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Structural formulas of the open-chain and cyclic forms of the pentose ribose

Several of the forms of D-ribose: the open-chain form (top), and Haworth projections of two of the four cyclic forms, alpha-D-ribopyranose (middle), and beta-D-ribofuranose (bottom). Ribose exists as a mixture of cyclic forms in equilibrium with its linear form, and these readily interconvert, especially in aqueous solution. The relative abundance of forms of ribose in solution is as follows: beta-D-ribopyranose (59%), alpha-D-ribopyranose (20%), beta-D-ribofuranose (13%), alpha-D-ribofuranose (7%), and open-chain (0.1%). The name "ribose" refers collectively to all of these forms, although the more specific names for each form are used when required. D-ribose was discovered in 1909 by Lithuanian-American biochemist Phoebus Levene. (Public domain.)