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Practice Problems on Carbohydrates

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Practice Problems on Carbohydrates Carbohydrates.1 Practice Problems on Carbohydrates 1. Which one of the following is a heptulose? CH2OH C O H O H HO C H H OH H OH A B H C OH H OCHO H C OH OH H H H CH2OH OH O H H D H C HO H OH H OH CH2OH O H HO CH2OH H OH H H HO H HO OH OH H H H CH2OH O HO H E H HO CH2OH OH H HO 2. Based on the names, which one of the following does NOT have an aldehyde? A) Idose B) Tagose C) Fucose D) Sedoheptulose E) Cellobiose 3. Which formula correctly represents a simple monosaccharide? A) C5H5O5 B) C5H5O10 C) C4H8O4 D) C6H10O6 E) C4H12O6 Carbohydrates.2 4. Which one of the following structures correctly represents -D-altropyranose? H HO H CH2OH O CH2OH O CH2OH O HO HO OH H H H H H OH H H OH H HO OH OH OH H HO H HO H H H A B C H H CH2OH O CH2OH O HO HO OH H H H OH HO H H H OH H OH HO H D E 5. Which one of the following is not an aldose? H CH OH OH OH A 2 B C OH OH HO HO H OH HO O H H H O H CH2 H CH 2 H CH2 HO O H H D CH2OH E OH H H HO O HO O HO H H OH HO H H H H OH HO H 6. Which one of the following is a ketohexose? OH OH CH2OH CH2OH OH OH CH2OH A B OH D HO OH C O OH OH OH O O HO O O HOCH2 OH OH CH2OH CH2OH OH E OH HO CH2OH OH O Carbohydrates.3 7. Which one of the following compounds is a glycoside? O O H C CH H H 3 C CH2O CH OH O CH2OH O 2 O CH3 O HO O H H H C B H H OH H H CH3 O A HO OH O OH C O OH OCH H 3 O H3C C H H H H H O H CH3 CH2OH O CH2 HO CH3 H H D O O E H HO OCH2 O H OH H OH CH3O H H CH O H 2 H 8. Which one of the following structures correctly represents -L-galactopyranose? HO OH CH OH CH2OH 2 O O HO OH OH HO HO A OH B OH HO OH CH OH O O 2 O HO OH HO OH HO OH OH HO CH2OH CH2OH OH C D E 9. How many hexoses (aldohexoses and 2-ketohexoses) are possible? A) 8 B) 12 C) 16 D) 24 E) 46 Carbohydrates.4 10. Which one of the following compounds is not a glycoside? OH HO B CH2OH A O O O OH HO COO HO OCH3 OH NH2 CH3 CH2 D CH OH O HO 2 COOH C CH2 CHO O O O HO COO NH HO CO OH O CH3 OH E CH2OH O HO + Cl HO O O OH HO OH 11. Which one of the following molecules is most likely to form a cyclic hemiacetal in neutral solution? HC O A HC O B C HC O D HC O H C OH H C OH H C OH H C OCH3 H CH H COH H CO H COCH2 CH3 H CH H CO O CH H CH CH2 H2C C H COCH3 H CO H CH H COH CH3 CH OH CH2OH 2 CH2O CH2O CO E HC O CH3 H C O CH2 H COH CH3O CH H COCOCH3 CH2O Carbohydrates.5 12. Which one of the following is a ketose? CH OH 2 H OH CH2OH CH2OH OH H CH2OH CH2OH O H OH OH O O H HO H H H H H H OH H H HO HO O OH H H H H H O H HO OH HO H O H H H H OH CH2OH OH H OH H CH2OH A B C D E 13. Which one of the following compounds is a glycoside? O HN O N HO HO O HO O O O HO O OCH3 OH HO H3CO OH OH OCH3 ABC OH OCH OH 3 O H CO O 3 OCH3 OH H3CO OH OCH3 D E 14. Peonin (shown below) is a red pigment found in the petals of peony flowers. Which monosaccharide(s) would be produced by acid hydrolysis of peonin? OCH3 OH O H H H OH CH2OH O HO OH HO O H O H H O CH2OH HO II OH H H H H I A) D-glucose and D-mannose B) L-glucose and D-mannose C) D-glucose and D-galactose D) D-glucose only E) L-galactose only Carbohydrates.6 15. Referring to the previous question, what is the stereochemistry of the two glycosidic bonds denoted by I and II? A) I: and II: B) I: and II: C) I: and II: D) I: and II: 16. Which one of the following statements is NOT correct? A) D-Glucose and D-gulose have the same configuration at the penultimate carbon but different configurations at carbon 4. B) D-Glucose and D-gulose are diastereomers, but D-glucose and L-glucose are enantiomers. C) D-Gulose and D-glyceraldehyde have the same configuration at the penultimate carbon. D) D-Glucose and D-gulose both must be dextrorotatory because they are both D sugars. E) D-Glyceraldehyde is dextrorotatory, and L-glyceraldehyde is levorotatory. 17. Which of the following statements about D-2-deoxyribose (the monosaccharide in DNA) is/are most likely to be correct? a. it can exist as two furanose anomers b. it can exist as two pyranose anomers c. reaction of it with NaBH4 gives an optically inactive product A) b only B) c only C) a and b only D) a and c only E) all three statements are correct Carbohydrates.7 18. Which one of the following would show mutarotation when dissolved in water? a)OH b) OH H O H O H H O H OHH OH H HO HO OCH3 H OH H OH c) OH d) OH e) CHO O H O H H H H H H OH OH OHH OH H OH HO O OH HO O H H OH O H H OH H OH H OH OHH H O H OH H H OH 19. Consider the equilibrium shown below; the optical rotation values are given for each of the cyclic molecules. Which one of the following statements is true? HO HO HO CH2OH O CH2OH OH CH2OH O OH HO HO O HO OH OH OH H OH [ ]D25 = +20 [ ]D25 = +110 A) The and anomers are enantiomers, related by inversion of stereochemistry at C1. B) The process of interconversion is termed racemization C) The acyclic intermediate is achiral D) The and anomers are diastereomers E) Mutarotation occurs for aldose monosaccharides only Carbohydrates.8 20. A student dissolved -D-galactose in acid, placed the solution in a sealed tube, and then monitored the optical activity of the solution in a polarimeter over time. Which statement best explains the data collected below? 160 140 120 100 80 60 036912 Time (hours) A) A portion of the -D-galactose was converted to -D-fructose B) A portion of the -D-galactose was hydrolyzed to two smaller sugars C) A portion of the -D-galactose was converted to -D-glucose D) The solution of -D-galactose evaporated over time E) -D-galactose formed an equilibrium mixture with -D-galactose 21. Which one of the following statements is not correct? A) Individual units of sugars are typically linked by O-glycoside bonds to form oligomers and polymers. B) In the acid-catalyzed formation of a hemiacetal from an aldehyde and an alcohol, the carbonyl group is protonated to make it better nucleophile. C) Acetals are resistant to alkaline (basic) conditions. D) Hemiacetals readily revert to their aldehyde and alcohol components under neutral, acidic, or basic conditions. E) Bases of nucleic acids are linked to sugars via N-glycoside bonds. Carbohydrates.9 22. Bromine water can be used to oxidize aldoses to aldonic acids. What is the reduction product formed in this reaction? A) HBrO3 + B) Br3 C) HBr D) HOBr E) Br2 23. Which one of the following compounds can be readily oxidized by Br2/H2O? H a) H OH c) H OH e) HO OH OH HO H HO OH H OH H H O O H O OH H O OH b) OH d) H OH H O OH OH H OHH OH HO OH HO H OH H OH 24. The oxidation of D-talose by nitric acid gives the same optically active diacid as the oxidation of which other sugar? A) L-Talose B) L-Altrose C) D-Galactose D) D-Altrose E) L-Gulose 25. D-Arabinose is converted by nitric acid into the same aldaric acid as that obtained from the reaction of which other sugar with nitric acid? A) L-ribose B) L-xylose C) D-xylose D) D-lyxose E) D-ribose Carbohydrates.10 26. Reduction of D-ribulose with NaBH4 forms equal amounts of two products, Y and Z, i.e. 50% yield of each. Product Y does not rotate plane-polarized light. Similar reduction of which one of the following sugars would give product Z in 100% yield? A) D-xylose B) D-xyulose C) D-glucose D) D-lyxose E) D-ribose 27.
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