1. Carbohydrates
Classification
Monosaccharides
Chiral Carbon Atoms
Structures of Important
Monosaccharides
Cyclic Structures
1

2. Carbohydrates
• Major source of energy from our diet
• Composed of the elements C, H and
O
• Produced by photosynthesis in
plants
2

3. Types of Carbohydrates
• Monosacchrides
• Disaccharides
Contain 2 monosacchride units
• Polysacchrides
Contain many monosacchride units
3

4. Monosacchrides
• Three Carbons = Triose
• Four Carbons = Tetrose
• Five Carbons = Pentose
• Six Carbons = Hexose
4

5. 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

6. Learning Check C1
Identify each as tetrose, pentose or
hexose, and as aldose or ketose
H
C O CH2OH
H C OH
C O
H C OH
HO C H
H C OH
H C OH
H C OH
CH2OH
CH2OH
A B 6

7. Solution C1
H
C O
CH2OH
H C OH
C O
H C OH
H C OH HO C H
H C OH H C OH
CH2OH CH2OH
A B
aldose, hexose ketose, pentose
7

8. Chiral Objects
• Chiral compounds have the same number
of atoms arranged differently in space.
• A chiral carbon atom has four different
groups attached
8

9. 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

10. Tetrahedral
carbon atom
bonded to four
different groups
10

11. ARE THERE CHIRAL C-ATOMS
IN THESE MOLECULES?
CH3CHClCH2CH3
A
CH2ClCH3
B
11

12. Learning Check C2
Determine if there is a chiral carbon in
each compound.
Cl Cl
H C CH 3 H C CH3
CH 2 CH 3 H
A B
12

13. Solution C2
Cl Cl
H C CH3 H C CH3
CH2CH3 H
A Yes, 4 different B No, the
groups are attached 2 H atoms
to the second C atom are identical
13

14. 14

15. Glyceraldehyde
15

16. 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.
16

17. D notation
O
H C
H C OH
H C OH
CH2OH
Right = D
17

18. Glucose
H
C O
H C OH
HO C H
H C OH
H C OH
CH2OH
D-Glucose
18

19. Fructose
CH2
OH
C O
HO C H
H C OH
H C OH
CH2OH
D-Fructose 19

20. Galactose
H O
C
H C OH
HO C H
HO C H
H C OH
CH2OH
D-galactose
20

21. 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
21

22. Haworth Structure for D-Isomers
The cyclic structure of a D-isomer has
the final CH2OH group located above the
ring.
CH2OH
o
22

23. Haworth Structure for D-
Glucose
• 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 α anomer, up
for β anomer
23

24. Cyclization of glucose
24

25. Haworth Structure for D-
Glucose
CH2OH CH2OH
o o OH β
OH OH
OH OH OH
α
OH OH
α-D-Glucose β-D-Glucose
25

26. d-fructose
26

27. Mutarotation
• Mutarotation: A small amount of open
chain is in equilibrium with the cyclic
forms.
• The most stable form of glucose is β-D-
glucose .
α-D-glucose D-glucose (open) β-D-glucose
(36%) (trace) (64%)
27

28. Learning Check C3
Write the cyclic form of α-D-galactose
H O
C
H C OH
HO C H
HO C H
H C OH
CH2OH 28

29. Solution C3
CH2OH
OH o
OH
OH
OH
α-D-galactose
29