Also the cyclic form can exist in boat or chair form. Chair is favored. Some monosaccharides form 5 member oxygen heterocycles called furanoses because they resemble furan. Ribose and fructose. Mutarotation is evidence for the equilibrium that exists between and anomers and the linear free aldehyde form of the sugar.
Substitution reactions result in the replacement of an O with a N or another atom.
Other amino sugars exist as well as their acetyl derivatives. Reducing sugars donate electrons to reduce other substances. When this occurs the sugar undergoes oxidation. Any sugar with a free or potentially free aldehyde group is a reducing sugar. 2 O is a red ppt.