5158

Chemical analysis of an aldopentose (A) gave the following information:

(a) Treatment of A with nitric acid gave optically inactive diacid, B.

(b) Ruff degradation of A gave one enantiomer of erythrose, C.

(d) Ruff degradation of C gave D-glyceraldehyde.

On the basis of this information, give structures for A, B and C. Show equations to support your structures.

5159

An aldohexose, E, undergoes nitric acid oxidation to give an optically inactive diacid. Compound E also undergoes the Ruff degradation to given an aldopentose, F. When it is oxidized with nitric acid, an optically active diacid is formed. Ruff degradation of F, followed by nitric acid oxidation gives L-tartaric acid. Give the structure for E and F and indicate your reasoning.

5161

From the following information, deduce the ring structures of the monosaccharides:

Sugar (as methyl glycoside)	Moles of HIO₄ consumed	Moles of HCO₂H formed	Moles of HCHO formed
methyl a-D-mannoside	2	1	0
methyl a-riboside	1	0	0
a methyl glycoside of an aldohexose	3	2	0
a methyl glycoside of an aldohexose	2	0	1

5255

Using structures, show how the reaction of a monsaccharide of unknown structure, L-gulose, could be used in the final step of the Fischer proof of structure of D-glucose in order to permit the distinction between D-glucose and the diastereomeric D-mannose.

5258

Using chemical equations and Fischer structures, explain why the oxidation of optically active galactose produces optically inactive galactaric acid.

D-(+)-galactose

5271

Assign structures to the aldohexoses D-(+)-galactose and D-(+)-talose on the basis of the following evidence. Show how the evidence leads you to your conclusions.

• D-(+)-galactose and D-(+)-talose yield the same osazone

• Degradation of D-(+)-galactose yields D-(-)-lyxose

• Oxidation of D-(+)-galactose by nitric acid yields an inactive meso diacid, galactaric acid (also called mucic acid).

(-)-lyxose galactaric acid

5272

Identify the glucose derivative, A, that would give the following results with HIO₄: