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Fructose

Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is often bonded to glucose to form the disaccharide sucrose. Fructose is found in honey, tree and vine fruits, flowers, berries and most root vegetables. It is absorbed directly into the bloodstream during digestion.

Fructose has the chemical formula, C 6, H 12, O 6. In the straight chain form, the carbons can be numbered from 1 to 6 from top to bottom. One O H group is attached to each of the carbons from carbons 3 to 6, and also carbon 1. Carbon 2 is a carbonyl, so the carbon is double bonded to an oxygen. To form the ring form, the O H group at carbon 5 can react with the carbonyl group. The electrons move from the oxygen in the O H group to carbon 2, and then the electrons in the carbonyl double bond move up to the oxygen. After this step proton transfer occurs to get to the final ring structure. The 5-membered ring form of fructose is made of carbons 2 to 5, with oxygen between carbon 2 and carbon 5. The oxygen in the ring came from the O H group at carbon 5. The new O H group at carbon 2 is made from the oxygen that was in the carbonyl, and the hydrogen from the O H group at carbon 5.

Figure 1: The most common isoform of fructose is a five-membered ring.

Referred from:

Article
Disaccharides
Article
Sucrose