Haworth projections cyclic structures

The cyclic forms adopted by the hexoses and pentoses can be depicted as symmetrical ring structures called Haworth projection formulae, which give a better representation of the spatial arrangement of the functional groups with respect to one another. The nomenclature is based on the simplest organic compounds exhibiting a similar five- or six-membered ring... 

A more realistic representation for the hemiacetal ring structure is the Haworth projection formulas. The formulas for a-D-glucose are shown in Figure 4.3. The shorthand form of the Haworth projection eliminates the Hs and indicates OHs by dashes. Five- and six-membered cyclic sugars are called furanose and pyranose, respectively.3... 

Draw the cyclic structures (Haworth projection and conformational structure) for a-D-and p-D-glucose and the corresponding methyl glycosides. 

The cyclic structures are called Haworth projections. In a Haworth projection, the lower horizontal bond in the ring is understood to be projected towards you, above the plane of the page. This bond is usually in boldface. The upper horizontal bond is understood to be projected away from you, behind the plane of the page. 

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 ... 

The cyclic structure is often drawn initially in the Haworth projection, which depicts the ring as being flat (of course, it is not). The Haworth projection is widely used in biology texts, but most chemists prefer to use the more realistic chair conformation. Figure 23-6 shows the cyclic form of glucose both as a Haworth projection and as a chair conformation. 

Draw the Haworth projection for the cyclic structure of D-mannose by laying down the Fischer projection. 

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. 

Eischer projections are not the best way to show the structure of a cyclic sugar, because of how the C—O—C bond is represented. A somewhat more satisfactory representation is given by a Haworth projection. 

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. 

The cyclic structures of carbohydrates are referred to as Haworth structures or Haworth projections. 

Fischer s open-chain structure for (+)-glucose with its Fischer projection and two (incorrect) cyclic structures for its metiiyl glucosides (top). Haworth s correct assi iment of a six-memhered ring for glucose and Haworth structures for the two anomers of (+)-glucose (bottom)... 

PROBLEM 16.5 Draw the Haworth projection formula for the six-membered cyclic structure of D-galactose. 

A five-membered ring is so close to being planar that Haworth projections are adequate representations of furanoses. For pyranoses, however, the six-membered ring is more accurately represented as a chair conformation. Following are structural formulas for a-D-glucopyranose and 8-D-glucopyranose drawn as chair conformations. Also shown is the open-chain or free aldehyde form with which the cyclic hemiacetal forms are in equilibrium in aqueous solution. 

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

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