anomer

In carbohydrate chemistry, anomers () are specific types of stereoisomers found in sugars.

Many common sugars, such as glucose, exist in both a linear (or open-chain) form and a cyclic (or ring) form. The ring is formed when one end of the sugar molecule connects to the other end. The carbon atom where this ring closure occurs is called the anomeric carbon. Depending on the direction from which the connection is made, this anomeric carbon can have its new group (–OH) pointing in one of two distinct orientations, typically visualized as "up" or "down" in a standard diagram. These two resulting molecules are the anomers and are labeled with the Greek letters alpha (α) or beta (β).