Structures of Glucose and Fructose

For references see Beilsteins Handbuch der organischen Chemie, Vol. 31, p. 83. Springer, Berlin, 1938. 

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There is another aspect of the structure of glucose and fructose. They, like other simple sugars, can exist as a straight chain but this form is in equilibrium with a cyclic structure. In solutions the latter form prevails. Reaction (2) shows both forms of glucose. 

Note that the system is complex because glucose and fructose exist as equilibria of 6-and 5- ring hcmi-acetal structures (mutarotation). Each structure has its adsorption strength to and hydrogenation rate at the metal catalyst. By contrast the enzyme accepts and produces only on mutarotation structure of glucose and fructose. 

Figure 13.17.1 The molecular structure of sucrose, a disaccharide of glucose and fructose. Asterisks indicate the hydroxyl groups replaced with chlorine atoms in the synthetic sweetner.

Sucrose is composed of glucose and fructose, and again we have a six-membered pyranose ring coupled to a five-membered furanose ring. However, there is a significant difference when we compare its structure with that of lactulose in sucrose, the two sugars are both linked through their anomeric... 

Fig. 2.9 Synthesis of sucrose. See text (Modified from Fig. 20-13 in Berg JM, Tymoczko JL and Stiver L. Biochemistry, 5th Ed. 2002. W.H. Freeman Co., New York to also show the phosphatase step). Note The diagram of fructose in this figure (red) is rotated so that its anomeric carbon atom (C2) lies to the right of the ring structure instead of the left as in a conventional diagram. Because of the rotation, it is not obvious that the fructose bond in sucrose is in the (3-anomeric configuration. Only the glucose bond is in the a-anomeric configuration. The conventional diagrams of glucose and fructose alone and in sucrose are illustrated in Fig. 15.6.

In aqueous solution, the monosaccharides generally adopt a ring structure, rather than having straight chains. Sketch representations for the ring forms of glucose and fructose. 

Emil Fischer, a German chemist, characterizes the structure of glucose, mannose, fructose, and arabinose... 

Monosaccharides belong to one of two families, namely aldoses or ketoses. Typical of these are the two structural isomers glucose and fructose (10.3). 

Studies on the action of acids on phosphoric esters are important in the determination of structures and for analytical purposes. Measurements of the rate of acid hydrolysis were carried out by Lohmann in studies of glucose and fructose phosphates and by Levene in his investigations on nucleotides. Since then they have been used routinely. 

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. 

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