Organic Chemistry 2 · Nitrogen and biological molecules
Carbohydrate structure and equilibria: practice problems
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- Ring closure of D-glucose to β-D-glucopyranose
- Close an aldose chain
- Activate an anomeric acetal
- Amadori rearrangement of the D-glucose–glycine imine
- 4,6-O-Benzylidene acetal of methyl α-D-glucopyranoside
- Bromine water oxidation of D-glucose to D-gluconic acid
- Oxidation of glyceraldehyde to glyceric acid with bromine water
- Acid hydrolysis of cellobiose to two D-glucose
- Glyceraldehyde to dihydroxyacetone through an enediol
Draw the mechanism 37
- Close an aldose chainForm a five-membered hemiacetal through intramolecular carbonyl addition and protonation.
- Activate an anomeric acetalShow acid activation and glycosidic cleavage without inventing direct loss of methoxide.
- Amadori rearrangement of the D-glucose–glycine imineDraw the acetic acid-catalysed Amadori rearrangement: iminium formation, loss of the C2–H to the 1,2-enaminol and tautomerization to the 1-amino-1-deoxy ketose.
- 4,6-O-Benzylidene acetal of methyl α-D-glucopyranosideDraw the ZnCl2-promoted formation of the 4,6-O-benzylidene acetal from methyl α-D-glucopyranoside and benzaldehyde, through the hemiacetal and the oxocarbenium ion.
- Bromine water oxidation of D-glucose to D-gluconic acidDraw the hydrate, hypobromite and C–H loss steps by which bromine water oxidizes C1 of D-glucose to D-gluconic acid.
- Oxidation of glyceraldehyde to glyceric acid with bromine waterDraw hydration of the glyceraldehyde aldehyde, bromination of a hydrate OH and the elimination of bromide with C–H loss that gives glyceric acid.
- Acid hydrolysis of cellobiose to two D-glucoseDraw the acid-catalysed hydrolysis of the β(1→4) glycosidic bond of cellobiose through the glucosyl oxocarbenium ion to two molecules of D-glucose.
- Glyceraldehyde to dihydroxyacetone through an enediolDraw hydroxide removing the α-hydrogen of glyceraldehyde, protonation to the enediol, deprotonation of the C2 OH and reprotonation at C1 to dihydroxyacetone.
- Ring closure of D-fructose to β-D-fructofuranoseDraw acid-catalysed hemiketal formation in which the C5 hydroxyl of D-fructose closes onto the C2 ketone to give β-D-fructofuranose.
- Ring closure of D-fructose to β-D-fructopyranoseDraw acid-catalysed hemiketal formation in which the C6 hydroxyl of D-fructose closes onto the C2 ketone to give the six-membered β-D-fructopyranose.
- Mutarotation of α-D-galactopyranose to β-D-galactopyranoseDraw the acid-catalysed ring opening of α-D-galactopyranose to the open-chain aldehyde and its reclosure on the opposite face of C1 to β-D-galactopyranose.
- Ring closure of D-galactose to β-D-galactopyranoseDraw base-catalysed hemiacetal formation: hydroxide deprotonates the C5 hydroxyl of D-galactose, the alkoxide adds to C1 and water protonates the anomeric oxygen.
- 6-O-Acetyl-β-D-glucopyranose from acetic anhydrideDraw the C6 hydroxyl of β-D-glucopyranose adding to acetic anhydride, loss of acetate from the tetrahedral intermediate and pyridine removing the proton.
- Epimerization of D-glucose to D-mannoseDraw hydroxide removing the C2 hydrogen of open-chain D-glucose and water reprotonating C2 from the opposite face to give D-mannose.
- Ring closure of D-glucose to β-D-glucopyranoseDraw the C5 hydroxyl adding to the C1 aldehyde of D-glucose and the water-relayed proton transfer that gives the β-pyranose hemiacetal.
- Kiliani–Fischer cyanohydrins from D-arabinoseDraw catalytic cyanide adding to each face of the D-arabinose aldehyde and HCN protonating each alkoxide, giving the two epimeric cyanohydrins.
- Cyanohydrin formation from D-glyceraldehyde (Kiliani–Fischer)Draw cyanide adding to the aldehyde of D-glyceraldehyde and HCN protonating the alkoxide to the new cyanohydrin stereocentre of the Kiliani–Fischer chain extension.
- Koenigs–Knorr β-methyl glucoside from acetobromoglucoseDraw the silver-promoted Koenigs–Knorr reaction of acetobromoglucose with methanol, including the C2-acetate dioxolenium ion that delivers the 1,2-trans β-glucoside.
- Acid hydrolysis of lactose to D-galactose and D-glucoseDraw the acid-catalysed hydrolysis of the β(1→4) glycosidic bond of lactose through the galactosyl oxocarbenium ion to D-galactose and D-glucose.
- Hydrolysis of maltose to two D-glucoseDraw protonation of the α(1→4) glycosidic oxygen of maltose, release of the reducing glucose unit as the oxocarbenium ion forms, water capture and deprotonation.
- Methyl α-D-mannopyranoside by Fischer glycosylationDraw the HCl-catalysed Fischer glycosylation of α-D-mannopyranose with methanol through the oxocarbenium ion to methyl α-D-mannopyranoside.
- Ring closure of D-mannose to α-D-mannopyranoseDraw acid-catalysed hemiacetal formation in which the C5 hydroxyl of D-mannose adds to the C1 aldehyde to give α-D-mannopyranose.
- Methyl α-D-glucopyranoside by Fischer glycosylationDraw protonation of the anomeric OH, loss of water to the oxocarbenium ion, methanol capture and deprotonation to methyl α-D-glucopyranoside.
- Hydrolysis of methyl β-D-glucopyranoside to D-glucoseDraw protonation of the glycosidic oxygen, loss of methanol to the oxocarbenium ion, water capture and deprotonation to β-D-glucopyranose.
- Mutarotation of β-D-glucopyranose to α-D-glucopyranoseDraw acid-catalysed opening of the β-glucopyranose ring to the protonated aldehyde and reclosure on the other face to α-D-glucopyranose.
- Reduction of D-fructose to D-glucitol and D-mannitolDraw borohydride adding to each face of the C2 ketone of D-fructose and water protonating each alkoxide, giving the epimeric alditols D-glucitol and D-mannitol.
- Reduction of D-glucose to D-glucitol (sorbitol) with NaBH4Draw hydride delivery from borohydride to the open-chain aldehyde of D-glucose and protonation of the alkoxide by water to give D-glucitol.
- Reduction of glyceraldehyde to glycerolDraw hydride delivery from borohydride to the aldehyde carbon of glyceraldehyde and protonation of the alkoxide to glycerol.
- Reduction of D-mannose to D-mannitol with NaBH4Draw the borohydride reduction of open-chain D-mannose and the acidic workup that protonates the alkoxide to give D-mannitol.
- Nitric acid oxidation of D-glucose to D-glucaric acidDraw how warm dilute nitric acid oxidizes both ends of D-glucose, through hydrates and nitrate esters, to the dicarboxylic acid D-glucaric acid.
- Glyceraldehyde phenylhydrazone, first stage of osazone formationDraw phenylhydrazine adding to the aldehyde of glyceraldehyde, the acetic acid-mediated proton transfers and loss of water to the phenylhydrazone.
- Methyl β-D-ribofuranoside by kinetic Fischer glycosylationDraw the HCl-catalysed Fischer glycosylation of β-D-ribofuranose with methanol, through the furanosyl oxocarbenium ion, to methyl β-D-ribofuranoside.
- Ring closure of D-ribose to β-D-ribofuranoseDraw acid-catalysed hemiacetal formation in which the C4 hydroxyl of D-ribose adds to the C1 aldehyde to give the five-membered β-D-ribofuranose.
- Ruff degradation of D-gluconate to D-arabinoseDraw the radical oxidative decarboxylation by which H2O2 and iron(III) shorten D-gluconate by one carbon to D-arabinose.
- Acid hydrolysis of sucrose to D-glucose and D-fructoseDraw the acid-catalysed hydrolysis of sucrose in which the fructofuranosyl oxocarbenium ion forms and water captures it, giving D-glucose and D-fructose.
- Retro-cyanohydrin step of the Wohl degradationDraw methoxide deprotonating the cyanohydrin OH of 2,3-dihydroxypropanenitrile and the alkoxide expelling cyanide to give glycolaldehyde.
- Wohl degradation: D-gluconitrile to D-arabinoseDraw the methoxide-promoted retro-cyanohydrin reaction in which D-gluconitrile loses cyanide to give D-arabinose.
Predict the product 11
- Locate the remaining reducing endPredict reducing behavior from two specified anomeric sites.
- Glucose with excess acetic anhydride and pyridinePredict the ester formed when glucose is fully acetylated.
- Bromine water oxidation of D-glucosePick the structure formed when bromine water oxidizes D-glucose.
- Permethylation of D-glucose, then acid hydrolysisPredict the result of exhaustive methylation and hydrolysis of glucose.
- Methyl glucoside from D-glucose and methanol/HClPredict the product of D-glucose with methanol and acid.
- Hydrolysis of methyl α-D-glucopyranoside in aqueous acidPredict the products of acid hydrolysis of a methyl glycoside.
- Warm nitric acid oxidation of D-glucosePredict the product of an aldose with warm nitric acid.
- Kiliani–Fischer chain extension of D-arabinosePredict the aldohexoses formed by Kiliani–Fischer synthesis from D-arabinose.
- Sodium borohydride reduction of D-glucosePredict the alditol formed by reducing an aldose.
- Benedict's test on D-glucosePredict the Benedict's test result for an aldose.
- Wohl degradation of D-glucosePredict the aldopentose formed by Wohl degradation of D-glucose.
Classify 16
- Read a Fischer projectionAssign carbon count and D/L family without inferring optical rotation.
- α or β?Assign α or β to a D-pyranose drawn as a Haworth projection.
- Cellobiose glycosidic linkageClassify the linkage between the glucose units of cellobiose.
- Monomer of chitinIdentify the repeating unit and linkage of chitin.
- Aldose or ketose?Classify monosaccharides by carbonyl type and carbon count.
- D or L?Assign D or L to a sugar from its Fischer projection.
- How 2-deoxyribose differs from riboseIdentify the structural difference between 2-deoxy-D-ribose and D-ribose.
- D- vs L-glucoseName the relationship between D- and L-glucose.
- C2 epimersName the relationship between D-glucose and D-mannose.
- Spot D-glucoseRecognize D-glucose among its stereoisomers.
- Glucose vs galactoseIdentify the relationship between D-glucose and D-galactose.
- Branch-point linkage in glycogenIdentify the glycosidic linkage at the branch points of glycogen.
- Is methyl glucoside a reducing sugar?Classify a methyl glycoside as reducing or non-reducing.
- What lactose is made ofIdentify the monosaccharides and linkage of lactose.
- Maltose glycosidic linkage and reducing behaviourClassify the linkage in maltose and whether it is reducing.
- Pyranose or furanose ring?Name a cyclic sugar from its ring size (pyranose or furanose).
Compare 2
- Compare two stereochemical changesDistinguish a non-anomeric epimer pair from an anomer pair.
- Starch versus cellulose linkageCompare the structures of starch and cellulose.
Calculate 6
- Calculate an equilibrium mixtureInfer anomer fractions from a supplied linear optical-rotation model.
- Number of aldopentose stereoisomersCount the stereoisomers of an open-chain aldopentose.
- Fructose countCount stereocentres in an open-chain ketohexose.
- Percent α-D-glucose at mutarotation equilibriumCalculate the anomer fraction of glucose at equilibrium from specific rotations.
- Specific rotation of an equilibrated D-glucose solutionCalculate specific rotation from observed rotation, concentration and path length.
- Count stereocentresCount the stereocentres in an open-chain aldohexose.
Find the error 1
- Diagnose absent mutarotationExplain why a methyl glycoside lacks neutral-water anomer equilibration.
Interpret the evidence 3
- Assign anomeric configurationUse a supplied Haworth reference instead of equating alpha with D.
- Find the anomeric carbonLocate the anomeric carbon in a cyclic sugar.
- Anomeric carbon of D-fructofuranoseLocate the anomeric carbon in the furanose form of D-fructose.
Work backward 1
- Recover the ring-forming atomsIdentify anomeric carbon and ring size for ketose cyclization.
Plan a synthesis 1
- Choose an equilibration strategyConnect glycoside hydrolysis with restoration of anomer exchange.
Explain why 2
- What mutarotation meansExplain mutarotation as α/β anomer interconversion through the open-chain form.
- Why sucrose is a non-reducing sugarExplain why sucrose gives a negative reducing-sugar test.
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