH3H(R)-2-ButanolP194HOHCH3Et(-)-Lactic acidCHOHCOOHCH3CHH3COHCOOH7.5 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

23、 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 acidCOOHCH3HHOHOHCOOHCH3HOHOHHCOOHCH3HHOHHOCOOHCH3HOHHOH(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)Normally n stereocenters 2n stereoisomers

24、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)COOHHOHHOHCOOHCOOHCOOHHHOHOH7.5.2 Stereoisomers With Two Same StereocentersEx. Tartaric acid(酒石酸酒石酸)COOHHHOHHOCOOH(2R,3R)-*COOHHOHOHHCOOH(2S,3S)-(2R,3S)-(5) (6) (7) (8)meso form(内消旋体内消旋体)The meso form is a

25、chiral Mole.*Diastereomer:(7)(5)(6)The relationship between diastereomersis not related as an object and its mirrorimage.7.6 Resolution of Enantiomers （对映体的拆分）（对映体的拆分）Pasteur: CCCOO Na+COO NH4+HHOHHOSodium ammonium tartrate(酒石酸铵钠酒石酸铵钠)Recrystallization(重结晶重结晶)Two kind crystalsare mirror image7.5.3 P

26、hysical Properties of StereoisomerLouis Pasteur1822-1895 The scientific contributions of Pasteur were among the most valuable in the history of science,and he is claimed equally by chemistry and microbiology. Best known to chemists for his work on the tartaric acids, he recognized the structural rel

27、ationships (now called chirality)responsible for optical isomerism, and that microorganisms can distinguish between enantiomers. Pasteur also showed that micro-organisms cause fermentation andvarious diseases, and he developed methods for pasteurization and for vaccination against anthrax and rabies. His work saved t