CHEM 109C – Zhang
CLAS, F10
Carbohydrates II: Reactions - KEY
Don’t forget to know: fructose, ribose, glucose, galactose, mannose
1. Complete the following reactions
B. Reduction (only aldose to alditol); usually will see 1. NaBH4 2. H3O+
What other sugar can be reduced under the same conditions to form
D-mannitol? A C-2 ketose…
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CHEM 109C – Zhang
CLAS, F10
Carbohydrates II: Reactions - KEY
C. Oxidation (ONLY aldose to aldonic acid); loss of red-brown color of Br2
D. Strongest oxidation (aldoses, ketoses and primary OHs to form aldaric acid)
E. Oxidation (BOTH aldoses and ketoses to form aldonic acid); Tollen’s reagent
= Ag+, NH3, OH-
F. Osazone formation; requires xs or at least 3 equivalents of phenylhydrazine
C-2 epimers and the C-2 ketose will all form the same osazone
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CHEM 109C – Zhang
CLAS, F10
Carbohydrates II: Reactions - KEY
&
D-fructose
G. Kiliani-Fischer synthesis; increases length of C chain by 1 C (adds a C to C1) – KNOW MECH!
aldoheptoses, C-2 epimers
Wohl degradation; decreases length of C chain by 1 C (removes C-1 and you
lose one asymmetric center) – KNOW MECH!
A. Acetal/ketal formation (hemiacetal/ketal reacting with alcohol under
acidic conditions)
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CHEM 109C – Zhang
CLAS, F10
Carbohydrates II: Reactions - KEY
2. Label each of the following as a reducing or nonreducing sugar.
Reducing Sugars
Nonreducing Sugars
Can reduce an oxidizing agent (Ag+ or Br2)
Can NOT reduce an oxidizing agent (Ag+ or Br2)
Can be oxidized
Can NOT be oxidized
Straight chain sugars
Sugars w/out open able rings/NOT in
Sugars with open able rings/in equilibrium
equilibrium with the straight chain struct
with the straight chain struct (hemiacetals/ketals)
(acetal/ketals = glycosides, N-glycosides)
A, C, F, G, H
B, D, E, I, J
Ch 21 #26
b. hemiacetal
a. acetal
c. acetal
d. acetal
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