Structural Insights into D-Fructose: Chemistry Department Findings

Exploring the structural aspects of D-fructose, this content delves into the open chain structure limitations, pyranose and furanose structures, ring size determination, and Haworth projection formulae. Discover how the cyclic hemiketal structures resolve the shortcomings of the open chain representation and provide a deeper understanding of D-fructose's properties and reactivity.

• Fructose Chemistry
• Structural Insights
• Pyranose Structure
• Furanose Structure
• Haworth Projection

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1. DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 1

2. RING STRUCTURE OF D-(-)-FRUCTOSE Limitations of the Open Chain Structure of Fructose Pyranose Structure of D-(-)-Fructose Ring Size of D-(-)-Fructose Haworth Projection Formulae 2 DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB

3. Limitations of the Open Chain Structure of Fructose The open chain structure of fructose accounts for most of its properties but fails to explain the following facts: D-Fructose does not react with sodium bisulphite even though it contains a ketonic group. It exists in two stereoisomeric farms, i.e., -D-(-)-fructose and - D-(-)-fructose which show mutarotation. It forms two stereoisomeric methyl fructosides on treatment with methanol and dry HCl gas. DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 3

4. Pyranose Structure of D-(-)-Fructose To explain limitations of open chain structure and certain other facts of D-fructose, it was suggested that fructose exists in a cyclic hemiketal structure. It was assigned a six- membered hemiketal or pyranose structure which is formed by combination of ketonic group at C-2 and hydroxyl group at C-6 to give rise to - and -D-fructose as shown below DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 4

5. Ring Size of D-(-)-Fructose The procedure used for determining the ring size of fructose was similar to that in case of glucose, but fructose derivative (IV) is first oxidised with dil. HNO3 and then with KMnO4. By doing so Iactone (VI) is obtained which upon oxidation with moderately conc. HNO3 gave D-arabinotrimethylglutartc acid. This confirmed six- membered or pyranose ring of fructose. DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 5

6. DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 6

7. Haworth Projection Formulae The Haworth projection formulae of - and -D-fructopyranose may be represented as follows DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 7

8. Furanose Structure of D-(-)-Fructose Although in the free state fructose has the six-membered cyclic or the pyranose structure but in the combined state such as in fructosides, disaccharides like sucrose, etc., fructose always has the five-membered cyclic ring structure or the furanose structure. The Fischer and Haworth projection formulae for - and -D-fructofuranose are given below DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 8

9. Conformations of - and -D-(-)-Fructose Like glucose, fructose also exists in the chair conformation. The chair conformations of - and -D-(-)-Fructoses are given below DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 9

10. Structure of Disaccharides Sucrose Maltose Lactose DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 10

11. DEPARTMENT OF CHEMISTRY GC PAONTA SAHIB 11