Haworth perspective formulas of cyclic sugars
Definition: perspective representations of furanose or pyranose structures as pentagons or hexagons, respectively, with the connecting bonds so shaded as to make them appear as though the plane of the ring is at a 30° angle to the plane of the paper, and the bonds to H and OH at right angles to the plane of the ring. These formulas depict the planar conformation, a situation not usually met. Other conformational formulas, the Haworth conformational formulas of cyclic sugars, attempt to depict the many deviations from planarity. The basic conventions in Haworth formulas of cyclic sugars (cyclic glycoses) are 1) The lowest-numbered asymmetric ring-carbon atom is depicted at the right. 2) If the highest-numbered asymmetric carbon atom is d, the sugar is d; the formula of an l-glycose may be derived from that of its d-isomer by reversing the up or down direction of all groups attached to the ring-carbon atoms or simply by drawing the mirror image of the entire structure.. 3) If the hydroxyl group attached to the anomeric carbon (C-1 in aldoses, C-2 in 2-ketoses) is below the plane of the ring of a d-glycose, it is α; if above, it is β; the reverse applies if the sugar is l.
[Sir Walter Norman Haworth]
See Also: Fischer projection formulas of sugars
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