Chapter 24
Carbohydrates
Review of Concepts
Fill in the blanks below. To verify that your answers are correct, look in your textbook at
the end of Chapter 24. Each of the sentences below appears verbatim in the section
entitled Review of Concepts and Vocabulary.
newly created chirality center is called the ___________ carbon.
• In the α anomer, the hydroxyl group at the anomeric position is ______ to the
CH
2
OH group, while in the β anomer, the hydroxyl group is ______ to the
CH
2
OH group.
• Anomers equilibrate by a process called _____________, which is catalyzed by
yield an ___________.
• When treated with a suitable oxidizing agent, an aldose can be oxidized to yield
an __________.
• When treated with HNO
3
, an aldose is oxidized to give a dicarboxylic acid called
monosaccharides are converted into their corresponding N-glycosides.
640
CHAPTER 24
Review of Skills
Fill in the blanks and empty boxes below. To verify that your answers are correct, look
in your textbook at the end of Chapter 24. The answers appear in the section entitled
SkillBuilder Review.
24.1 Drawing the Cyclic Hemiacetal of a Hydroxyaldehyde
DRAW THE CYCLIC HEMIACETAL THAT IS FORMED WHEN THE FOLLOWING HYDROXYALDEHYDE
UNDERGOES CYCLIZATION UNDER ACIDIC CONDITIONS.
H
O
HO
[ H
+
]
24.2: Drawing a Haworth Projection of an Aldohexose
24.3: Drawing the More Stable Chair Conformation of a Pyranose Ring
DRAW THE MORE STABLE CHAIR CONFORMATION OF
α
–
D
-GALACTOPYRANOSE.
24.4 Identifying a Reducing Sugar
OH
CHAPTER 24
641
24.5 Determining Whether a Disaccharide Is a Reducing Sugar
Review of Reactions
Identify the reagents necessary to achieve each of the following transformations. To
verify that your answers are correct, look in your textbook at the end of Chapter 24. The
answers appear in the section entitled Review of Reactions.
Hemiacetal Formation
C
H O
1
6
CH
2
OH
C O
HHO
OHH
CH
2
OH
OHH
HOCH
2
H
OH H
H OH
OH
CH
2
OH
O
HOCH
2
CH
2
OH
OH
H
OH H
H
O
HO
1
2
3
4
5
6
1
2
3
4
5
6
Chain Lengthening and Chain Shortening
642
CHAPTER 24
Reactions of Monosaccharides
CH
2
OH
O
HO
HO OH
OH
CH
2
OAc
Solutions
24.1.
a) an aldohexose b) an aldopentose c) a ketopentose
d) an aldotetrose e) a ketohexose
24.4.
a)
C
OHH
OHH
OHH
OHH
CH
2
OH
H O
b)
C
HHO
HHO
HHO
HHO
CH
2
OH
H O
CHAPTER 24
643
24.5.
24.6.
24.7.
CH
2
OH
C O
HOH
24.8. D-fructose and D-glucose are constitutional isomers. Both have molecular formula
(C
6
H
12
O
6
). Although they have the same molecular formula, they have different
constitution – one is a ketone, and the other is an aldehyde.
644
CHAPTER 24
24.9.
a)
O
OH
b)
O OH
c)
O
OH
d)
OOH
24.11.
a)
O
OH
HO O OH
H
O
24.12.
a)
O
OH OH
OH
OH
HOCH
2
1
2
3
4
5
6
b)
O
OH OH
OH
OH
HOCH
2
1
2
3
4
5
6
c)
O
OH OH
OHOH
HOCH
2
1
2
3
4
5
6
24.13. β-D-galactopyranose
CHAPTER 24
645
24.14.
C
HHO
OH
AH
1
2
24.15.
C
HHO
HHO
HHO
OH
AH
1
2
3
4
5
6
6
24.16.
a)
O
OH
HO OH
OH
CH
2
OH
H
b)
O
HO
HO
OH
OH
CH
2
OH
H
c)
O
HO
HO
H
OH
CH
2
OH
OH
24.17.
C
OH
D
–
A
l
l
o
s
e
646
CHAPTER 24
24.18.
24.19.
a)
OH
OH OH
O
b)
OH
OH OH
O
c)
OH
OH
OH
O
d)
OH
OH
OH
O
24.20.
C
H O H O
H
C
H O HOH
H
OH
OH
OH
O
HOH
CHAPTER 24
647
24.21.
CH
2
OH
H
CH
2
OH
OH
24.22.
CH2OH
24.23.
a)
HO CH
2
OH
O
HO
OH
OH
excess Ac
2
O
AcOCH
2
OAc
O
AcO
O
A
c
OAc
py
648
CHAPTER 24
24.24.
a)
HO CH
2
OH
O
HO
OH
OH
excess CH
3
I
Ag
2
O
CH
3
OCH
2
OCH
3
O
CH
3
O
OCH
3
CH
3
O
24.25.
CH
2
OH
O
HO
OH
OH
CH
2
OH
O
HO
O
OH
CH
2
OH
O
HO
OH
H Cl
CH
2
OH
O
HO
OH
– H
2
O
HH
HOHO HO
HO
—————————————–————————————-—————————
CH
2
OH
O
HO
OH H
EtOH
CH
2
OH
O
HO
O
H
HEt
HO
HOEt
CH
2
OH
O
HO
OEt
OH
H
HO HO HO
CHAPTER 24
649
24.26.
CH
2
OH
O
HO
HO
OH H
CH
2
OH
O
HO
HO
O
H
HH
3
C
HO
CH
2
OH
O
HO
HO
OCH
3
OH
H
H A
24.27.
C
HHO
H O
C
OHH
H O
C
OHH
H O
24.28.
C
HHO
OHH
OHH
OHH
CH
2
OH
H O
H
2
O
NaBH
4
CH
2
OH
HHO
OHH
OHH
OHH
CH
2
OH
CH
2
OH
HHO
HHO
HHO
OHH
CH
2
OH
D-Altose
Rotate
180
650
CHAPTER 24
24.29.
C
OHH
OHH
OHH
OHH
CH
2
OH
H O
H
2
O
NaBH
4
CH
2
OH
OHH
OHH
OHH
OHH
CH
2
OH
CH
2
OH
HHO
HHO
HHO
HHO
CH
2
OH
D-Allose
Rotate
180
L-Allose
24.30. The following alditols are meso compounds, and are therefore optically inactive:
C
OHH
OHH
OHH
OHH
CH
2
OH
H O
H
2
O
NaBH
4
CH
2
OH
OHH
OHH
OHH
OHH
CH
2
OH
D-Allose
(meso)
24.31.
a) No (an acetal) b) Yes c) Yes
CHAPTER 24
651
24.32.
a)
D
–
G
a
l
a
c
t
o
n
i
c
a
c
i
d
C
OHH
HHO
HHO
OHH
CH
2
OH
OHO
b)
D
–
G
a
l
a
c
t
o
n
i
c
a
c
i
d
C
OHH
HHO
HHO
OHH
CH
2
OH
OHO
c)
D
–
G
l
u
c
o
n
i
c
a
c
i
d
C
OHH
HHO
OHH
OHH
CH
2
OH
OHO
d)
D
–
G
l
u
c
o
n
i
c
a
c
i
d
C
OHH
HHO
OHH
OHH
CH
2
OH
OHO
24.34.
a)
C
OHH
OHH
OHH
CH
2
OH
D-Ribose
H O
OHH
OHH
OHH
CH
2
OH
D
–
A
l
l
o
s
e
H OH
C
H O
OHH
OHH
OHH
CH
2
OH
D
–
A
l
t
o
s
e
HO H
C
H O
Fischer-Kiliani
+
652
CHAPTER 24
24.35.
24.36.
C
H O
C
H O
H O
24.37.
C
H O
H O
24.38.
C
HHO
OHH
OHH
CH
2
OH
D
–
A
r
a
b
i
n
o
s
e
H O
HHO
OHH
OHH
CH
2
OH
D
–
G
l
u
c
o
s
e
H OH
C
H O
Fischer- +
Wohl
Degradation Kiliani
HHO
OHH
OHH
CH
2
OH
D
–
G
l
u
c
o
s
e
H OH
C
H O
HHO
OHH
OHH
CH
2
OH
D
–
M
a
n
n
o
s
e
HO H
C
H O
24.39.
a) Yes, one of the anomeric positions bears an OH group.
24.40.
CH
2
OH
OH
OH
CH
2
OH
OH
24.41.
a)
CH
2
OH
O
HO
HO O
OH
CH
2
OH
O
HO OH
OH
NaBH
4
H
2
O
CH
2
OH
O
HO
HO O
OH
CH
2
OH
OH
HO OH
OH
c)
CH
2
OH
O
HO
HO O
OH
O
HO OH
OH
CH
2
OH
CH
3
OH
HCl
CH
2
OH
O
HO
HO OCH
3
OH
CH
2
OH
O
HO
HO
OCH
3
OH
+
24.42.
a) a D-aldotetrose b) an L-aldopentose c) a D-aldopentose
d) a D-aldohexose e) a D-ketopentose
24.43.
24.44.
654
CHAPTER 24
24.45.
a) D-Ribose
b) D-Arabinose
HHO
C
H O
24.46.
a)
O
OH
b)
OOH
c)
O
OH
24.47.
H
O
HO
24.48.
HCO
H
1
5
5
24.49.
a) epimers b) diastereomers c) enantiomers d) identical compounds
24.50.
C
OH
24.51.
C
H O
C
OHH
H O
R
C
OHH
H O
R
C
OHH
HHO
H O
R
S
CH
2
OH
C O
24.52.
C
OHH
OH
C
OHH
H O
C
HHO
OH
C
OHH
OH
24.53.
HOCH
2
6
HOCH
2
HOCH
2
24.54.
HO
HOCH
2
O
OH
OH
OH
24.55.
a) α-D-allopyranose
656
CHAPTER 24
24.56.
C
OHH
OH
C
OHH
H O
C
OHH
OH
24.57.
a)
O
CH
3
O
OCH
3
OCH
3
OCH
3
CH
2
OCH
3
b)
O
AcO
OAc
OAc
OAc
CH
2
OAc
24.58. The product is a meso compound
C
HO O
24.59.
C
OHH
OH
C
OHH
HO O
CHAPTER 24
657
24.60.
O
HO
OH
HO
equatorial
axial
24.61.
HO CH
2
OH
O
HO
OH
OH
CH
3
OCH
2
OCH
3
O
CH
3
O
OCH
3
excess CH
3
I
Ag
2
O
CH
3
OCH
2
OCH
3
O
CH
3
O OCH
3
OCH
3
+
CH
3
O
24.62.
a) diastereomers
b) same compound
24.63.
CH
2
OH
C O
CH
2
OH
C O
CH
2
OH
C O
CH
2
OH
C O
24.64.
C
OHH
OHH
OH
C
HHO
OHH
OH
658
CHAPTER 24
24.65.
C
OHH
OH
D
–
G
l
u
c
o
s
e
C
HHO
OH
D
–
M
a
n
n
o
s
e
COH
D
–
A
r
a
b
i
n
o
s
e
24.66.
C
OHH
OH
HCN
OHH
H OH
CN
OHH
HO H
CN
+
24.67.
a)
CH
2
OH
OHH
HHO
OHH
OHH
CH
2
OH
H O
24.68. D-Allose and D-Galactose
24.69.
a) This compound will not be a reducing sugar because the anomeric position is an acetal
CHAPTER 24
659
24.70.
a) CH
3
OH, HCl
24.71.
24.72.
a) D-Arabinose
24.73.
HO
HOCH
2
O
OH
OH
HOCH
2
O
OH
OH
OOH
24.74.
C
H O
CH
2
OH
24.75.
CH
2
OH
O
HO
HO
1
660
CHAPTER 24
24.76.
a) No, it is not a reducing sugar because the anomeric position has an acetal
group.
O
HO
HO O
OH
OH
OH
salicin
H
3
O
+
O
HO
HO
OH
OH
OH
O
HO
HO
OH
+
OH
OH
24.77.
O
HO
HO OH
OH
OH
H Cl O
HO
HO O
OH
OH
H
H– H
2
OO
HO
HO
OH
OH
24.78.
CH
2
OH
O
HO
HO
CH
2
OH
O
HO
HO N
+
H
CHAPTER 24
661
24.79.
N
HO
N
N
NH
2
N
N
O
H
24.80.
COH
HHO
OHH
OHH
CH
2
OH
COH
HHO
HHO
OHH
CH
2
OH
COH
OHH
OHH
OHH
CH
2
OH
COH
OHH
HHO
OHH
CH
2
OH
24.81.
HO H
H OH
HO O
O
HOCH
2
662
CHAPTER 24
24.82. In order for the CH
2
OH group to occupy an equatorial position, all of the OH
groups on the ring must occupy axial positions. The combined steric hindrance of
all the OH groups is more than the steric hindrance associated with one CH
2
OH
24.83.
H OH
H OH
H O
OH
OEt
24.84. Glucose can adopt a chair conformation in which all of the substituents on the
ring occupy equatorial positions. Therefore, D-glucose can achieve a lower
energy conformation than any of the other D-aldohexoses.
24.85.
OH
OH
CH
2
OH
C O
HHO
OHH
OHH
CH
2
OH
C O
HO H
CH
2
OH
HO H
H OH
CH
2
OH
HOH
OH
HHO
OHH
OHH
CH
2
OH
OH
H
OH
CH
2
OH
O
H OH
HHO
CH
2
OH
HOH
OH
C
HHO
OHH
HHO
HHO
CH
2
OH
OH
OH
O
OHH
HHO
HHO
CH
2
OH
OH
H
HOH
OH
OHH
HHO
HHO
CH
2
OH
OH
H
OH
HHO
OHH
OHH
CH
2
OH
O
H
C O
OHH
CH
2
OH
HO H
H OH
CH
2
OH
C O
OHH
HHO
HHO
CH
2
OH
H
OH
H
OH
C
OHH
HHO
OHH
OHH
CH
2
OH
OH
OH
OHH
CH
2
OH
HO
H OH
CH
2
OH
OH
HHO
CH
2
OH
HO
HO H
CH
2
OH
D-glucose
L-glucose
taut
taut
taut taut
664
CHAPTER 24
24.86. Compound X is a D-aldohexose that can adopt a β-pyranose form with only one
axial substituent. Recall that D-glucose has all substituents in equatorial positions, so
compound X must be epimeric with D-glucose either at C2 (D-mannose), C3 (D-allose),
24.87. Compound A is a D-aldopentose. Therefore, there are four possible structures to
consider (Figure 24.4).
When treated with sodium borohydride, compound A is converted into an alditol that
exhibits three signals in its
13
C NMR spectrum. Therefore, compound A must be D-
a)
HHO
CH
2
OH
OHH
D-Xylose
H OH
C
H O