Cyclic structure of Fructose 

Like glucose, fructose also has a cyclic structure. Since fructose contains a keto group, it forms an intramolecular hemiketal. In the hemiketal formation, C₅– OH of the fructose combines with C₂-keto group. As a result, C₂ becomes chiral and thus has two possible arrangements of CH₂OH and OH group around it. Thus, D-fructose exists in two stereoisomeric forms, i.e., α-D-fructopyranose and β-D fructopyranose. However in the combined state (such as sucrose), fructose exists in furanose form as shown below: