Stereoisomers are compounds with the same structural formula but different spatial configuration. A carbon atom is said to be asymmetric if it is attached to four different chemical groups. Monosaccharides contain at least one asymmetric carbon. Isomers are formed due to the presence of asymmetric carbon. The number of isomers in a compound depends on the number of asymmetric carbon atoms (n) and is equal to 2ⁿ. For example, glucose has four asymmetric carbon atoms and thus has 2⁴ = 16 isomers.