Carbohydrates
Classification
Monosaccharides
Chiral Carbon Atoms
Structures of Important
Monosaccharides
Cyclic Structures
1
Carbohydrates
• Major source of energy from our diet
• Composed of the elements C, H and
O
• Produced by photosynthesis in
plants
2
Types of Carbohydrates
• Monosacchrides
• Disaccharides
Contain 2 monosacchride units
• Polysacchrides
Contain many monosacchride units
3
Monosacchrides
• Three Carbons =
Triose
• Four Carbons =
Tetrose
• Five Carbons =
Pentose
• Six Carbons =
Hexose
4
Monosacchrides
• Aldoses are monosacchrides with an
aldehyde group and many hydroxyl (-OH)
groups.
• Ketoses are monosacchrides with a
ketone group and many hydroxyl (-OH)
groups.
5
Learning Check C1
Identify each as tetrose, pentose or
hexose, and as aldose or ketose
H
C O
H C OH
H C OH
H C OH
H C OH
CH2OH
A
CH2OH
C O
HO C H
H C OH
CH2OH
B
6
Solution C1
H
C O
H C OH
H C OH
H C OH
CH2OH
C O
HO C H
H C OH
H C OH
CH2OH
CH2OH
A
aldose, hexose
B
ketose, pentose
7
Chiral Objects
• Chiral compounds have the same number
of atoms arranged differently in space.
• A chiral carbon atom has four different
groups attached
8
Mirror Images
• The three-dimensional structure of a chiral
compound has a mirror image.
• Your hands are chiral. Try to superimpose
your thumbs, palms, back of hands, and little
fingers. Is it possible? Why or why not?
9
Learning Check C2
Determine if there is a chiral carbon in
each compound.
Cl
Cl
C CH3
H
CH2CH3
A
H
C CH3
H
B
10
Solution C2
Cl
Cl
H
C CH3
CH2CH3
A Yes, 4 different
groups are attached
to the second C atom
H
C CH3
H
B No, the
2 H atoms
are identical
11
D and L Notation
• D,L tells which of the two chiral isomers
we are referring to.
• If the –OH group on the next to the bottom
carbon atom points to the right , the
isomer is a D-isomer; if it points left, the
isomer is L.
• The D form is usually the isomer found in
nature.
12
D notation
H C
O
H C OH
H C OH
CH2OH
Right = D
13
Glucose
H
C O
H C OH
HO C H
H C OH
H C OH
CH 2OH
D-Glucose
14
Fructose
CH 2OH
C O
HO C H
H C OH
H C OH
CH 2OH
D-Fructose
15
H
O
Galactose
C
H C OH
HO C H
HO C H
H C OH
CH2OH
D-galactose
16
Cyclic Structures
• Monosaccharides with 5-6 carbon
atoms form cyclic structures
• The hydroxyl group on C-5 reacts
with the aldehyde group or ketone
group
O
o
17
Haworth Structure for D-Isomers
The cyclic structure of a D-isomer has
the final CH2OH group located above the
ring.
CH2OH
o
18
Haworth Structure for DGlucose
• Write –OH groups on the right (C2,
C4) up
• Write –OH groups on the left (C3)
down
• The new –OH on C1 has two
possibilites: down for  anomer, up
for  anomer
19
Haworth Structure for DGlucose
CH2OH
CH2OH
o
o
OH
OH

OH
OH
OH
OH
-D-Glucose

OH
OH
-D-Glucose
20
Mutarotation
• Mutarotation: A small amount of open
chain is in equilibrium with the cyclic
forms.
• The most stable form of glucose is β-Dglucose .
-D-glucose
(36%)
D-glucose (open)
(trace)
β-D-glucose
(64%)
21
Learning Check C3
Write the cyclic form of -D-galactose
H
O
C
H C OH
HO C H
HO C H
H C OH
CH2OH
22
Solution C3
CH2OH
o
OH
OH
OH
OH
-D-galactose
23