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1、Chapter 7Stereochemistry,7.1Molecular Chirality: Enantiomers,A molecule is chiral if its two mirror image forms are not superposable upon one another. A molecule is achiral if its two mirror image forms are superposable.,Chirality,Br,Cl,H,F,Bromochlorofluoromethane is chiral,It cannot be superposed
2、point for point on its mirror image.,Br,Cl,H,F,Bromochlorofluoromethane is chiral,H,Cl,Br,F,To show nonsuperposability, rotate this model 180 around a vertical axis.,Br,Cl,H,F,Bromochlorofluoromethane is chiral,H,Cl,Br,F,Another look,are enantiomers with respect to each other,and,nonsuperposable mir
3、ror images are called enantiomers,Enantiomers,Isomers,stereoisomers,constitutional isomers,Isomers,stereoisomers,constitutional isomers,diastereomers,enantiomers,Chlorodifluoromethaneis achiral,Chlorodifluoromethaneis achiral,The two structures are mirror images, but are not enantiomers, because the
4、y can be superposed on each other.,7.2The Stereogenic Center,a carbon atom with fourdifferent groups attached to it also called: chiral centerasymmetric centerstereocenter,The Stereogenic Center,A molecule with a single stereogenic center is chiral. Bromochlorofluoromethane is an example.,Chirality
5、and stereogenic centers,Cl,F,Br,H,A molecule with a single stereogenic center is chiral. 2-Butanol is another example.,Chirality and stereogenic centers,CH3,OH,H,CH2CH3,Examples of molecules with 1 stereogenic center,a chiral alkane,Examples of molecules with 1 stereogenic center,Linalool, a natural
6、ly occurring chiral alcohol,Examples of molecules with 1 stereogenic center,1,2-Epoxypropane: a stereogenic center can be part of a ring,attached to the stereogenic center are: H CH3 OCH2 CH2O,Examples of molecules with 1 stereogenic center,Limonene: a stereogenic center can be part of a ring,attach
7、ed to thestereogenic center are: H CH2CH2 CH2CH= C=,Examples of molecules with 1 stereogenic center,Chiral as a result of isotopic substitution,A molecule with a single stereogenic centermust be chiral.,But, a molecule with two or more stereogenic centers may be chiral or it may not (Sections 7.10-7
8、.13).,7.3Symmetry in Achiral Structures,Symmetry tests for achiral structures,Any molecule with a plane of symmetryor a center of symmetry must be achiral.,A plane of symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry.,Plane of symmetry,A plane of
9、 symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry.,Plane of symmetry,A plane of symmetry bisects a molecule into two mirror image halves.1-Bromo-1-chloro-2-fluoroethene has a planeof symmetry.,Plane of symmetry,A plane of symmetry bisects a mole
10、cule into two mirror image halves.1-Bromo-1-chloro-2-fluoroethene has a planeof symmetry.,Plane of symmetry,A point in the center of themolecule is a center of symmetry if a line drawn from it to some element, when extended an equal distance in the opposite direction, encounters an identical element.,Center of symmetry,A point in the center of themolecule is a center of symmetry if a line drawn from it to any element, when extended an equal distance in the opposite direction, encounters an identical element.,Center of symmetry,
