What is anomer


1 definition

Anomers are special stereoisomers of carbohydrates (monosaccharides in the cyclic hemiacetal form), which differ in the configuration at the former carbonyl carbon atom.

2 chemistry

If a ring closure to the cyclic hemiacetal is formed, a new center of chirality is created, since the carbon atom of the aldehyde group becomes tetravalent (tetrahedral) and bears four different substituents. If the compound is represented in the Haworth formula, the new OH group can lie above the plane of the ring and point in the same direction as the CH2OH group at C-5. In this case one speaks of the β-form. If, on the other hand, the OH group points downwards, the molecule is in the α form. This forms from the open-chain D.-Glucose the β-D.-Glucopyranose and α-D.-Glucopyranose. In aqueous solutions, both are in equilibrium with one another via the open-chain form (<1%) (ratio α: β = 36:64).

Stereoisomeric carbohydrates that are in cyclic hemiacetal form and differ in configuration at the former carbonyl C atom (CO) are called anomers (α or β anomer).

3 mutarotation

If the α-anomer ([α]D. = + 112 °) dissolved in water, the rotation value slowly decreases and after a certain time reaches a constant value ([α]D. = + 53 °). The rotation value increases up to this certain amount, provided that pure β-anomers are assumed ([α]D. = + 19 °). This process is known as mutarotation. This rotation occurs because equilibrium is established between the anomers. In addition, the anomers are the D.-Glucopyranose diastereomers and possess different physical properties.

4 literature

  • "Chemistry for Medicine" - A. Zeeck et. al., Urban & Fischer-Verag, 7th edition