A symmetric objectthathasasuperimposablemirrorimage

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Unformatted text preview: y) possible in organic mo lecules. · An asymmetric object that is not superimposable on its mirror image and is called chiral. The right and left hands are mirror images of one another that are not super­ imposable and are therefore chiral. · A symmetric object that has a superimposable mirror image is called achiral. Many commo n objects such as shoes and scissors are chiral, while a glass and soccer ball are examples of achiral objects. Chiral objects Achiral objects · A carbon atom that possesses four different functional groups is called a chiral carbon and forms non­superimposable mirror images. Chiral Achiral 3 Chemistry 52 Chapter 26 CHIRAL MOLECULES Examples: 1. Ident ify each of the fo llowing structures as chiral or achiral. If chiral, indicate the chiral carbon. a) b) 2. Ident ify all the chiral carbons in each of the fo llowing mo lecules: a) b) H C 3 H O H C 3 Cl CH3 OH HO c) NH 2 d) HO 3. Label the 4 chiral carbons in amo xicillin, an antibiotic in the family o f penicillins. 4 Chemistry 52 Chapter 26 FISHER PROJECTIONS · Chemists use Fisher projections to show the bonds to a chiral atom. · In these diagrams, the bonds to the chiral atom are drawn as intersect ing lines, with the chiral carbon being at the center of the intersecting lines. · The horizontal lines represent the bonds that come forward in the three­dimensio nal structure (bold wedges), and the vert ical lines represent the bonds that that point away (dash lines). Fisher projections · Fisher project ions can also be wr itten for larger compounds that have two or more chiral carbons. For example, the two mirror images shown below are different. Each chiral carbon is bonded to four different groups. CH3 CH3 H Br Br H Br H H CH3 Br CH3 · Note that when drawing Fisher projections for mirror images, the position o f the subst ituents on the horizontal line are reversed while the groups on the vertical lines are left unchanged. 5 Chemistry 52 Chapter 26 FISHER PROJECTIONS · Similarly th...
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