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.

When a pyranose is in the chair conformation in which the CH2OH group and the C-1 OH group are both in axial positions, the two groups can react to form an acetal. This is called the anhydro form of the sugar (it has 'lost water'). The anhydro form of d-idose is shown here. Explain why about 80% of d-idose exists in the anhydro form in an aqueous solution at 100 °C, but only about 0.1% of d-glucose exists in the anhydro form under the same conditions.

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 Ag2O and then hydrolyzed with dilute HCl, the products are 2,3,4,6-tetra-O-methylgalactose and 2,3,4-tri-O-methylmannose. Propose a structure for the disaccharide.

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.)

Propose a mechanism for the rearrangement that converts an ⍺-hydroxyimine to an ⍺-aminoketone in the presence of a trace amount of acid.

Draw the mechanism for the elimination step in the Wohl degredation.