Principles of Biochemistry

3.2.1.1.1 Stereochemistry

Stereochemistry is the study of the arrangement of atoms in three-dimensional space. Stereoisomer is compounds in which the atoms are linked in the same order but differ in their spatial arrangement. Many carbohydrates exhibit stereoisomerism as they contain the same number of atoms and the same kinds of group but have different chemical and biological properties. This is due to the presence of asymmetric carbon atom in the structure.

A carbon atom attached to four different atoms or groups is called an asymmetric carbon atom. When there are many asymmetric carbon atom in a chain molecule the number of stereoisomer possible is equal to 2ⁿ, where n is the number of asymmetric carbon atoms. The simple sugars corresponding to the formula C₆H₁₂O₆ have 4 asymmetric carbon atoms and hence have 2⁴ = 16 stereoisomer each have identical functional groups but with different spatial configurations. This is due to the presence of asymmetric carbon atom in the structure.

Glucose has 4 asymmetric carbon atoms (2, 3, 4 & 5). The structure of glucose can be represented in three ways (1) the straight - chain structural formula (aldohexose, as simple ring or a chair form.