Structure Determination of D-Fructose
Structure Determination of Open Chain D-Fructose
The structure of fructose has been derived from a the following facts and conclusions which are given below-1. Elemental analysis and molecular weight determination show that the molecular formula of fructose is C6H12O6.
2. Complete reduction of fructose with concentrated hydriodic acid in the presence of red phosphorous produces n-hexane as the major product. This indicates that the six carbon atoms in the fructose molecule form a straight chain.
3. Fructose readily dissolves in water to give a neutral solution. This indicates that the fructose molecule does not contain a carboxyl group.
4. Fructose reacts with acetic anhydride in the presence of pyridine to form a pentaacetate. This reaction indicates the presence of five hydroxyl groups in a fructose molecule. Since fructose is a stable compound, the five hydroxyl groups must be present on separate carbon atoms.
5. Fructose reacts with hydroxylamine to form a monoxime, or adds only one moole of HCN to give a cyanohydrin. These reactions indicate the presence of either an aldehydic (-CHO) or a ketonic >C=O group, but not both.
6. Oxidation of fructose with concentrated nitric acid yields a mixture of glycollic acid and tartaric acid. Since this oxidation occurs with the breaking of the carbon chain, the carbonyl group must be present as a ketone group.
7. Partial reduction of fructose with sodium amalgam and water produces a mixture of two epimeric alcohols, sorbitol and mannitol, because a new asymmetric centre has been created at C-2. This confirms the presence of a ketonic group.
8. When fructose is treated with HCN, it forms an addition product which upon hydrolysis and subsquent reduction with hydroidic acid and red phosphorus gives 2-methyl hexanoic acid. This indicates that the keto group is adjacent to one of the terminal carbon atoms.
9. From the above evidences we conclude that the Fructose is a pentahydroxy hexanone and can be represented as follows-
