PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 681Stereochemistry•Recall that isomers are different compounds with the same molecular formula.•The two major classes of isomers are constitutional isomers and stereoisomers.Constitutional/structural isomers have different IUPAC names, the same or different functional groups, different physical properties and different chemical properties.Stereoisomers differ only in the way the atoms are oriented in space. They have identical IUPAC names (except for a prefix like cis or trans). They always have the same functional group(s).•A particular three-dimensional arrangement is called a configuration. Stereoisomers differ in configuration.The Two Major Classes of Isomers2Figure 5.3A comparison of consitutionalisomers and stereoisomers3Are the following pairs of compounds consitutional isomers or stereoisomers?a)b)c)constitutionalconstitutionalstereoisomer4•Although everything has a mirror image, mirror images may or may not be superimposable. •Some molecules are like hands. Left and right hands are mirror images, but they are not identical, or superimposable. Chiral and Achiral Molecules5•Other molecules are like socks. Two socks from a pair are mirror images that are superimposable. A sock and its mirror image are identical.•A molecule or object that is superimposable on its mirror image is said to be achiral. •A molecule or object that is not superimposable on its mirror image is said to be chiral.6•We can now consider several molecules to determine whether or not they are chiral.7•The molecule labeled A and its mirror image labeled B are not superimposable. No matter how you rotate A and B, all the atoms never align. Thus, CHBrClF is a chiral molecule, and A and B are different compounds.•A and B are stereoisomers—specifically, they are enantiomers.•A carbon atom with four different groups is a tetrahedral stereogenic center.8•In general, a molecule with no stereogenic centers will not be chiral. There are exceptions to this that will be considered in Chapter 17.•With one stereogenic center, a molecule will always be chiral.•With two or more stereogenic centers, a molecule may or may not be chiral.•Achiral molecules usually contain a plane of symmetry but chiral molecules do not. •A plane of symmetry is a mirror plane that cuts the molecule in half, so that one half of the molecule is a reflection of the other half.910Summary of the Basic Principles of Chirality:•Everything has a mirror image. The fundamental question is whether the molecule and its mirror image are superimposable.•If a molecule and its mirror image are not superimposable, the molecule and its mirror image are chiral.•The terms stereogenic center and chiral molecule are related but distinct. In general, a chiral molecule must have one or more stereogenic centers.•The presence of a plane of symmetry makes a molecule achiral.11Clasiffy each of the following pairs as chiral or achiral.a)CH3ClCH3BrCH3ClH3CBrb)CH3ClBrHCH3ClBrHFHBrFHBrc)achiralchiralchiral12•To locate a stereogenic center, examine each tetrahedral carbon atom in a molecule, and look at the four groups—not the four atoms—bonded to it.•Always omit from consideration all C atoms that cannot be tetrahedral stereogenic centers. These includeCH2 and CH3 groupsAny sp or sp2 hybridized C Stereogenic Centers13•Larger organic molecules can have two, three or even hundreds of stereogenic centers.14Label the stereogenic centers in each molecule and decide if it is chiral.a) CH3CH2CH(Cl)CH2CH3HClachiralb) CH3CH(OH)CH=CH2HOHchiralc) (CH3)2CHCH2CH2CH(CH3)CH2CH3HCH3chiral15How many stereogenic centers does each molecule have?a)BrBrb)16c)H2NHNNHOHCO2HOSHOOOnly carbons attached to four different groups.17•To draw both enantiomers of a chiral compound such as 2-butanol, use the typical convention for depicting a tetrahedron: place two bonds in the plane, one in front of the plane on a wedge, and one behind the plane on a dash. Then, to form the first enantiomer, arbitrarily place the four groups—H, OH, CH3 and CH2CH3—on any bond to the stereogenic center. Then draw the mirror image.18Figure 5.5Three-dimensionalrepresentations for pairsof enantiomers19Locate each stereogenic center and draw both enantiomers. a) CH3CH(Cl)CH2CH3HClHClb)CH3CH2CH2CH(NH2)COOHCO2HH NH2HO2CHH2N20•Stereogenic centers may also occur at carbon atoms that are part of a ring.•To find stereogenic centers on ring carbons, always draw the rings as flat polygons, and look for tetrahedral carbons that are bonded to four different groups.21•In 3-methylcyclohexene, the CH3 and H substituents that are above and below the plane of the ring are drawn with wedges and dashes as usual.22Locate the stereogenic center in the following:a)No stereogenic centers.b)O23•Since enantiomers are two different compounds, they need to be distinguished by name. This is done by adding the prefix R or S to the IUPAC name of the enantiomer.•Naming enantiomers with the prefixes R or S is called the Cahn-Ingold-Prelog system.•To designate enantiomers as R or S, priorities must be assigned to each group bonded to the stereogenic center, in order of decreasing atomic number. The atom of highest atomic number gets the highest priority (1).Labeling Stereogenic Centers with R or S24•If two atoms on a stereogenic center are the same, assign priority based on the atomic number of the atoms bonded to these atoms. One atom of higher atomic number determines the higher priority.25•If two isotopes are bonded to the stereogenic center, assign priorities in order of
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