Ch25 - C hapter 24 Carbon-Carbon Bond Formation and...

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Chapter 25: Carbohydrates Solutions 715 CHAPTER 25 Solutions to the Problems Problem 25.1 Draw Fischer projections for all 2-ketopentoses. Which are D-2-ketopentoses, which are L-2-ketopentoses, and which are enantiomers? CH 2 0H CH 2 2 2 I I I I C=O H+OH H:t=H Hi=H :t=oH H . OH HO H H H H 2 2 2 2 \. D-Ribulose L-Ribulose) \. . D-Xylulose L-Xylulose) y V, a pair of enantiomers - a pair of enantiomers Problem 25.2 Mannose exists in aqu~ous solution as a mixture of a-D-mannopyranose and ~-D-mannopyranose. Draw Haworth projections for these molecules. D-Mannose differ~ in configuration from D-glucose at carbon-2. Therefore, the alpha and beta forms of D-. mannopyranose dIffer from those of alpha and beta D-glucopyranoses only in the orientation of the -OH on carbon-2. . Following are Haworth projections for these compounds. Ha:H2~oH OH(~) H Ha:H200H Configuration differs .' OH HO 1 . 1 from that of D-glucos.e OH(a) H0!'l. . at 5"2 '. H H H H~ . a-D-Mannopyranose ~- D-Mannopyranose (a-D-Mannose) (~-D~Mannose) Problem 25.3 Draw chair conformations for a-D-mannopyranose and ~-D-mannopyranose. Label the anomeric carbon in each. D-Mannose differs in configuration from D-glucose at carbon-2. Draw chair conformations for the alpha and beta forms of D-glucopyranose and then invert the configuration of the -OH on carbon-2. For reference the open chain form of D-mannose is also drawn. ' . HOCH 2 2 2 H~?~b ." H~?~OH 0 ~H~~~ n~OH(~ n~~ ~ Anoleric "H Anomeric /OH(ex) carbon atom .carbon atom ~-D-Mannopyranose D-Mannose a-D~Mannopyranose (~-D-Mannose) (a-D-Mannose)
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Chapter 25: Carbohydrates Solutions 716 :emblem 25.4 Draw a Haworth projection and a chafr conformation for methyl a-o-mannopyranoside (methyl 0.-0-. mannoside). Label the anomeric carbon and the glycosidic bond. a-t 2 OH , HOCH 2 H~_OH H.,-{) Anomenc . ~ carbon atom 1 ... An 'a-glycosidic OCH:3(a) bond Methyl a-D-mannopyranoside (Chair confor.mation) Problem 25.5 Draw a stnIClUra~ formula for the ~-N-glycoside formed between 2-deoxy-o-ribofuranose and adenine. Following are structural formulas for adenine, the· monosaccharide hemiacetal, and the N-glycoside. Adffim' &N) :XN~ N - ~N . ~t I ) H ~N N --:. .. A fl-N-glycosidic + ~O bond HOCV~H ... . Anomeric carbon ~r---r~ HO f\-2-Deoxy-D-RibOfuranose Problem 25.6 Draw a chair conformation for ihe a form of a disaccharide in which two units of o-glucopyranose are joined by a 13-1 ,3-glycosidic bond. H~~~· OH1\~ ~-1,3-glycosidic OH bond ' Monosaccharides Problem 75.7 Explain the meaning of the designations 0 and Las Llsed to specify the configuration of monosaccharides. The designations Dand L refer to the configuration of the chiral center farthest from the carbonyl group of the monosaccharide. When a monosaccharide is drawn in a Fischer projection, the reference -OH is on the right in a D-monosaccharide and on the left in an L-monosaccharide. Note that the conventions Dand L specify the configuration at one and only one of however man)' chiral centers there are in a particular monosaccharide.
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This note was uploaded on 07/09/2011 for the course CHE 301 taught by Professor Diver during the Spring '08 term at SUNY Buffalo.

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Ch25 - C hapter 24 Carbon-Carbon Bond Formation and...

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