The pyranose form arises by closure to a six-membered cyclic hemiacetal, with the C-5hydroxyl group undergoing nucleophilic addition to the carbonyl. In the b-pyranose form ofD-xylose the anomeric hydroxyl group is up.The preferred conformation of b-D-xylopyranose is a chair with all the hydroxyl groupsequatorial.(d)L-Xylose is the mirror image of D-xylose.To construct the furanose form of L-xylose, the hydroxyl at C-4 needs to be brought into theproper orientation to form a fve-membered ring.The aanomeric hydroxyl group is up in the Lseries.(e)Methyl a-L-xylofuranoside is the methyl glycoside corresponding to the structure just drawn.(
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