Question

what is meant by anomeric carbon?
select the correct answer below:
it is the carbon where the hydroxyl group is always in the same up or down position on the haworth structure regardless of how the ring closes.
it is a carbon that is not part of the ring when a monosaccharide is in ring form.
it is the carbon where the hydroxyl group can be arranged up or down in the haworth structure depending on how the ring closes.
none of the above

Explanation:

An anomeric carbon is a carbon derived from the carbonyl carbon (the ketone or aldehyde functional group) of the open - chain form of the carbohydrate (aldose or ketose). In the cyclic (ring) form of a monosaccharide (Haworth structure), the anomeric carbon has a hydroxyl group that can be in either an "up" or "down" position (α or β configuration) depending on how the ring closes. For example, in glucose, when it forms a cyclic structure, the carbonyl carbon (C - 1 in glucose) becomes the anomeric carbon, and its hydroxyl group orientation (up or down) gives α - D - glucose or β - D - glucose.

• Option A is incorrect because the hydroxyl group on the anomeric carbon is not always in the same position.
• Option B is incorrect as the anomeric carbon is part of the ring structure in cyclic monosaccharides.

Answer:

C. It is the carbon where the hydroxyl group can be arranged up or down in the Haworth structure depending on how the ring closes.