Final answer:
A cyclic monosaccharide is in the beta form when the hydroxyl group on the anomeric carbon, C1, is located above the ring plane. This beta configuration is distinct from the alpha form, where the hydroxyl group is below the ring plane. These two forms are known as anomers and are differentiated by their distinct physical and chemical properties.
Step-by-step explanation:
On the anomeric carbon, C1, of a cyclic monosaccharide, the hydroxyl group (OH) must be located above the plane of the sugar ring to classify the molecule as a beta anomer. In contrast, when the OH group is positioned below the plane of the sugar ring, the molecule is referred to as an alpha anomer. This distinct configuration at the anomeric carbon results in two different stereoisomers, known as anomers.
Specifically, in beta anomer forms, the OH group on the anomeric carbon is oriented in the same direction as the methoxy (CH2OH) group, usually the axial position if drawn in the Haworth projection. This is important because these configurations have different physical and chemical properties, and biological systems can distinguish between them.
The process of forming cyclic structures is known as cyclic hemiacetal formation, and these structures can freely interconvert in solution with the open-chain form, a phenomenon known as mutarotation. The exact position of the OH groups on the anomeric carbon is crucial for the proper identification and function of the sugars in biological systems.