Write a note on the structure of fructose.

(N/A) Fructose is a ketohexose. It is obtained along with glucose by the hydrolysis of sucrose. It is a natural monosaccharide found in honey,fruits,and vegetables. The molecular formula of fructose is $C_{6}H_{12}O_{6}$. The reactions show that fructose is a six-carbon straight-chain compound with a ketonic group at carbon-$2$. It is naturally laevorotatory and belongs to the $D$-series. It is appropriately written as $D-(-)$-Fructose.
Fructose exists in two cyclic forms which are obtained by the addition of the $-OH$ group at the $C-5$ carbon to the ketonic group $(>C=O)$ at the second carbon. The ring thus formed is a five-membered ring and is named as furanose by analogy to the compound furan. Furan is a five-membered cyclic compound with one oxygen and four carbon atoms. Fructose shows mutarotation.
The Haworth structure of fructose is shown below:
(Image: $938-$s38)