![]() If we look at the corresponding location in the monosaccharide and ask what the functional group might be, we see that it is a hemiacetal. The carbon and these oxygens are in an acetal linkage. The atom above it is connected to two oxygens, both of which are in ether-type situations. ![]() Look at the disaccharide and focus on the oxygen which links the two rings together. Beyond that, though, there's another important structural feature. The difference between a monosaccharide and a disaccharide can be seen in the following example:Ī quick glance tells us that a monosaccharide has just one ring, a disaccharide has two, and a polysaccharide has many. We'll look at them in more detail next time. Their formulas can be be expressed as C n(H 2O) n-1. More complex carbohydrates such as starch and cellulose are polymers of glucose. For example, glucose has the formula C 6(H 2O) 6 and sucrose (table sugar) has the formula C 6(H 2O) 11. As the name implies, a carbohydrate is a molecule whose molecular formula can be expressed in terms of just carbon and water. Sugars are small molecules which belong to the class of carbohydrates. Β form: The configuration of a cyclic monosaccharide where the oxygen attached to the anomeric carbon is on the same side of the ring as the CH₂ OH group.\) Α form: The configuration of a cyclic monosaccharide where the oxygen attached to the anomeric carbon is on the opposite side of the ring from the CH₂ OH group. Stereoisomers or optical isomers: Molecules that differ three-dimensionally by the placement of substituents around one or more atoms in a molecule.Ĭhiral carbon (asymmetric carbon):A carbon that is attached to four different types of atoms or groups of atoms.Īnomeric carbon: A carbon derived from the carbonyl carbon (the ketone or aldehyde functional group) of the open-chain form of the carbohydrate molecule. The α form of glucose has the anomeric OH group opposite from the CH₂OH group, while the β form has the anomeric OH group on the same side as the CH₂OH group.Įpimers: A type of stereoisomer that differs in configuration at a single stereogenic center (the anomeric carbon).Īnomers: A type of stereoisomer that differs in configuration at the hemiacetal or acetal carbon they are a specific type of epimer.Anomers differ in position at the anomeric carbon they are a special type of epimer.Epimers differ in the position of the atoms attached at one chiral carbon.The β form has the anomeric OH group on the same side as the CH₂ OH. The α form has the anomeric OH group at C-1 on the opposite side of the ring from the CH₂ OH group at C-5. For example, α-D-glucose and β-D-glucose below are anomers. The carbon atom that forms the new chiral center (C-1) is called the anomeric carbon.Īnomers are special cases of epimers that differ in position at the anomeric carbon in particular. When a molecule such as glucose converts to a cyclic form, it generates a new chiral center at C-1. Glucose and mannose are epimers that differ at the C-2 carbon, while glucose and galactose are epimers that differ at the C-4 carbon, as shown below. In the examples below, the difference in the position of the hydroxyl (OH) at one chiral carbon creates a pair of epimers. Epimers and anomers are types of stereoisomers of carbohydrates that differ in the position at a single carbon atom.Įpimers are stereoisomers that differ in the configuration of atoms attached to a chiral carbon.
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