Announcements & Agenda (04/09/07)
Extra Credit Assignment Due NOW!
Pick Up Graded Quizzes
Quiz Friday (13.4, 13.5, & Ch 14)
Today
 More on Carbohydrates (14.1-14.3)
Monosaccharides
Cyclic Monosaccharides


Reactions of carbohydrates
Disaccharides
1
Last Time: Amide Hydrolysis
acid hydrolysis
O
||
CH3—C—NH2
O
||
CH3—C—OH + NH4+Cl–
HCl + H2O
NaOH
O
||
CH3—C—O– Na+ + NH3
base hydrolysis
2
Last Time: Carbohydrates Intro
• a major source of
energy from our diet
• composed of C, H, & O
• also known as
saccharides, which
means “sugars.”
3
Last Time: Types of Carbohydrates
• Monosaccharides: simplest carbohydrates.
• Disaccharides: consist of two monosaccharides.
• Polysaccharides: contain many monosaccharides.
4
Last Time: Monosaccharides
• typically 3-6 carbon atoms
• have a C=O group (aldehyde or ketone)
•
•
aldoses
ketoses
• several hydroxyl groups
5
Aldoses
• monosaccharides with an
aldehyde group…
• …and many hydroxyl
groups.
triose
(3C atoms)
tetrose (4C atoms)
pentose (5C atoms)
hexose (6C atoms)
O
║
C─H aldose
│
H─ C─OH
│
H─ C─OH
│
CH2OH
Erythose
6
Ketoses
CH2OH
• monosaccharides with a
│
ketone group…
C=O
ketose
• …and many hydroxyl
│
groups.
H─ C─OH
│
H─ C─OH
│
H─C─OH
│
Fructose, a ketohexose
CH2OH
7
Fischer Projections
• also used to represent carbohydrates.
• places the most oxidized group at the top.
• shows chiral carbons as the intersection of
vertical and horizontal lines.
8
D & L Notations: Know This Now…
In a Fischer projection, the −OH group on the
• chiral carbon farthest from the carbonyl group
determines an L or D isomer.
• left = L for the L-form.
• right = D for the D-form. (MOST COMMON IN
NATURE!)
9
Learning Check
Identify each as the D or L isomer.
A.
B.
C.
CH2OH
O
C H
HO
H
HO
H
H
HO
H
HO
CH2OH
L
__-Ribose
O
O
C H
HO
H
OH
H
OH
H
H
OH
CH2OH
L Threose
__-
CH2OH
D Fructose
__10
D-Glucose
• found in fruits, corn
syrup, and honey
• an aldohexose with
the formula C6H12O6
• known as blood
sugar in the body
• the monosaccharide
in polymers of
starch, cellulose,
and glycogen
11
Blood Glucose Level
In the body,
• normal blood: [glucose] = 70-90 mg/dL.
• a glucose tolerance test measures blood
glucose for several hours after ingesting
glucose.
12
D-Fructose
• is a ketohexose
C6H12O6
• is the sweetest
carbohydrate
• found in fruit
juices and honey
• converts to
glucose in the
body
CH2OH
C O
HO C H
H C OH
H C OH
CH2OH
D-Fructose
13
D-Galactose
• is an aldohexose
C6H12O6.
• not found free in nature.
• is obtained from lactose,
a disaccharide.
• has a similar structure to
glucose except for the
–OH on C4
Which C is C4???
O
C H
H C OH
HO C H
HO C H
H C OH
CH2OH
D-Galactose
14
Cyclic Structures (14.3)
• prevalent form of monosaccharides with 5
or 6 carbon atoms
O
O
• form when the hydroxyl group on C-5
reacts with the aldehyde group or ketone
group
•
Orgo-Chem reaction not previously mentioned:
“C=O” + ROH → hemiacetal
15
Drawing Cyclic Structures: Practice!
Example: Glucose
STEP 1 Number the carbon chain and turn
clockwise to form a linear open chain.
H O
C
1
H 2 C OH
HO 3 C H
H 4 C OH
H
5C
OH
H
H OH H
O
HOCH2 C C C C C
6
5
4
3
2
1
H
OH OH H OH
6 CH OH
2
16
Cyclic Structure for Glucose
STEP 2 Fold into a hexagon.
• Bond the C5 –O– to C1.
• Place the C6 group above
the ring.
• Write the –OH groups on C2
& C4 below the ring (These
are the C atoms that pointed
down from Step 1).
• Write the –OH group on C3
above the ring.
• Write a new –OH on C1.
CH2OH
6
5
O
4
OH
1
OH
3
2
OH
OH
17
Cyclic Structure for Glucose
STEP 3 Write the new –OH on C1
• down for the  form.
• up for the  form.
CH2OH
O
OH
OH
O
OH
OH
-D-Glucose

CH2OH

OH
OH
OH
OH
-D-Glucose
18
Summary of the Formation of
Cyclic Glucose
19
Mutarotation
• cyclic structures open and close.
• -D-glucose converts to β-D-glucose & vice versa.
• at any time, only a small amount of open chain forms.
CH2OH
CH2OH
O
OH
H
O
OH
OH
OH
OH
-D-glucose
(36%)
CH2OH
O
O
C
OH
H
OH
D-glucose (open)
(trace)
OH
OH
OH
OH
β-D-glucose
(64%) 20
Cyclic Structure of Fructose
• is a ketohexose.
• reacts the -OH on C-5 with the C=O on C-2
CH2OH
C O
CH2OH
HO C H
CH2OH
OH
H C OH
H C OH
CH2OH
O
O
OH
OH
OH
CH2OH
OH
OH
α-D-fructose
-D-fructose
CH2OH
D-fructose
21
Chemical Properties of
Monosaccharides (14.4)
22
Reducing Sugars
• are monosaccharides that oxidize to give
a carboxylic acid.
• undergo reaction in the Benedict’s test.
• include the monosaccharides glucose,
galactose, and fructose.
23
Oxidation of D-Glucose
O
O
C
H
C OH
H C OH
H C OH
[O]
HO C H
H C OH
+ Cu
2+
HO C H
H C OH
H C OH
H C OH
CH2OH
CH2OH
D-glucose
+ Cu2O(s)
D-gluconic acid
QUESTION: WHY CAN FRUCTOSE (A KETONE) BE OXIDIZED???
ANSWER: ISOMERIZATION TO AN ALDEHYDE…
24
One Test for Glucose in Urine:
Benedict’s Test
25
Reduction of Monosaccharides
• involves the
carbonyl group.
• produces sugar
alcohols, or
alditols.
• such as Dglucose gives
D-glucitol also
called sorbitol.
D-Glucitol
26
Learning Check
Write the products of the oxidation and
reduction of D-mannose.
O
C H
HO
H
HO
H
H
OH
H
OH
CH2OH
D-mannose
27
Solution
CH2OH
HO
H
HO
H
Reduction
O
O
C H
C OH
HO
H
HO
H
Oxidation
HO
H
HO
H
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
CH2OH
D-mannitol
CH2OH
CH2OH
D-mannose
D-mannonic acid
28
Disaccharides (14.5)
29
Important Disaccharides: Know These 3
A disaccharide consists of two monosaccharides.
Monosaccharides
Disaccharide
glucose + glucose
maltose + H2O
glucose + galactose
lactose + H2O
glucose + fructose
sucrose + H2O
30
Maltose
Free α-OH
A.K.A. “malt sugar”
obtained from starch
hydrolysis
used in cereals,
candies, and brewing
linked by an -1,4glycosidic bond formed
from the  −OH on C1
of the 1st glucose and
−OH on C4 of the 2nd
glucose
found in both the and β - forms
31
Lactose
• a disaccharide of
β-D-galactose
and α- or β-Dglucose.
• contains a β -1,4glycosidic bond.
• is found in milk
and milk products.
α-form
α-form
32
Sucrose
Sucrose or table sugar
• is obtained from sugar cane and sugar beets.
• consists of α-D-glucose and β-D-fructose..
• has an α,β-1,2-glycosidic bond.
α-D-glucose
β -D-fructose
33
Learning Check
Write the structures of the two
monosaccharides that form when sucrose
is hydrolyzed.
34
Solution
35