Aldohexoses structures

C is correct. Step 2 removes the top carbon from each structure and places a CH2OH group group at both ends of the new, 5-carbon structures. When looking at the original 8 aldohexose structures, you should nolice that molecules 1 2 are epimers with respect to carbon 2 3 4 are epimers with respect to carbon 2 5 6 are epimers with respect to carbon 2, and 7 8 are epimers with respect to carbon 2. Since the treatment of step... 

Problem 34.4 Treatment of (+)-glucpsc with HIO4 gives results that confirm its aldohexose structure. What products should be formed, and how much HIO4 should be consumed ... 

Ans. There are 2 or 16 stereoisomers since the aldohexose structure (see Problem 18.3) has four stereocenters, none of which have the same set of four different substituents. Eight of the stereoisomers are shown as the bottom horizontal row of structures in Fig. 18-1. The other eight stereoisomers are the mirror images of the o-family stereoisomers. 

Louis Fieser of Harvard University suggested the following procedure for remembering the names and structures of the eight o aldohexoses ... 

The following structure is that of an l aldohexose in its pyranose form. Identify it, and tell whether it is an a or 0 anomer. 

The c.d. spectra of glycuronic acids have been measured in a number of laboratories. " These sugar derivatives, named after the corresponding aldohexose, have the exocyclic hydroxymethyl group on C-5 replaced by the carboxyl chromophore. The structure of /3-D-mannopyranuronic acid is given as an example in formula 9, and the structures of the parent compounds in Fig. 1. 

From a structural point of view, the carbohydrate template can have either furan or pyran rings although in some cases open chain structures can be formed. A large variety of aldopentoses (e.g. d- and L-arabinose, D-ribose, D-xylose), aldohexoses (e.g. D-glucose, D-mannose, D-galactose) as well as ketohexoses (e.g. D-fructose, L-sorbose) can be used as scaffolds. 

Figure 9.5 Cyclic, hemiacetal structures of D-glucose. The reaction between an alcohol and aldehyde group within an aldohexose results in the formation of a hemiacetal. The only stable ring structures are five- or six-membered. Ketohexoses and pentoses also exist as ring structures due to similar internal reactions.

It follows that, when we dissolve a sugar such as glucose or ribose in water, we create a mixture of various equilibrating structures. The relative proportions of pyranose and furanose forms, and of their respective anomers for the eight aldohexoses, are shown in Table 12.1. In each case, the proportion of non-cyclic form is very small (<1%). 

Problem 22.57 (a) Write shorthand open structures for a ketohexose (I) and an aldohexose (II) which form the same osazone as D-(-)-altrose (III), the C epimer of o-mannose, and for the aric acid (IV) formed by HNOj oxidation of the o-aldohexoses (III) and o-talose (V). (b) Write shorthand and conformational structures for -D-altropyranose (VI). ... 

An aldopentose (A) of the D-configuration on oxidation with concentrated nitric acid gives a 2,3,4-trihydroxypentanedioic acid (a trihydroxyglutaric acid) (B) which is optically inactive. (A) on addition of HCN, hydrolysis, lactonization, and reduction gives two stereoiso-meric aldohexoses (C) and (D). (D) on oxidation affords a 2,3,4,5-tetrahydroxy-hexanedioic acid (a saccharic acid) (E) which is optically inactive. Give structures of compounds (A)-(E). 

The fragments of the C series expected have the same structures and m/e values as in the spectra of pentoses, and are shifted 72 mass units (the difference between H and CH OCOCH ) to lower m/e values compared with those of isomeric aldohexoses. This feature may also serve to dis-... 

The common six-carbon sugars (hexoses) are D-glucose, D-fructose, D-galactose, and D-mannose. They all are aldohexoses, except D-fructose, which is a ketohexose. The structures of the ketoses up to Cf) are shown for reference in Figure 20-2. The occurrence and uses of the more important ketoses and aldoses are summarized in Table 20-1. 

Fig. 5. Haworth formula indicating structural and configurational features essential for efficient binding of aldohexoses with glucose-6-phosphatase. From Lygre and Nordlie (126). Copyright (1965), Elsevier Publishing Co. Reproduced by permission.

D-Mannose, an aldohexose found in orange peels, has the following structure in open-chain form. Coil mannose around, and draw it in cyclic a and fi forms. 

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