Haworth drawings

Figure 2.27) ° In these drawings the cyclic hemiacetal form of the carbohydrate is shown as a six-membered ring in the chair conformation. An older representation of carbohydrates that represents structures with planar six-membered rings is the Haworth drawing 64b. ... 

Certain chemical families, notably carbohydrates, possess such a high density of stereocenters that they cannot be aesthetically depicted with wedges and hashes. The only recourse is to deal in Haworth drawings or Fischer projections. This work belongs to an exciting frontier in chemical perception. ... 

Structural drawings of carbohydrates of this type are called Haworth formulas, after the British chemist Sir Walter Norman Haworth (St Andrew s University and the University of Birmingham) Early m his career Haworth contributed to the discovery that carbohydrates exist as cyclic hemiacetals rather than m open chain forms Later he col laborated on an efficient synthesis of vitamin C from carbohydrate precursors This was the first chemical synthesis of a vitamin and provided an inexpensive route to its prepa ration on a commercial scale Haworth was a corecipient of the Nobel Prize for chem istry m 1937... 

Draw Haworth structures for the two possible isomers of D-altrose (Figure 7.2) and D-psicose (Figure 7.3). 

It is sometimes desirable to draw Haworth formulae with the ring in other orientations (see Chart II), when there are bulky substituents to be represented, or when linkages in oligo- or poly-saccharides are to be shown. If the ring is inverted [as in (g)-(l)], the numbering runs counterclockwise. 

Fig. 3.—Formulas Representing KDO (1). [a, Fischer projection-formula (acyclic form) b, Haworth formula (ketopyranose) c, conformational drawing (ketopyranose).]...

Haworth structures are easy to draw and unambiguous in depicting configurations,14 but they also do not show the spatial relationships of groups attached to other rings correctly. For this reason conformational formulas of the type described in Section 2 and shown in Fig. 4-4 are used most often in this book. 

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

Exercise 20-10 Draw Haworth and conformational structures for each of the following disaccharides ... 

Exercise 20-15 Write Fischer projections, Haworth projections, and sawhorse conformational drawings for the following ... 

Haworth structures are unambiguous in depicting configurations, but even they do not show the true spatial relationship of groups attached to rings. The normal angle between the bonds formed by the saturated carbon atoms (109°) causes the pyranose molecule to pucker into either a chairlike or boatlike conformation. For glucose and most other pyranoses the chair form (fig. 12.6c) predominates. However, we usually display pyranoses by the Haworth projection because it is easier to draw. 

Comparison of the Fischer (a) and Haworth (b) projections for a- and /3-D-glucose. The Haworth projection is a step closer to reality. Chair configurations for the two anomers of D-glucose are the most accurate depiction (c) but they are not always used because of the difficulty in drawing. Note that the largest substituent, —CH2OH, is in an equatorial location in both structures. The differences between the two anomers are shown in color. 

Figure 4.4. However, despite the inaccuracy of the Haworth formulas, they are used more frequently than the chair conformation, because they are easier to draw and interpret.

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

Draw as Haworth projections the products from the addition of bromine to ( )-4-chlorocyclohex-l-ene. 

Close the ring, and draw the result. Always draw the Haworth projection or chair conformation with the oxygen at the back, right-hand comer, with Cl at the far right. Cl is easily identified because it is the hemiacetal carbon—the only carbon bonded to two oxygens. The hydroxyl group on Cl can be either up or down, as discussed in Section 23-7. 

Draw the cyclic hemiacetal forms of D-mannose and D-galactose both as chair conformations and as Haworth projections. Mannose is the C2 epimer of glucose, and galactose is the C4 epimer of glucose. 

The simplest way to draw Haworth structures for these two sugars is to draw the chair conformations and then draw the flat rings with the same substituents in the up and down positions. For practice, however, let s lay down the Fischer projection for galactose. You should follow along with your molecular models. 

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

Allose is the C3 epimer of glucose. Draw the cyclic hemiacetal form of D-allose, first in the chair conformation and then in the Haworth projection. 

Draw the following monosaccharides, using chair conformations for the pyranoses and Haworth projections for the furanoses. 

Draw a Haworth Projection from an Acyclic Aldohexose... 

Convert each aldohexose to the indicated anomer using a Haworth projection, a. Draw the a anomer of b. Draw the a anomer of c. Draw the p anomer of ... 

Draw a Haworth projection for each compound using the structures in Figures 27.4 and 27.5. 

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

Drawing the Haworth Projection of a Monosaccharide from the Structural Formula... 

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