Multiple Choice
D-ribose is an aldopentose sugar that is found in the DNA. It commonly exists as a five-membered β anomer. Draw D‑ribose in its cyclic hemiacetal form.
20. Carbohydrates
Cyclic Structures of Monosaccharides
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Draw a Haworth projection for α-D-altrose.
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Verified step by step guidance1
Identify the structure of D-altrose from the Fischer projection. D-altrose is an aldohexose, which means it has six carbon atoms and an aldehyde group.
Convert the Fischer projection to a Haworth projection. To do this, first determine the ring size. For D-altrose, the ring will be a six-membered pyranose ring.
Number the carbon atoms in the Fischer projection starting from the aldehyde group as carbon 1. The hydroxyl group on carbon 5 will attack the aldehyde group to form the cyclic structure.
In the Haworth projection, place the oxygen atom at the top right of the ring. The CH2OH group on carbon 5 will be placed above the plane of the ring for D-sugars.
For the α-anomer, the hydroxyl group on carbon 1 (anomeric carbon) will be placed below the plane of the ring. Arrange the other hydroxyl groups according to their positions in the Fischer projection: if they are on the right in the Fischer projection, they will be below the plane in the Haworth projection, and vice versa.
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