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How to tell the difference between D and L isomers:
When the hydroxyl group on the reference carbon is on the right (dextro) in a projection formula that has the carbonyl carbon at the top, the sugar is the D isomer; when on the left(levo), it is the L isomer.
How to build up the name of a disaccharide:
By convention, the name describes the compound written with its nonreducing end to the left, and we can “build up” the name in the following order. (1) Give the configuration (α or β) at the anomeric carbon joining the first monosaccharide unit (on the left) to the second. (2) Name the nonreducing residue; to distinguish five-and six-membered ring structures, insert “furano” or “pyrano” into the name. (3) Indicate in parentheses the two carbon atoms joined by the glycosidic bond, with an arrow connecting the two numbers; for example, (1 → 4) shows that C-1 of the first-named sugar residue is joined to C-4 of the second. (4) Name the second residue. If there is a third residue, describe the second glycosidic bond by the same conventions.
How many stereoisomers does a molecule with n chiral centers have?
What is a reducing end? Can you identify the reducing end of a sugar? What is a reducing sugar?
- Reducing end: The end of a polysaccharide having a terminal sugar with a free anomeric carbon; the terminal residue can act as a reducing sugar.
- Reducing sugar: A sugar in which the carbonyl (anomeric) carbon is not involved in a glycosidic bond and can therefore undergo oxidation.
Why are single-headed arrows used? why double-headed arrows in naming a carbohydrate?
Single-headedarrows are used for disaccharides that have a free anomeric carbon, reducing end. Double headed arrows connect the anomeric carbons in the non-reducing disaccharides.
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