The beta (β) Fructose molecule - rotatable in 3 dimensions

Fructose (fruit sugar) is a monosaccharide - formula C6H12O6.
It shares the same empirical formula with other 6-carbon (hexose) sugars such as glucose and galactose.

6 carbon atoms (grey) form the backbone of the molecule, and in this version of the fructose molecule the middle 4 carbons form into a 5 sided ring with one oxygen atom (red) in the ring. Label / unlabel Carbon numbers

The hydrogen atoms (white) are either attached directly to the carbons, or via oxygen as -OH groups - at an angle.
Only the two carbons outside the ring (C1 & C6) have 2 single hydrogens and an -OH group. C5 has a single hydrogen atom only.

The molecule shown is the beta- (β) form, as the -OH group on C2 projects above the ring. Thus it projects to the left as the molecule is rotated to show the ring edge-on ... return to face view. In fact the beta form is much more common.

This form of fructose molecule is also known as fructofuranose, as the central part of the molecule is similar to furan, a five-membered ring-shaped compound with four carbon atoms and one oxygen. In solution fructofuranose is in equilibrium with (over 3x as much) of the (sweeter) fructopyranose form (similar to glucose) as well as smaller amounts of open-chain (stick-like) fructose. However it is conventional to show the furanose form, as this is seen in derived compounds such as sucrose (disaccharide), nystose (fructo-oligosaccharide) and inulin (polysaccharide).

This is in equilibrium with other forms, including an open-chain form which has a >C=O ketone group at Carbon 2 which gives it reducing properties, so that it reacts with reagents such as Benedict's.

Label/ Unlabel atoms

Web references

Fructose From Wikipedia, the free encyclopedia