Alternative definition : CRCH: A hexose with a keto group, also called a keto-hexose. Aside from the keto group,
each of the 5 remaining carbons has one hydroxyl group, in the S,R, and R configuration
counting from the first hydroxyl containing asymmetric carbon next to the ketone in
the straight chain ( Fisher) projection. All other carbons are bound to hydrogen exclusively.
Occurs mostly as furan and rarely as pyran or straight chain. When fructose forms
a ring an additional anomeric asymmetric carbon is created which is denoted as alpha
or beta. For isomers see http://en.wikipedia.org/wiki/fructose.;