CHEMISTRY 122
HW CH#12 CARBOHYDRATES
6, 10, 14, 18, 22, 24, 26, 28, 30, 36, 40, 4246, 48, 64, 72.
12-06
A carbohydrate is a polyhydroxyaldehyde or polyhydroxyketone, or a substance
that gives these compounds on hydrolysis.
12-10
D-glucose,
the most abundant hexose in the biological world, is also known as
dextrose.
10-14
The designations D and L refer to the configuration of the stereocenter farthest
from the aldehyde or ketone group on a monosaccharide chain. When the
monosaccharide chain is drawn as a Fischer projection, a D-monosaccharide has
the –OH on this carbon on the right; an L monosaccharide has it on the left.
10-18
Each carbon of a monosaccharide and a disaccharide has an oxygen atom that is
able to participate in hydrogen bonding with water molecules.
10-22
The designation  means that the –OH group on the anomeric carbon of a cyclic
hemiacetal is on the same side of the ring as the terminal –CH2OH group. The
designation  means that it is on the opposite side of the ring from the terminal –
CH2OH group.
10-24
No. The hydroxyl groups on carbon 2, 3, and 4 of -D-glucose are equatorial, but
the hydroxyl group on carbon 1 is axial.
10-26
First compare each Haworth projection with that of -D-glucose. Compound (a)
differs in configuration at carbon 3. Compound (b) differs in configuration at
carbons 2 and 3.
CH2OH
HH
(a)
H
HO
O
OH
H
H
OH OH
CH2OH
O
HH
OH
(b)
H HO
HO
H
OH H
CH2OH
HH
H
HO
OH
H CHO
OH OH
CH2OH
OH
HH
H HO CHO
HO
OH H
CHO
OH
OH
OH
OH
CH2OH
D-Allose
CHO
HO
H
H
OH
H
OH
OH
H
CH2OH
D-Altrose
H
H
H
H
10-28
During mutarotation, the  and  forms of a carbohydrate are converted to an
equilibrium mixture of the two anomers via the open chain form. Mutarotation
can be detected by observing the change in optical activity over time as the two
anomeric forms equilibrate.
10-30
The specific rotation of -L-glucose changes to -52.7°.
10-36
In reduction of the ketone group of D-fructose, the –OH group at carbon 2 may be
either on the right or the left in the Fischer projection.
CH2OH
CH2OH
CH2OH
C=O
HO
H
H
OH
NaBH
4
HO
H
HO
H
HO
H
+
H
OH
H
OH
H
OH
H
H OH
H
OH
OH
CH2OH
CH2OH
CH2OH
D-Mannitol
D-Fructose
D-Sorbitol
10-40
The anomeric carbons of both monosaccharide units in sucrose are involved in
forming the glycosidic bond; therefore sucrose is not in equilibrium with its open
chain form and does not mutarotate or oxidize. In maltose and lactose, one of the
monosaccharide units is in the cyclic hemiacetal form, which is in equilibrium
with the open chain form and, therefore, undergoes oxidation.
10-42
(a) Both monosaccharides are units of D-glucose.
(b) The glycosidic bond can be described as -1,1- or -1,1- depending on which
D-glucose unit you take as the reference.
(c) Trehalose is not a reducing sugar, because both anomeric carbons participate
in forming the glycosidic bond.
(d) Trehalose will not undergo mutarotation for the reason given in (c).
10-46
Glycogen is stored in roughly equal amounts in the liver and muscle tissue.
10-48
In their digestive systems, cattle have microorganisms that contain betaglucosidases. These enzymes catalyze the hydrolysis of the glycosidic bonds of
cellulose. We do not have these enzymes in our digestive systems.
10-64
D-Glucose
can be reduced to D-sorbitol by either sodium borohydride or catalytic
hydrogenation by with a transition metal and hydrogen.
CHO
CH2OH
H
OH
H
OH
NaBH
HO
H
4
HO
H
H
OH
H
OH
or Ni/H2
H
OH
H
OH
CH2OH
CH2OH
D-Glucose
D-Sorbitol
10-72
The formation of five- and six-membered rings is a favorable process. They are
also stable ring structures. The presence of alcohol hydroxyls and
ketone/aldehyde carbonyls in the same molecule promote the intramolecular
cyclization between a hydroxyl and a carbonyl, forming cyclic hemiacetals.