Organic Chemistry 354 Quiz - November 29, 1999
Dr. Sundin
- 1. Optically active aldopentose A was strongly oxidized with
nitric acid to give optically inactive diacid B. Degradation of
A gave optically active aldotetrose C. Degradation of
C gave L-glyceraldehyde. Nitric acid oxidation of C gave
optically active diacid D. Give Fischer projections of A,
B, C, D, and D-glyceraldehyde.
Answer
- 2. Monosaccharides exist in the solid state as cyclic hemiacetals
and in water solution as an equilibrium mixture of cyclic hemiacetals
and the open chain free aldehyde or ketone. Shown below are two hemiacetals.
Which hemiacetal, A or B, is the hemiacetal of a ketose?
Answer
- 3. At first glance, one is surprised to find that ketoses can be
reducing sugars just like aldoses. However, upon remembering that the
Tollens’, Fehling’s, and Benedict’s tests are all done in a basic solution
and remembering the ease at which keto-enol tautomerization occurs in basic
solution, the reducing nature of sugars is explained with two tautomerizations,
ketose to enol followed by enol to aldose. Give Fischer projections of: a
D-ketohexose and the appropriate enol and resulting aldose obtained by
keto-enol tautomerization.
Answer
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