Aldose-ketose isomerism
We have already seen that in a monosaccharide either an aldehyde (-€HO) or a ketone (>C=O) group is present. The former is called as aldose while the latter is known as ketose. Glucose and fructose both have the formula C6H12 06 but glucose is an aldohexose (aldehyde bearing hexose) and fructose is a ketohexose (ketone bearing hexose), so they are isomers to one another.