Fructose (fruit sugar) is a monosaccharide - formula C6
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
oxygen atom (red)
in the ring.
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
on C2 projects above the ring.
Thus it projects to the left as the molecule is
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.