Principles of Biochemistry (2+1)

When  a monosaccharide cyclizes, the carbonyl carbon, called the anomeric carbon, becomes a chiral center with two possible configurations. The pair of stereoisomers that differ in configuration at the anomeric carbon are called anomers. In the α anomer, the -OH substitutent of the anomeric carbon is on the opposite side of the sugar ring from the -CH₂OH group at the chiral center that designates the D or L configuration(C5 in hexoses). The other  form is known as the ß anomer.

The two anomers of D-glucose have slightly different physical and chemical properties, including different optical rotations. The anomers freely interconvert in aquous solution, so at equilibrium, D-glucose is a mixture of the ß anomer (63.6%) and the α anomer (36.4%). The linear form is normally present in only minute amounts.