Chapter 24 Carbohydrates

Transcription

1 hapter arbohydrates Review of oncepts Fill in the blanks below. To verify that your answers are correct, look in your textbook at the end of hapter. Each of the sentences below appears verbatim in the section entitled Review of oncepts and Vocabulary. arbohydrates are polyhydroxy or ketones. Simple sugars are called and are generally classified as aldoses and. For all D sugars, the chirality center farthest from the carbonyl group has the configuration. Aldohexoses can form cyclic hemi that exhibit a pyranose ring. yclization produces two stereoisomeric hemiacetals, called. The newly created chirality center is called the carbon. In the α anomer, the hydroxyl group at the anomeric position is to the group, while in the β anomer, the hydroxyl group is to the group. Anomers equilibrate by a process called, which is catalyzed by either or. Some carbohydrates, such as D-fructose, can also form five-membered rings, called rings. Monosaccharides are converted into their ester derivatives when treated with excess. Monosaccharides are converted into their ether derivatives when treated with excess and silver oxide. When treated with an alcohol under acid-catalyzed conditions, monosaccharides are converted into acetals, called. Both anomers are formed. Upon treatment with sodium borohydride an aldose or ketose can be reduced to yield an. When treated with a suitable oxidizing agent, an aldose can be oxidized to yield an. When treated with N, an aldose is oxidized to give a dicarboxylic acid called an. D-Glucose and D-mannose are epimers and are interconverted under strongly conditions. The Kiliani-Fischer synthesis can be used to lengthen the chain of an. The Wohl degradation can be used to shorten the chain of an. are comprised of two monosaccharide units, joined together via a glycosidic linkage. Polysaccharides are polymers consisting of repeating monosaccharide units linked by bonds. When treated with an in the presence of an acid catalyst, monosaccharides are converted into their corresponding N-glycosides.

2 0 APTER Review of Skills Fill in the blanks and empty boxes below. To verify that your answers are correct, look in your textbook at the end of hapter. The answers appear in the section entitled SkillBuilder Review.. Drawing the yclic emiacetal of a ydroxyaldehyde DRAW TE YLI EMIAETAL TAT IS FRMED WEN TE FLLWING YDRXYALDEYDE UNDERGES YLIZATIN UNDER AIDI NDITINS. [ ].: Drawing a aworth Projection of an Aldohexose DRAW A AWRT PRJETIN F α-d-galatpyranse. [ ] D-GALATSE.: Drawing the More Stable hair onformation of a Pyranose Ring DRAW TE MRE STABLE AIR NFRMATIN F α-d-galatpyranse. α-d-galatpyranse MRE STABLE AIR NFRMATIN. Identifying a Reducing Sugar STEP - IDENTIFY TE PSITIN. STEP - DETERMINE IF TE GRUP ATTAED T TE ANMERI PSITIN IS A GRUP R GRUP. - IF GRUP, TEN TE MPUND IS A REDUING SUGAR - IF GRUP, TEN TE MPUND IS NT A REDUING SUGAR.

3 APTER. Determining Whether a Disaccharide Is a Reducing Sugar STEP - IDENTIFY TE PSITINS. STEP - DETERMINE IF TE GRUPS ATTAED T TE ANMERI PSITINS ARE YDRXY GRUPS R ALKXY GRUPS. - IF NE IS A GRUP, TEN TE MPUND IS A REDUING SUGAR. - IF NEITER ARE GRUPS, TEN TE MPUND IS NT A REDUING SUGAR. Review of Reactions Identify the reagents necessary to achieve each of the following transformations. To verify that your answers are correct, look in your textbook at the end of hapter. The answers appear in the section entitled Review of Reactions. emiacetal Formation hain Lengthening and hain Shortening

4 APTER Reactions of Monosaccharides Ac Ac Ac Ac Ac Solutions.. an aldohexose an aldopentose c) a ketopentose d) an aldotetrose e) a ketohexose.. Both are hexoses so both have molecular formula ( ). Although they have the same molecular formula, they have different constitution one is an aldehyde and the other is a ketone. Therefore, they are constitutional isomers... All are D sugars except for (, which is an L sugar. S, S, R, R R, S, S c) R, R d) S, R e) S, S, R Pay special attention to the following trend: The configuration of each chirality center is R when the group is on the right side of the Fischer projection, and the configuration is S when the group is on the left side...

5 APTER.. D L enantiomers.. D L D L enantiomers enantiomers.7. L-Fructose.8. D-fructose and D-glucose are constitutional isomers. Both have molecular formula ( ). Although they have the same molecular formula, they have different constitution one is a ketone, and the other is an aldehyde. D-Fructose D-Glucose

6 APTER.9. c) d).0... The six-membered ring is expected to predominate because it has less ring strain than a five-membered ring... c) d) e) f).. β-d-galactopyranose

7 APTER.. A B α-d-mannopyranose β-d-mannopyranose.. A B α-d-talopyr anose β-d-talopyr anose.. c).7. D-Allose

8 APTER.8. more stable ring flip less stable.9. c) d).0. L-TRESE

9 APTER 7.. D-Fructose.. D-Fructose.. excess Ac py Ac Ac Ac Ac Ac excess Ac Ac Ac py Ac Ac Ac excess Ac Ac Ac c) py Ac Ac Ac

10 8 APTER.. excess I Ag excess I Ag c) excess I Ag.. l Et Et Et Et Et Et Et Et

11 APTER 9.. A A.7. D-Mannose D-Allose c) D-Galactose.8. NaB Rotate 80 D-Altose NaB D-Talose

12 0 APTER.9. NaB Rotate 80 D-Allose NaB L-Allose.0. The following alditols are meso compounds, and are therefore optically inactive: NaB D-Allose (meso) D-Galactose.. NaB (meso) No (an acetal) Yes c) Yes

13 APTER.. D-Galactonic acid D-Galactonic acid c) D-Gluconic acid d) D-Gluconic acid.. This compound will not be a reducing sugar because the anomeric position is an acetal group. β-d-glucopyranose pentamethyl ether.. D-Ribose Fischer-Kiliani D-Allose D-Altose D-Xylose Fischer-Kiliani D-Gulose D-Idose c) D-Lyxose Fischer-Kiliani D-Galactose D-T alose

14 APTER.. D-Erythrose ) N ), Pd / BaS, D-Ribose D-Arabinose.. Wohl Degradation D-Allose D-Altose D-Ribose.7. ) N ) Ac ) NaMe D-Ribose D-Erythrose.8. Wohl Degradation Fischer- Kiliani D-Glucose D-Arabinose D-Glucose D-Mannose.9. Yes, one of the anomeric positions bears an group. No, both anomeric positions bear acetal groups. c) No, both anomeric positions bear acetal groups.

15 APTER.0. NaB Me.. NaB Br c) l d) Ac py Ac Ac Ac Ac Ac Ac Ac Ac.. a D-aldotetrose an L-aldopentose c) a D-aldopentose d) a D-aldohexose e) a D-ketopentose.. D-glyceraldehyde L-glyceraldehyde c) D-glyceraldehyde d) L-glyceraldehyde.. D-Glucose D-Mannose c) D- Galactose d) L-Glucose

16 APTER.. D-Ribose D-Arabinose c) L-Ribose d) Same compound e) Diastereomers.. c) D-ribose α pyranose ring β pyranose ring D-ribose α furanose ring β furanose ring.9. epimers diastereomers c) enantiomers d) identical compounds

17 APTER.0. D-Glucose.. R R R R S c) R S R d) R S R R e) S R.. D-Glucose D-Galactose c) D-Mannose d) D-Allose.. c) d).... α-d-allopyranose β-d-galactopyranose c) methyl β-d-glucopyranoside

18 APTER.. D-Allose D-Galactose c) D-Glucose.7. Ac Ac Ac Ac Ac c).8. The product is a meso compound meso compound.9. D-Allose N, heat optically inactive meso compound

19 APTER 7.0. equatorial equatorial axial axial axial.. excess I Ag.. diastereomers same compound.... D-Allose Wohl degradation Wohl degradation D-Altose D-Ribose

20 8 APTER.. Kiliani-Fischer D-Arabinose D-Glucose D-Mannose.. N N N D-Glycer ald ehyde Diastereomers.7. NaB L-Gulose.8. D-Allose and D-Galactose.9. This compound will not be a reducing sugar because the anomeric position is an acetal group. This compound will be a reducing sugar because the anomeric position bears an group.

21 APTER 9.70., l, l c) N,, heat d) excess I, Ag followed by α-d-glucopyranose and β-d-glucopyranose α-d-galactopyranose and β-d-galactopyranose D-Arabinose D-Ribose and D-xylose c) D-xylose d) D-xylose NaB D-Xylose D-Xylitol.7. Isomaltose (a -α-glycoside)

22 0 APTER.7. No, it is not a reducing sugar because the anomeric position has an acetal group. c) Salicin is a β-glycoside. salicin Ac d) salicin e) No. In the absence of acid catalysis, the acetal group is not readily hydrolyzed. py Ac Ac Ac Ac Ac.77. l - l.78. N an α-n-glycoside N a β-n-glycoside

23 APTER.79. N N N N N N N N N N DEXY- ADENSINE GUANSINE.80. NaB NaB NaB NaB (optically active) (optically active) (optically inactive) (optically inactive).8. c) Yes. The compound has chirality centers, and it is not a meso compound. Therefore, it will be optically active. d) The gluconic acid is a carboxylic acid and its IR spectrum is expected to have a broad signal between 00 and 00 cm -. The IR spectrum of the lactone will not have this broad signal.

24 APTER.8. In order for the group to occupy an equatorial position, all of the groups on the ring must occupy axial positions. The combined steric hindrance of all the groups is more than the steric hindrance associated with one group. Therefore, the equilibrium will favor the form in which the group occupies an axial position. The structure of L-idose is: L-Idose.8. D-Allose (ompound A) β-pyranose form EtI Ag Et Et Et Et Et.8. Glucose can adopt a chair conformation in which all of the substituents on the ring occupy equatorial positions. Therefore, D-glucose can achieve a lower energy conformation than any of the other D-aldohexoses.

25 APTER.8. taut D-glucose taut taut taut taut taut L-glucose

26 APTER.8. ompound X is a D-aldohexose that can adopt a β-pyranose form with only one axial substituent. Recall that D-glucose has all substituents in equatorial positions, so compound X must be epimeric with D-glucose either at (D-mannose), (D-allose), or (D-galactose). ompound X undergoes a Wohl degradation to produce an aldopentose, which is converted into an optically active alditol when treated with sodium borohydride. Therefore, compound X cannot be D-allose, because a Wohl degradation of D-allose followed by reduction produces an optically inactive alditol. We conclude that compound X must be either D-mannose or D-galactose. The identity of compound X can be determined by treating compound X with sodium borohohydride. Reduction of D-mannose should give an optically active alditol, while reduction of D-galactose gives an optically inactive alditol..87. ompound A is a D-aldopentose. Therefore, there are four possible structures to consider (Figure.). When treated with sodium borohydride, compound A is converted into an alditol that exhibits three signals in its NMR spectrum. Therefore, compound A must be D- ribose or D-xylose both of which are reduced to give symmetrical alditols (thus, three signals for five carbon atoms). When compound A undergoes a Kiliani-Fischer synthesis, both products can be treated with nitric acid to give optically active aldaric acids. Therefore, compound A cannot be D-ribose, because when D-ribose undergoes a Kiliani-Fischer synthesis, one of the products is D-allose, which is oxidized to give an optically inactive aldaric acid. We conclude that the structure of compound A must be D-xylose. D-Xylose ompound D is expected have six signals in its NMR spectrum, while compound E is expected to have only three signals in its NMR spectrum. ompound D ompound E