91Ó°ÊÓ

Calculate the percentages of $\mathbf{Î\pm }$-d-glucose and $\mathbf{β}$-d-glucose present at equilibrium from the specific rotations of $\mathbf{Î\pm }$-d-glucose, $\mathbf{β}$-d-glucose, and the equilibrium mixture. Compare your values with those given in Section 20.10.

The specific rotation of $\mathbf{Î\pm }$-d-galactose is 150.7 and that of b-d-galactose is 52.8. When an aqueous mixture that was initially 70% $\mathbf{Î\pm }$-d-galactose and 30% $\mathbf{β}$-d-galactose reaches equilibrium, the specific rotation is 80.2. What is the percentage of $\mathbf{Î\pm }$-d-galactose and $\mathbf{β}$-d galactose at equilibrium?

Draw the mechanism for the dehydration step in the Wohl degradation

An unknown disaccharide gives a positive Tollens’ test. A glycosidase hydrolyzes it to d-galactose and d-mannose. When the disaccharide is treated with methyl iodide and ${\mathbf{Ag}}_2\mathbf{O}$ and then hydrolyzed with dilute HCl, the products are 2,3,4,6-tetra-O-methylgalactose and 2,3,4-tri-O-methylmannose. Proposea structure for the disaccharide.

Predict whether d-altrose exists preferentially as a pyranose or a furanose.

Predict whether d-altrose exists preferentially as a pyranose or a furanose. (Hint:In the most stable arrangement for a five-membered ring, all the adjacent substituents are trans.)

What are the systematic names of the following compounds? Indicate the configuration (R or S) of each asymmetric center.a. D-glucose b. D-mannose c. D-galactosed. L-glucose

Trehalose, ${\mathbf{C}}_{12}{\mathbf{H}}_{22}{\mathbf{O}}_{11}$, is a nonreducing sugar that is only 45% as sweet as sugar. When hydrolyzed by aqueous acid or the enzyme maltase, it forms only D-glucose. When it is treated with excess methyl iodide in the presence of Ag2O and then hydrolyzed with water under acidic conditions, only2,3,4,6-tetra-O-methyl-d-glucose is formed. Draw the structure of trehalose.

Trehalose, C₁₂H₂₂O₁₁, is a nonreducing sugar that is only 45% as sweet as sugar. When hydrolyzed by aqueous acid or the enzyme maltase, it forms

only D-glucose. When it is treated with excess methyl iodide in the presence of Ag2O and then hydrolyzed with water under acidic conditions, only

2,3,4,6-tetra-O-methyl-d-glucose is formed. Draw the structure of trehalose.

What sugar is the C-3 epimer of D-fructose?