Concept explainers
(a)
Interpretation:
The glycosidic linkage and acetal carbon in the lactose are to be identified.
Concept introduction:
An acetal is characterized by a C atom bonded to two alkyl (or H) groups and two alkoxy (RO–) groups. The compound in which the OH from a sugar molecule has been replaced by OR is called glycoside. The
(b)
Interpretation:
The type of glycosidic linkage that lactose has is to be determined.
Concept introduction:
If the alkoxy (RO-) group on the acetal carbon is in axial position, it is designated as
(c)
Interpretation:
The complete, detailed mechanism and the products of the acid catalyzed hydrolysis of lactose are to be drawn.
Concept introduction:
The acid catalyzed hydrolysis of lactose gives two monosaccharides, which are linked by glycoside linkage. In Step 1, protonation of electron rich O atom takes place. The bond of acetal carbon and electron poor O of the glycosidic linkage breaks in heterolysis step. In Step 3, the newly formed carbocation is attacked by water as a nucleophile. This can take place on either side of the plane of the carbocation C. Finally, in Step 4, deprotonation removes the positive charge from O and forms
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ORGANIC CHEMISTRY E-BOOK W/SMARTWORK5
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