Cyclic Haworth structures

Convert the following Fischer structures into cyclic Haworth structures QUESTION 7.3... 

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 ... 

He favored the currently accepted, cyclic hemiacetal structure for the glucosides, but formulated them with the furanoid ring for glucose proposed in 1883 by B. Tollens. W. N. Haworth later established that the glucose residue in such glucosides is present in the form of a pyranoid ring. 

Fructose forms a five-membered cyclic hemiacetal. Five-membered rings are usually represented as flat Haworth structures. 

Haworth perspective formulas. A method for representing cyclic chemical structures (sugars) in order to define the configuration around each chiral center. 

In 1926 W. N. Haworth demonstrated that sugars were cyclic in structure and that the points of attachment of the oxygen atom in the ring were the first and the fifth carbon atoms as shown in (2). 

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)... 

The aldohexose D-galactose exists predominantly in cyclic forms. Given the structure below, draw the Haworth structure for the anomer. Label the new compound as a or p. 

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. 

As you study the open chain and cyclic hemiacetal forms of D-glucose, note that, in converting from a Fischer projection to a Haworth structure,... 

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

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... 

Activity in the field was, however, expanding. For example, in 1927 Drew and Haworth (65) obtaind a crystalline polymeric powder by the action of hydrogen chloride on the lactone of 2,3,4-trimethyl-l-arabonic acid. Citing the increase in melting point and molecular weight, and loss of specific optical rotation, they ascribed a cyclic, high polymer structure to this polyester. 

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... 

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. 

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. 

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