Pyranose sugars, anomeric carbon atom

The anomeric carbon atom, C-l, in pyranose and furanose sugars is unique in that it is the only carbon atom in these molecules which is bonded to two atoms which are more electronegative. These more-electronegative atoms necessarily have lone-pair electrons. It is the electronic structure which arises from the electronegativity differences and the presence of these lone-pair electrons that gives rise to the special reactivity and structural properties of the anomeric carbon center. 

The introduction of an additional asymmetric carbon atom leads to the existence of two isomers, (a and j8) of each type of ring, which are described as anomers, and C-i is now referred to as the anomeric carbon atom (C-2 in ketoses). In the D-series of sugars the a-hydroxyl is written on the right of the sugar chain in the cyclic form of the Fischer formulae and trans to the CHjOH in the Haworth formulae. It is necessary to relate the pento-pyranoses to the hexoses to determine whether the anomeric hydroxyl... 

Anomeric center (Section 21.5) The hemiacetal carbon atom in the cyclic pyranose or furanose form of a sugar. 

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