Monosaccharides cyclic Haworth structures

In drawing cyclic Haworth structures of monosaccharides, certain rules should be followed so that all our structures will be consistent. First we must draw the ring with its oxygen to the back ... 

Monosaccharides are sweet-tasting solids that are very soluble in water. Noncarbohydrate low-calorie sweeteners such as aspartame have been developed as sugar substitutes. Pentoses and hexoses form cyclic hemiacetals or hemiketals whose structures can be represented by Haworth structures. Two isomers referred to as anomers (the a and p forms) are produced in the cyclization reaction. All monosaccharides are oxidized by Benedict s reagent and are called reducing sugars. Monosaccharides can react with alcohols to produce acetals or ketals that are called glycosides. 

Monosaccharides commonly form internal hemiacetals or hemiketals, in which the aldehyde or ketone group joins with a hydroxyl group of the same molecule, creating a cyclic structure this can be represented as a Haworth perspective formula. The carbon atom originally found in the aldehyde or ketone group (the anomeric carbon) can assume either of two configurations, a and /3, which are interconvertible by mutarotation. In the linear form, which is in equilibrium with the cyclized forms, the anomeric carbon is easily oxidized. 

Haworth projection common way of representing the cyclic structure of monosaccharides using a three-dimensional perspective. 

A major drawback of cyclic Fischer projections is the unrealistic manner in which the structures are depicted. In 1929, Haworth designed a representation to address this deficiency. Haworth projections provide a simple way to represent cyclic monosaccharides with a three-dimensional perspective. The following process allows the conversion of a Fischer projection into a Haworth representation ... 

Using methods similar to Fischer s, the straight-chain form of any monosaccharide can be worked out. As we have seen, however, monosaccharides exist mostly as cyclic pyra-nose or furanose hemiacetals. These hemiacetals are in equilibrium with the open-chain forms, so sugars can react like hemiacetals or like ketones and aldehydes. How can we freeze this equilibrium and determine the optimum ring size for any given sugar Sir Walter Haworth (inventor of the Haworth projection) used some simple chemistry to determine the pyranose structure of glucose in 1926. 

Given the linear structure of a monosaccharide, draw the Haworth projection of its a- and p-cyclic forms and vice versa. 

The depictions of glucopyranose and fructofuranose shown in Figures 11.4 and 11.5 are Haworth projections. In such projections, the carbon atoms in the ring are not explicitly shown. The approximate plane of the ring is perpendicular to the plane of the paper, with the heavy line on the ring projecting toward the reader. Like Fischer projections, Haworth projections allow easy depiction of the stereochemistry of sugars. We will return to a more structurally realistic view of the conformations of cyclic monosaccharides shortly. 

Haworth formulas are named after the English chemist W. N. Haworth (University of Birmingham), who, in 1926, along with E. L. Hirst, demonstrated that the cyclic form of glucose acetals consists of a six-membered ring. Haworth received the Nobel Prize for his work in carbohydrate chemistry in 1937. For an excellent discussion of Haworth formulas and their relation to open-chain forms, see The Conversion of Open Chain Structures of Monosaccharides into the Corresponding Haworth Formulas, Wheeler, D. M. S., Wheeler, M. M., and Wheeler, T. S.,J. Chem. Educ. 1982, 59, 969-970. 

Cyclic monosaccharide structures are often drawn as Haworth projections in... 

The term Haworth Structnres is now used for the term cyclic structures for monosaccharides, disaccharides, and... 

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