Dolbier HW Solutions 624

Dolbier HW Solutions 624 - 718 CARBOHYDRATES Three...

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Three stereogenic centers occur in the furanose form, namely, the anomeric carbon C-1 and the original stereogenic center C-2, as well as a new stereogenic center at C-3. In addition to the two furanose forms just shown, two more are possible. Instead of the reaction of the CH 2 OH group that was shown to form the cyclic hemiacetal, the other CH 2 OH group may add to the aldehyde carbonyl. 25.25 The most reasonable conclusion is that all four are methyl glycosides. Two are the methyl glycosides of the a - and b -pyranose forms of mannose and two are the methyl glycosides of the a - and b - furanose forms. In the case of the methyl glycosides of mannose, comparable amounts of pyranosides and furano- sides are formed. The major products are the a isomers. 25.26 ( a ) Disaccharides, by de f nition, involve an acetal linkage at the anomeric position; thus all the
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