Final answer:
True, alpha-D-fructose and beta-D-fructose are anomers, differing at the anomeric carbon in their cyclic form with the hydroxyl group oriented either 'down' (alpha) or 'up' (beta) in relation to the methyl group.
Step-by-step explanation:
True, alpha-D-fructose and beta-D-fructose are anomers. Anomers are stereoisomers of cyclic saccharides that differ only at the anomeric carbon, which is the carbon atom that was originally the carbonyl carbon atom (C=O) in the open-chain form. In the case of D-fructose, which is a ketose, this anomeric carbon is the second carbon atom in the ring structure, rather than the first as it is in aldoses like glucose and galactose.
For alpha-D-fructose, the hydroxyl group (-OH) on the anomeric carbon is positioned on the opposite side of the ring from the methyl group (-CH3), technically 'down' in Haworth projection. In contrast, for beta-D-fructose, the hydroxyl group on the anomeric carbon is on the same side as the methyl group, or 'up'. These two different configurations are due to the two possible positions of the hydroxyl group when the cyclic form of fructose forms from its straight-chain counterpart.
Additionally, D-fructose can form five-membered and six-membered rings, known as furanose and pyranose forms, respectively, but the existence of anomers is independent of whether it is a furanose or a pyranose ring.