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Stereoisomers are compounds that only differ in the orientation of functional groups when the molecule is placed in three-dimensional space. These orientations are represented using absolute configurations.

In molecules containing more than one chiral centre, the configuration of each chiral centre is determined separately. The isomers that differ in configuration at only one chiral centre are called epimers.

The systematic name of fructose is (3S,4R,5R)-1,3,4,5,6-pentahydroxyhexan-2-one. It has six carbon atoms. Therefore is a hexose. The presence of the ketone group in the second position makes it a ketose.

Therefore, fructose is a ketohexose. It contains five hydroxyl groups. The third, fourth and fifth carbon atoms are chiral centres.

The chemical formula of fructose is C₆H₁₂O₆ , and it is a simple sugar.

The stereoisomer of fructose in which the chiral carbon farthest to the ketone functional group has the hydroxyl group positioned to the right side is D-fructose.

Its structure is given by:

D-fructose

The C-3 epimer of D-fructose will have a different configuration at the third carbon atom, and the configuration of all the other chiral centres will be the same.

Therefore, the structure of the C-3 epimer can be given as:

C-3 epimer of D-fructose

The above structure represents the D isomer of Psicose sugar. Therefore, the C-3 epimer of D-fructose is D-Psicose