Ring structure, of glucose

Figure 9.7 Six- and five-membered cyclic ethers. The stable ring structures which are adopted by hexoses and pentoses are five- or six-membered and contain an oxygen atom. They are named as derivatives of furan or pyran, which are the simplest organic compounds with similar ring structures, e.g. glucofuranose or glucopyranose for five-or six-membered ring structures of glucose respectively.

Figure 4.3 (a) Ring structure of glucose showing the true bond angles, (b) Ring structure of glucose... 

Another method for the establishment of the ring structures of glucose (and other sugars) involves the correlation of the optical rotations of the sugars with those of the glycosides. This method, although not absolute, was developed and widely applied by C. S. Hudson and has much value for this purpose. It is considered in a later section (p. 70). 

The 3,6-anhydro-D-glucose (XIX) of Fischer and Zach13 on reduction with sodium amalgam or with hydrogen in the presence of Raney nickel14 gives 3,6-anhydro-D-sorbitol (XX), a method of synthesis which establishes the ring structure of the substance since that of 3,6-anhydro-D-... 

Using methods similar to Fischer s, the straight-chain form of any monosaccharide can be worked out. As we have seen, however, monosaccharides exist mostly as cyclic pyra-nose or furanose hemiacetals. These hemiacetals are in equilibrium with the open-chain forms, so sugars can react like hemiacetals or like ketones and aldehydes. How can we freeze this equilibrium and determine the optimum ring size for any given sugar Sir Walter Haworth (inventor of the Haworth projection) used some simple chemistry to determine the pyranose structure of glucose in 1926. 

Note It is normal in writing the ring structures of sugars to omit the H atoms attached to carbon, in which case /3-D-glucose is written as ... 

Freudenberg and co-workers showed that cyclodextrins have a ring structure of a(l— 4)-linked glucose units with a central cavity [10, 11]. During this period the basic structural and physicochemical properties of a-, P-, and y-cyclodextrin were described [12]. The enzymatic production of CDs was also investigated. 

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. 

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. 

Draw the Fisher (open-chain) structures and the most common Haworth (ring) structures of D-glucose, D-fructose, D-galactose, and D-ribose. 

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