Concept explainers
(a)
Interpretation:
The acetal and hemiacetal in isomaltose should be labeled.
Concept Introduction:
In a hemiacetal, an alcohol and ether attached to the same carbon.
A hemiacetal with an alcohol forms an acetal.
(b)
Interpretation:
The monosaccharide ring should be numbered.
Concept Introduction:
Monosaccharides or simple sugars are the simplest carbohydrates. Generally, have three to six carbon atoms in a chain, with a carbonyl group at either the terminal carbon, numbered C1, or the carbon adjacent to it, numbered C2.
(c)
Interpretation:
Glycosidic linkage needs to be classified as a or β and its location should be designated using numbers.
Concept Introduction:
Disaccharides are carbohydrates composed of two monosaccharides.
Disaccharides are acetals, compounds that contain two alkoxy groups (OR groups) bonded to the same carbon.
A disaccharide results when a hemiacetal of one monosaccharide reacts with a hydroxyl group of a second monosaccharide to form an acetal. The new C-O bond that joins the two rings together is called a glycosidic linkage.
The two monosaccharide rings may be five-membered or six-membered. All disaccharides contain at least one acetal that joins the rings together. Each ring is numbered beginning at the anomeric carbon, the carbon in each ring bonded to two oxygen atoms
An a glycoside has the glycosidic linkage oriented down, below the plane of the ring that contains the acetal joining the monosaccharides.
A β glycoside has the glycosidic linkage oriented up, above the plane of the ring that contains the acetal joining the monosaccharides.
(d)
Interpretation:
Whether the hemiacetal drawn is n a or β anomer should be predicted.
Concept Introduction:
Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration of C-1 if they are aldoses or in the configuration at C-2 if they are ketoses. The epimeric carbon in anomers is known as anomeric carbon or anomeric center.
Depending on the orientation of carbon number 1 when the carbon number 5 hydroxyl bonds to it, two different forms can result.
These two forms are identical except for the configuration around C1. These two forms are called anomers.
C1 is called the anomeric carbon. If the hydroxyl group on C1 and the -CH2OH group on C5 are on opposite sides of the six-membered ring, C1 is known to be the α anomer.
If they are on the same side, C1 is known to be the β anomer.
(e)
Interpretation:
The monosaccharide formed, when isomaltose is hydrolyzed should be predicted.
Concept Introduction:
Disaccharides are carbohydrates composed of two monosaccharides.
Disaccharides are acetals, compounds that contain two alkoxy groups (OR groups) bonded to the same carbon.
A disaccharide results when a hemiacetal of one monosaccharide reacts with a hydroxyl group of a second monosaccharide to form an acetal. The new C-O bond that joins the two rings together is called a glycosidic linkage.
The two monosaccharide rings may be five-membered or six-membered. All disaccharides contain at least one acetal that joins the rings together. Each ring is numbered beginning at the anomeric carbon, the carbon in each ring bonded to two oxygen atoms.
The hydrolysis of a disaccharide cleaves the C-O glycosidic linkage and forms two monosaccharides.
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Chapter 20 Solutions
EBK GENERAL, ORGANIC, & BIOLOGICAL CHEM
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