Haworth projection

Meaning: A Haworth projection is a flat drawing of a cyclic sugar. The ring is viewed edge-on, with the ring oxygen at the back right and the anomeric carbon at the right. The ring forms when a hydroxyl attacks the carbonyl carbon, giving a hemiacetal (aldose) or a hemiketal (ketose). Six-membered rings are pyranoses and five-membered rings are furanoses. Each substituent points up or down from the ring.

On the MCAT: To convert a D-sugar from a Fischer projection, groups on the right point down and groups on the left point up. The terminal CH₂OH points up in D-sugars. The anomeric OH sets α or β: α is trans to the CH₂OH (down in D-sugars) and β is cis (up). Expect questions that ask you to identify anomers, epimers or ring size. Expect others on α and β forms interconverting through the open-chain form (mutarotation).

Common confusion: Students memorize "α = down" and apply it to every sugar. It holds for D-sugars because α is defined relative to the CH₂OH group, so it flips for L-sugars. The flat ring is also a simplification. Real pyranose rings are puckered chairs, not planar hexagons.