Fructose is a six-carbon ketose monosaccharide with the same molecular formula as glucose, but different connectivity in the open-chain form. In aqueous chemical solution, fructose occurs mainly in cyclic forms.
Fructose supplies one of the two sugar units in sucrose and is the repeating building block of many fructans. These examples distinguish a free monosaccharide from its residues inside larger carbohydrates.[ref]
25.1 Classification of Carbohydrates. Classification of monosaccharides
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