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Chapter 31: Problem 710

(a) A certain sugar and its methyl glycoside can be isolated in both \(\alpha-\) and \(\beta\) -anomeric forms. Also, the ring structure of the glycoside is known to be present in the pyranose form. How could you ascertain from rotation data whether or not the parent sugar also exists in the pyranose form? (b) A D-glucose derivative with a 1,2 -epoxide ring gives a methy, \(\beta\) -D-glucoside on solvolysis with methanol. Explain how this reaction helps to establish the configuration of the \(\alpha-\) and \(\beta\) -anomers of D-glucose.

Short Answer

Expert verified
To ascertain whether the parent sugar exists in the pyranose form, compare the parent sugar's specific rotation with that of its methyl glycoside in the α- and β-anomeric forms. If they match, the parent sugar exists in the pyranose form. To establish the configuration of the α- and β-anomers of D-glucose, analyze the reaction between the epoxide ring and methanol. Since the reaction forms methyl β-D-glucoside, the opening of the epoxide ring occurs at the β-anomer position, differentiating the configurations of α- and β-anomers of D-glucose.

Step by step solution

01

Understanding pyranose structure

Pyranose is a term used to describe cyclic carbohydrate structures that resemble pyran. In such structures, the sugar has a ring of six atoms. A possibility to ascertain pyranose form is by comparing rotation data.
02

Comparing rotation data

In the given problem, assuming the parent sugar and its methyl glycoside are in equilibrium, the rotation data should match. If the specific rotation of the parent sugar matches the rotation data of its methyl glycoside in the α- or β-anomeric form, we can conclude that the parent sugar also exists in the pyranose form. Otherwise, it would not match. #b) Establishing the configuration of α- and β-anomers of D-glucose #
03

Understanding the reaction

The given D-glucose derivative has a 1,2-epoxide ring and forms methyl β-D-glucoside on solvolysis with methanol. We need to analyze how this reaction helps in identifying the configuration of the α- and β-anomers of D-glucose.
04

Relationship between the reactant and product

As the reaction proceeds, the 1,2-epoxide ring opens up and forms a methyl glycoside. Since it forms methyl β-D-glucoside, it indicates that the opening of the epoxide ring occurs at the β-anomer position, which leads to the formation of a β-D-glucoside.
05

Establishing the configuration

From the given reaction, we can tell that the 1,2-epoxide ring opens up specifically at the β-anomer position, resulting in the formation of methyl β-D-glucoside. This information helps us conclude that the α- and β-anomers of D-glucose can be differentiated based on which carbon is nucleophilically attacked during the reaction with methanol, confirming their different configurations.

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Most popular questions from this chapter

Will 2-deoxyribose form an osazone? Why?

D-Arabinose and D-ribose give the same phenylosazone. D-Ribose is reduced to the optically inactive penta- hydric alcohol, ribitol. D-Arabinose can be degraded by the Ruff method, which involves the following reactions: The tetrose, D-erythrose, so obtained can be oxidized with nitric acid to mesotartaric acid. What are the configurations of D-arabinose, D-ribose, ribitol, and D-erythrose?

When methyl \(\alpha-\mathrm{D}-\) glucoside was treated with \(\mathrm{HIO}_{4}\), it yielded 1 mole of formic acid, plus a product (A). Write the structure of \(\mathrm{A}\). When a methyl glycoside of unknown structure (B) was similarly treated with \(\mathrm{HIO}_{4}\), only 1 mole of \(\mathrm{HIO}_{4}\), was consumed, and no formic acid was produced, but the same product (A) was obtained. Draw the configurational structure of \(\mathrm{B}\).

How can the D-glucoside units of cellulose produce a polymer with a stronger, more compact physical structure than the D-glucose units of starch?

D-Raffinose is a trisaccharide that does not react with Fehling's solution. Upon hydrolysis it produces \(\mathrm{D}\) - glucose, D-galactose, and D-fructose. Completely methylated raffinose is hydrolyzed to \(2,3,4-\) tri- O -methylglucose, \(1,3,4,6-\) tetra-O-methylfrueto se, and \(2,3,4,6-\) tetra- \(\mathrm{O}-\) methylgalactose. What structures for raffinose are consistent with these data? What further information, if any, is required to identify completely the structure of raffinose?
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