:Haworth projection

{{Short description|Method for writing structural formulas of monosaccharide molecules}}

Image:Haworth projection of α-D- and α-L-Glucopyranose.svg and α-L-glucopyranose]]

In chemistry, a Haworth projection is a common way of writing a structural formula to represent the cyclic structure of monosaccharides with a simple three-dimensional perspective. A Haworth projection approximates the shapes of the actual molecules better for furanoses—which are in reality nearly planar—than for pyranoses that exist in solution in the chair conformation.{{Cite book |last=Campbell |first=Mary K. |url=https://www.worldcat.org/oclc/651905707 |title=Biochemistry |date=2012 |publisher=Brooks/Cole, Cengage Learning |others=Shawn O. Farrell |isbn=978-0-8400-6858-3 |edition=7th |location=Belmont, CA |page=456 |chapter=16 |oclc=651905707}} Organic chemistry and especially biochemistry are the areas of chemistry that use the Haworth projection the most.

The Haworth projection was named after the British chemist Sir Norman Haworth.{{cite book |last1=Haworth |first1=Walter Norman |title=The Constitution of Sugars |date=1929 |publisher=Edward Arnold & Co. |location=London, England}}

A Haworth projection has the following characteristics:{{GoldBookRef|title=Haworth representation|file=H02749}}

• Carbon is the implicit type of atom. In the example on the right, the atoms numbered from 1 to 6 are all carbon atoms. Carbon 1 is known as the anomeric carbon.
• Hydrogen atoms on carbon are implicit. In the example, atoms 1 to 6 have extra hydrogen atoms not depicted.
• A thicker line indicates atoms that are closer to the observer. In the example on the right, atoms 2 and 3 (and their corresponding OH groups) are the closest to the observer. Atoms 1 and 4 are further from the observer. Atom 5 and the other atoms are the furthest.
• The groups below the plane of the ring in Haworth projections correspond to those on the right-hand side of a Fischer projection. This rule does not apply to the groups on the two ring carbons bonded to the endocyclic oxygen atom combined with hydrogen.