ABSTRACT
Most of the carbohydrates discussed in this chapter are polyhydroxylated aldehydes or ketones, although there are other polyhydroxylated derivatives. ˜ere are two fundamental ways to
classify carbohydrates. ˜e rst is based on the type of functional group that accompanies the hydroxyl units. ˜e second is based on the number individual units that make up the carbohydrate. Carbohydrates are classied by the nature of the functional groups X1 and X2. In a carbohydrate, there are several repeating CHOH units dened by the integer “n,” where n = 3, 5, or 6, and so on. For example, when n = 3 in a carbohydrate, the structure is X1-CHOH-CHOHCHOH-X2. Most carbohydrates are dened by making X1 and/or X2 = CH2OH, CHO, COR (a ketone), or COOH. A glycose has a CH2OH and an aldehyde or ketone unit and a glycitol has two CH2OH units (sometimes called an alditol). When one group is a carboxylic acid and the other is CH2OH, it is a glyconic acid (sometimes called an aldonic acid). A glycaric acid has two carboxyl units and is a hydroxy-dioic acid (sometimes called an aldaric acid), and a uronic acid has a carboxyl group and an aldehyde group.
