Chapter 11 Carbohydrates 6 2 Draw the Fischer projection structures of all of the trioses. Ans: 0 0 CH2OH C-H C -H C=0 H-C-OH HO-C-H CH2OH CH2OH CH2OH dihydroxyacetone D-glyceraldehyde L-glyceraldehyd Structures shown in Figure 11.1. Section:11.1 and Figure 11.1 3 What is the difference between an enantiomer and a diastereoisomer? Ans:An enantiomer is a stereoisomer that is a perfect(nonsuperimposable or nonidentical) mirror image.A chiral molecule has one perfect mirror image.But for larger carbohydrates that have the same chemical formula and have multiple chiral centers,variations in asymmetric carbon structures mean that additional stereoisomers exist.The stereoisomers that are not mirror images of each other are called diastereoisomers. Section:11.1 4 How is the D or L configuration determined? Ans:The D or L designation is determined by the asymmetric carbon farthest from the ketone or aldehyde group,and is related to the glyceraldehyde D and L structures. Section:11.1 5 Draw the Haworth projections of the two pyranose forms of D-glucose. Ans: CH2OH CH2OH OH OH OH OH OH OH OH a-D-glycopyranose B-D-glucopyranose as shown in Figure 11.4 of the text. Section:11.1 6 Draw the structure of lactose.Identify the monosaccharides involved and identify the type of linkage in lactose? Ans: D-glucose (a anomer) CH2OH D-galactose 0 CH2OH OH OH OH OH OH OH B 1-4 glycosidic linkage Section:11.2Chapter 11 Carbohydrates 6 2 Draw the Fischer projection structures of all of the trioses. Ans: CH2OH C CH2OH O C C CH2OH O H H OH C C CH2OH O H HO H dihydroxyacetone D-glyceraldehyde L-glyceraldehyde Structures shown in Figure 11.1. Section: 11.1 and Figure 11.1 3 What is the difference between an enantiomer and a diastereoisomer? Ans: An enantiomer is a stereoisomer that is a perfect (nonsuperimposable or nonidentical) mirror image. A chiral molecule has one perfect mirror image. But for larger carbohydrates that have the same chemical formula and have multiple chiral centers, variations in asymmetric carbon structures mean that additional stereoisomers exist. The stereoisomers that are not mirror images of each other are called diastereoisomers. Section: 11.1 4 How is the D or L configuration determined? Ans: The D or L designation is determined by the asymmetric carbon farthest from the ketone or aldehyde group, and is related to the glyceraldehyde D and L structures. Section: 11.1 5 Draw the Haworth projections of the two pyranose forms of D-glucose. Ans: O OH OH CH2OH OH OH O OH OH CH2OH OH OH α-D-glycopyranose β-D-glucopyranose as shown in Figure 11.4 of the text. Section: 11.1 6 Draw the structure of lactose. Identify the monosaccharides involved and identify the type of linkage in lactose? Ans: O OH OH CH2OH OH O OH OH CH2OH O OH  1-4 glycosidic linkage D-glucose ( anomer) D-galactose Section: 11.2