Haworth projection formulas

The rules previously mentioned for assignment of a- and /3-configurations can be readily applied to Haworth projection formulas. For the D-sugars, the anomeric hydroxyl group is below the ring in the a-anomer and above the ring in the /3-anomer. For L-sugars, the opposite relationship holds. 

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... 

Figure 9.8 Haworth projection formulae. The ring is considered to be planar with the substituent groups projecting above or below the plane. The thickened lines represent the portion of the ring that is directed out of the paper towards the reader. The alpha and beta anomeric forms are shown with the hydroxyl group at carbon 1 below or above the plane of the ring respectively.

The planar Haworth projection formulae bear little resemblance to the shape of the six-membered pyranoses that actually adopt a non-planar ring conformation comparable to that of cyclohexane. The chair form is the most... 

Give an adequately descriptive name of the disaccharide, and draw its Haworth projection formula. 

Figure 20-4 Haworth projection formulas showing the formation and reactions of O-methyl derivatives of glucose. The notation (H.OH) in 20 means that the anomeric configuration is unspecified.

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... 

Two sugars can link to each other by losing water from OHs to form disaccharides. Figure 4.6 shows the Haworth projection formulas of four important disaccharides sucrose, lactose, maltose, and cellobiose, which all have the same molecular formulas, C12H22011. Sucrose and lactose are the most abundant and most important disaccharides of natural origin. Maltose and cellobiose are repeating units of polymeric starch and cellulose, respectively. Disaccharides may hydrolyze to form two monosaccharide molecules. 

The Haworth projection formulas are neater ways of writing the ring forms shown in the equilibria above and yet preserving the configuration shown at each chiral carbon. It is not difficult to translate the open-chain structure for a monosaccharide into the Haworth ring structure. 

Question How do we translate the open-chain form of glucose into five-membered Haworth projection formulas and assign the symbols a and p to the appropriate formula ... 

Haworth projection formulas of anomers of D-glucopyranose. The thick line of the structure projects out toward the observer, and the upper edge (thin line) projects behind the plane of the paper. 

Fig. 3 Haworth projection formula for cellulose, Reproduced with permission from American Institute of Physics...

Fig. 1. Chemical structures for simple sialic acids in different views, (a) S-amino-S.S-dideoxy-D-gfycero-D-ga/acro-non-2-ulosonic acid (Neu, open chain, Fischer projection formula) (b) 5-acetaraido-3,5-dideoxy-D-g/> cero-a-D-gfl/acto-non-2-ulopyranosonic acid (a-Neu5Ac, Fischer projection formula, note that C7 is the anomeric reference atom) (c) a-Neu5Ac (Haworth projection formula) (d) a-Neu5Ac ( 5 chair conformation) (e) 3-deoxy-D-g/ycero-3-D-gfl/acto-non-2-ulopyranosonic acid (P-Kdn, 5 chair conformation). Note that the D-notation is part of the trivial name.

CONFORMATIONAL STRUCTURES Although Haworth projection formulas are often used to represent carbohydrate structure, they are oversimplifications. Bond angle analysis and X-ray analysis demonstrate that conformational formulas are more accurate representations of monosaccharide structure (Figure 7.10). Conformational structures are more accurate because they illustrate the puckered nature of sugar rings. 

Sugars exist predominantly as cyclic molecules rather than in an open-chain form. Haworth projection formulas are more realistic representations of the cyclic forms of sugars than are Fischer projection formulas. Many stereoisomers are possible for five- and six-carbon sugars, but only a few of the possibilities are encountered frequently in nature. 

Reflect and Apply Draw Haworth projection formulas for dimers of glucose with the following types of glycosidic linkages ... 

Scheme 7 Relationship of the Fischer and Haworth projection formulas illustrated for P-L-arabinofuranose.

The Haworth projection formula presents a nominally planar ring with... 

Draw Haworth projection formulas of the disaccharides maltose and sucrose. Label the hemiacetal, hemiketal, acetal, or ketal carbons. 

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

Using Figure 16.1 if necessary, write a Fischer projection formula and a Haworth projection formula for... 

Draw the Haworth projection formula of the hemihetal of 5-hydroxy-2-hexanone. 

Draw the Haworth projection formulas of the two glycosides derived from each of the following pairs of components. 

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