Department of Chemistry Government College Paonta Sahib HP 1 CHEMISTRY DEPTT GC PAONTA SAHIB 2 Todays Topics Limitations of the Open Chain Structure of Fructose ID: 1048681
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1. CARBOHYDRATESChemistry: CHEM 201THDepartment of Chemistry Government CollegePaonta Sahib (HP)1CHEMISTRY DEPTT GC PAONTA SAHIB
2. 2Today’s TopicsLimitations of the Open Chain Structure of FructosePyranose Structure of D-(-)-FructoseRing Size of D-(-)-FructoseHaworth Projection FormulaeRING STRUCTURE OF D-(-)-FRUCTOSECHEMISTRY DEPTT GC PAONTA SAHIB
3. 3Limitations of the Open Chain Structure of FructoseThe 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., α-D-(-)-fructose and β-D-(-)-fructose which show mutarotation.It forms two stereoisomeric methyl fructosides on treatment with methanol and dry HCl gas. CHEMISTRY DEPTT GC PAONTA SAHIB
4. 4Pyranose Structure of D-(-)-FructoseTo 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 α- and β-D-fructose as shown belowCHEMISTRY DEPTT GC PAONTA SAHIB
5. 5Ring Size of D-(-)-FructoseThe 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.CHEMISTRY DEPTT GC PAONTA SAHIB
6. 6CHEMISTRY DEPTT GC PAONTA SAHIB
7. 7Haworth Projection FormulaeThe Haworth projection formulae of α- and β-D-fructopyranose may be represented as followsCHEMISTRY DEPTT GC PAONTA SAHIB
8. 8Furanose Structure of D-(-)-FructoseAlthough 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 α- and β-D-fructofuranose are given belowCHEMISTRY DEPTT GC PAONTA SAHIB
9. 9Conformations of α- and β-D-(-)-FructoseLike glucose, fructose also exists in the chair conformation. The chair conformations of α- and β-D-(-)-Fructoses are given belowCHEMISTRY DEPTT GC PAONTA SAHIB
10. 10Next LectureStructure of DisaccharidesSucroseMaltoseLactoseCHEMISTRY DEPTT GC PAONTA SAHIB
11. Thank You11CHEMISTRY DEPTT GC PAONTA SAHIB