Tiêu đề Exercises-for-the-unit-2_Carbohydrates ✅

Unit 2 Carbohydrates 1. Sugar Alcohols In the monosaccharide derivatives known as sugar alcohols, the carbonyl oxygen is reduced to a hydroxyl group. For example, D-glyceraldehyde can be reduced to glycerol. However, this sugar alcohol is no longer designated D or L. Why? 2. Configuration and Conformation Which bond(s) in α-D-glucose must be broken to change its configuration to β-D-glucose? Which bond(s) to convert D-glucose to D-mannose? 3. Melting Points of Monosaccharide Osazone Derivatives Many carbohydrates react with phenylhydrazine (C6H5NHNH2) to form bright yellow crystalline derivatives known as osazones: The melting temperatures of these derivatives are easily determined and are characteristic for each osazone. This information was used to help identify monosaccharides before the development of HPLC or gas-liquid chromatography. Listed below are the melting points (MPs) of some aldose-osazone derivatives: As the table shows, certain pairs of derivatives have the same melting points, although the underivatized monosaccharides do not. Why do glucose and mannose, and similarly galactose and talose, form osazone derivatives with the same melting points? 4. Identifying Reducing Sugars Is N-acetyl-β-D-glucosamine a reducing sugar? What about D-gluconate? Is the disaccharide GlcN(α1↔1α)Glc a reducing sugar?