Concept explainers
Interpretation:
The series of
Concept introduction:
舧 Formation of isomers is called isomerization. Monosaccharides undergo a series of keto-enol tautomerizations and enolizations and to produce different isomeric forms. In order to preserve the stereochemical nature of the compounds, the formation of such isomeric forms needs to be prevented.
舧 Stereochemistry: A carbon atom is attached to four distinct groups is said to be a stereogenic or chirality center of that molecule. A stereocenter is that point in a molecule where any two groups exchange their positions to form stereoisomers.
舧 The pair of diastereomers that shows different configuration at the chirality center are called epimers. The aldohexoses,
舧 A carbohydrate is a
舧
舧 Carbohydrates are oxidized by
舧 Aldaric acids are carbohydrates having two
舧 Monosaccharides containing six carbon atoms and an
舧 Alditols are compounds produced from aldoses or ketoses on reduction with certain reagents such as sodium borohydride (
舧 Compounds formed by the reaction of reducing sugars with excess of phenyl hydrazine are called osazones. Osazones are products of oxidation and are produced by all reducing sugars.
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舧 Fischer projection is a way of representing the structural formulae of compounds through cross formulation of their open chain structures.
舧 Bromine water is an effective reagent that selectively oxidizes the
舧 While dissolved in aqueous bases such as pyridine, monosaccharides undergo complex isomerization as they form different enols and keto-enols. Aldonic acids form epimers (usually at the
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Organic Chemistry
- Kojibiose is a reducing sugar that forms D-glucose on hydrolysis with aqueous acid. Reaction of kojibiose with iodomethane and Ag20 yields an octamethyl derivative, which can be hydrolyzed with aqueous acid to give one equivalent of 2,3,4,6-tetra-O- methyl-D-glucopyranose and one equivalent of 3,4,6-tri-O-methyl-D-glucopyranose. If kojibiose is hydrolyzed by alpha-glucosidases but not beta-glucosidases, what is its structure?arrow_forwardA D-aldopentose A is oxidized to an optically inactive aldaric acid with HNO3. A is formed by the Kiliani–Fischer synthesis of a D-aldotetrose B, which is also oxidized to an optically inactive aldaric acid with HNO3. What are the structures of A and B?arrow_forwardd-Xylose and d-lyxose are formed when d-threose undergoes a Kiliani–Fischer synthesis. d-Xylose is oxidized to an optically inactive aldaric acid,whereas d-lyxose forms an optically active aldaric acid. What are the structures of d-xylose and d-lyxose?arrow_forward
- A D-aldohexose A is formed from an aldopentose B by the Kiliani-Fischer synthesis. Reduction of A with NABH4 forms an optically inactive alditol. Oxidation of B forms an optically active aldaric acid. What are the structures of A and B?arrow_forwardRegarding 4-O- (α-D-psychofuranosyl) -β-D-allopyranose. Please indicate the RIGHT alternative: (a) The disaccharide reacts with CH3OH in an acid medium to form a glycoside that cannot be oxidized with HNO3. (b) It is a reducing disaccharide only in basic medium. (c) In the structure there is only one glycosidic bond that is of the type β 1-O-4 ' (d) The hydrolysis products of this disaccharide do not show mutarrotation. (e) The disaccharide structure contains two six-membered rings.arrow_forward(d) Draw the structure of the expected product when monosaccharide B undergo mutarotation upon dissolving in water in the presence of Tollens reagent (AGNO3, NHẠOH). он OH O. OH OH OH monosaccharide Barrow_forward
- Draw the structure of alpha-d-glucopyranose in straight chain cyclic, Haworth and cyclohexane-chair format. Draw the structures of two aldohexoses which are diastereomers but not epimersarrow_forwardEmil Fischer synthesized l-gulose, an unusual aldohexose that reduces to give d-glucitol.Suggest a structure for this l sugar, and show how l-gulose gives the same alditol asd-glucose. (Hint: d-Glucitol has ¬CH2OH groups at both ends. Either of these primaryalcohol groups might have come from reduction of an aldehyde.)arrow_forward(a) Which of the d-aldopentoses will give optically active aldaric acids on oxidation with HNO3 ?(b) Which of the d-aldotetroses will give optically active aldaric acids on oxidation with HNO3 ?(c) Sugar X is known to be a d-aldohexose. On oxidation with HNO3, X gives an optically inactive aldaric acid. WhenX is degraded to an aldopentose, oxidation of the aldopentose gives an optically active aldaric acid. Determine thestructure of X.(d) Even though sugar X gives an optically inactive aldaric acid, the pentose formed by degradation gives an opticallyactive aldaric acid. Does this finding contradict the principle that optically inactive reagents cannot form opticallyactive products?(e) Show what product results if the aldopentose formed from degradation of X is further degraded to an aldotetrose.Does HNO3 oxidize this aldotetrose to an optically active aldaric acid?arrow_forward
- If lactose is first hydrolyzed (by addition of sulfuric acid) into its constituent monosaccharide, and then subjected to complete methylation, what methylated products do you expect?arrow_forwardA D-aldopentose A is reduced to an optically active alditol. Upon Kiliani–Fischer synthesis, A is converted to two D-aldohexoses, B and C. B is oxidized to an optically inactive aldaric acid. C is oxidized to an optically active aldaric acid. What are the structures of A–C?arrow_forwardWhat is the product of the starting material D-glyceraldehyde which will (1) produce aldaric acid upon reacting with HNO3 + H2O, NaOCH2, NH2OH, and (CH3CO)2O + NaOCOCH3 (2) produce tartaric acid upon reacting with HNO3 + H2O, NaOCH3, NH2OH, and (CH3CO)2O + NaOCOCH3arrow_forward
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