Fructose, formula

Investigations by Haworth and many others have made it probable that a D-fructopyranose structure is to be assigned to crystalline D-fructose. Formulas III and IV below illustrate the interconversion of... 

Carbohydrates may be divided into monosaccharides, disaccharides and polysaccharides. The monosaccharides under certain conditions react as polyhydroxy-aldehydes or polyhydroxy-ketones two important representatives are glucose CjHjjO (an aldose) and fructose (laevulose) CgHuO, (a ketose). Upon hydrolysis di- and polysaccharides 3deld ultimately monosaccharides. Common disaccharides are sucrose, lactose and maltose (all of molecular formula C,2H2. 0,), whilst starch, dextrin and cellulose, (CjHjoOj), in which n > 4, are typical polysaccharides. 

Therapeutic Function Fluid and nutrient replenisher Chemical Name Fructose Common Name Levulose and fruit sugar Structural Formula h... 

In dilute acidic solution, sucrose (Ci2H22Ou) decomposes to glucose and fructose, both with molecular formula C6Hi2Ofi. The following data are obtained for the decomposition of sucrose. 

Write a chemical equation, using molecular formulas, for the reaction of sucrose with water to form glucose and fructose. 

Draw a structural formula for the fructose molecule (remember that fructose is an isomer of glucose). Explain why fructose cannot be oxidized to a six-carbon acid. 

Aldose-ketose isomerism Fructose has the same molecular formula as glucose but differs in its structural formula, since there is a potential keto group in position 2, the anomeric carbon of fmctose (Figures 13 and 13-7), whereas there is a potential aldehyde group in position 1, the anomeric carbon of glucose (Figures 13-2 and 13-6). 

Cellulose and starch are macromolecules with empirical formulas that resemble hydrated carbon, CX (H2 0)y, where x and y are integers. The monomers from which these macromolecules are consfructed are sugars such as glucose and fructose. These monomers and macromolecules are the carbohydrates. Structurally, carbohydrates are very different from simple combinations of carbon and water. Even the smallest carbohydrates contain carbon chains with hydrogen atoms, OH groups, and occasional ether linkages. 

Although the chemical formulas indicate that ribose is a pentose and fructose is a hexose, the ring portions of the structures are the same size. Proceeding clockwise around the rings from the oxygen atom, we see that the structures differ at the first two positions. In the first position, ribose has a carbon atom bonded to —H and —OH, while)S-fructose has a carbon bonded to —OH and — CH2 OH. In the second position the molecules have the same two bonds but in different orientations. The OH group points up in y6-fructose and down in ribose. The two molecules have the same structures at the other positions. 

The establishment of the structure of turanose furnishes a firm basis for an eventual determination of the structure of melezitose. One can start with the assurance that the trisaccharide is 8-[a-v-glucopyranosyVy D-fructose < > n-glucopyranose this formula requires three further specifications. The first of these is an allocation of a ring to the fructose unit, the second is a decision between the a- and /S-forms for this unit, and the third is a similar decision between these forms for the right-hand D-glucopyranose unit. Decision on these three matters can be made readily if sucrose should ever be found to result from a partial hydrolysis of melezitose, because sucrose is almost certainly f)-v-fructo-... 

Early reports on levan are obscured by incomplete descriptions of impure products.2 96 Greig-Smith found that Bacillus levaniformans(1) produced levan from sucrose96" in suitable nutrient solutions, but not from D-glucose, D-fructose, lactose or maltose.966 He therefore assumed that levan could only be formed from the nascent D-fructose and D-glucose resulting from the inversion of sucrose. Hydrolysis of levan yielded D-fructose only, and analysis of levan agreed with the empirical formula (C HiriOi) it was noted that levan was closely related to inulin but was not identical with it. 

If di-D-fructose anhydride II has formula XIX, a mixture of 1,3,4-and 1,4,6-trimethyl-D-fructoses would be present in the hydrolytic product. Such a mixture would have a specific rotation of — 10° to — 20° (water) in contrast to the value of + 25 to + 30 found by McDonald and Jackson.76 The rotation of 1,4,6-trimethyl-D-fructose was measured by Montgomery76 in chloroform (+ 29.7°), but it has not been measured directly in water. However, the hydrolysis data of McDonald and Jackson76 for hexamethyl-di-D-fructose anhydride III show that 1,4,6-trimethyl-D-fructose has about the same rotation in water as in chloroform. The argument thus appears to exclude structure XIX. 

An anhydride whose formula is represented by XVII would yield a mixture of 3,4,6-trimethyl-D-fructose and 1,3,6-trimethyI-D-fructose when its hexamethyl derivative was hydrolyzed. Available data concerning di-D-fructose anhydride II are at least in accord with this structure, and if the present inferences are accepted, one may conclude that the rotation of 1,3,6-trimethyl-D-fructose is near those of 1,4,6- and 3,4,6-tri-methyl-D-fructose. 

Hereditary fructose intolerance is due to aldolase B deficiency and is often diagnosed when babies are switched from formula or mother s milk to a diet containing fructose-based sweetening, such as sucrose or honey. 

FIGURE 7-7 Pyranoses and furanoses. The pyranose forms of o-glucose and the furanose forms of o-fructose are shown here as Haworth perspective formulas. The edges of the ring nearest the reader are represented by bold lines. Hydroxyl groups below the plane of the ring in these Haworth perspectives would appear at the right side of a Fischer projection (compare with Fig. 7-6). Pyran and furan are shown for comparison. 

Compounds that have the same chemical formula but have different structures are called isomers. For example, fructose, glucose, mannose, and galactose are all isomers of each other, having the same chemical formula, C6H1206. If two monosaccharides differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon, see anomers below), they are defined as epimers of each other. (Of course, they are also isomers ) For example, glucose... 

Another sugar called glucose (CeH, Os) is found in ripe fruits, often in the company of still another sugar of the same formula called fructose (C6H, 06). These two sugars can be made in the laboratory by treating the more complicated sucrose with an acid. The sucrose picks up water and splits into glucose and fructose by a process known as inversion ... 

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