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Chapter 12 Carbohydrates. Chapter 132 Carbohydrates Synthesized by plants using sunlight to convert CO 2 and H 2 O to glucose and O 2. Polymers include.

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Presentation on theme: "Chapter 12 Carbohydrates. Chapter 132 Carbohydrates Synthesized by plants using sunlight to convert CO 2 and H 2 O to glucose and O 2. Polymers include."— Presentation transcript:

1 Chapter 12 Carbohydrates

2 Chapter 132 Carbohydrates Synthesized by plants using sunlight to convert CO 2 and H 2 O to glucose and O 2. Polymers include starch and cellulose. Starch is storage unit for solar energy. Most sugars have formula C n (H 2 O) n, “hydrate of carbon.”

3 Chapter 123 Classification of Carbohydrates Monosaccharides or simple sugars – polyhydroxyaldehydes or aldoses – polyhydroxyketones or ketoses Disaccharides can be hydrolyzed to two monosaccharides. Polysaccharides hydrolyze to many monosaccharide units. E.g., starch and cellulose have > 1000 glucose units.

4 Chapter 124 Monosaccharides Classified by: – aldose or ketose – number of carbons in chain – configuration of chiral carbon farthest from the carbonyl group glucose, a D -aldohexose fructose, a D -ketohexose =>

5 Chapter 125 D and L Sugars D sugars can be degraded to the dextrorotatory (+) form of glyceraldehyde. L sugars can be degraded to the levorotatory (-) form of glyceraldehyde.

6 Chapter 236 The D Aldose Family

7 Chapter 127 Epimers Sugars that differ only in their stereochemistry at a single carbon.

8 Chapter 128 Cyclic Structure for Glucose Glucose cyclic hemiacetal formed by reaction of -CHO with -OH on C5. D-glucopyranose

9 Chapter 129 Cyclic Structure for Fructose Cyclic hemiacetal formed by reaction of C=O at C2 with -OH at C5. D-fructofuranose

10 Chapter 1210 Anomers

11 Chapter 1211 Mutarotation Glucose also called dextrose; dextrorotatory.

12 Chapter 1212 Epimerization In base, H on C2 may be removed to form enolate ion. Reprotonation may change the stereochemistry of C2.

13 Chapter 1213 Reduction of Simple Sugars C=O of aldoses or ketoses can be reduced to C-OH by NaBH 4 or H 2 /Ni. Name the sugar alcohol by adding -itol to the root name of the sugar. Reduction of D -glucose produces D -glucitol, commonly called D -sorbitol. Reduction of D -fructose produces a mixture of D -glucitol and D -mannitol.

14 Chapter 1214 Oxidation by Nitric Acid Nitric acid oxidizes the aldehyde and the terminal alcohol; forms aldaric acid.

15 Chapter 1215 Oxidation by Tollens Reagent Tollens reagent reacts with aldehyde, but the base promotes enediol rearrangements, so ketoses react too. Sugars that give a silver mirror with Tollens are called reducing sugars.

16 Chapter 2316 Nonreducing Sugars Glycosides are acetals, stable in base, so they do not react with Tollens reagent. Disaccharides and polysaccharides are also acetals, nonreducing sugars.

17 Chapter 2317 Formation of Glycosides React the sugar with alcohol in acid. Since the open chain sugar is in equilibrium with its  - and  -hemiacetal, both anomers of the acetal are formed. Aglycone is the term used for the group bonded to the anomeric carbon.

18 Chapter 2318 Ether Formation Sugars are difficult to recrystallize from water because of their high solubility. Convert all -OH groups to -OR, using a modified Williamson synthesis, after converting sugar to acetal, stable in base.

19 Chapter 1219 Ester Formation Acetic anhydride with pyridine catalyst converts all the oxygens to acetate esters.

20 Chapter 2320 Osazone Formation Both C1 and C2 react with phenylhydrazine.

21 Chapter 1221 Kiliani-Fischer Synthesis This process lengthens the aldose chain. A mixture of C2 epimers is formed.

22 Chapter 1222 Fischer’s Proof Emil Fischer determined the configuration around each chiral carbon in D -glucose in 1891, using Ruff degradation and oxidation reactions. He assumed that the -OH is on the right in the Fischer projection for D -glyceraldehyde. This guess turned out to be correct!

23 Chapter 1223 Disaccharides Three naturally occurring glycosidic linkages: 1-4’ link: The anomeric carbon is bonded to oxygen on C4 of second sugar. 1-6’ link: The anomeric carbon is bonded to oxygen on C6 of second sugar. 1-1’ link: The anomeric carbons of the two sugars are bonded through an oxygen.

24 Chapter 1224 Cellobiose Two glucose units linked 1-4’. Disaccharide of cellulose. A mutarotating, reducing sugar.

25 Chapter 1225 Maltose Two glucose units linked 1-4’.

26 Chapter 1226 Lactose Galactose + glucose linked 1-4’. “Milk sugar.”

27 Chapter 1227 Sucrose Glucose + fructose, linked 1-1’ Nonreducing sugar

28 Chapter 1228 Cellulose Polymer of D -glucose, found in plants. Mammals lack the  -glycosidase enzyme.

29 Chapter 1229 Amylose Soluble starch, polymer of D -glucose. Starch-iodide complex, deep blue.

30 Chapter 1230 Amylopectin Branched, insoluble fraction of starch.

31 Chapter 1231 Glycogen Glucose polymer, similar to amylopectin, but even more highly branched. Energy storage in muscle tissue and liver. The many branched ends provide a quick means of putting glucose into the blood.

32 32 End of Chapter 12


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