This document discusses carbohydrate classification and structures. It notes that carbohydrates are composed of carbon, hydrogen, and oxygen and are a major energy source. There are three types: monosaccharides, disaccharides, and polysaccharides. Monosaccharides can be classified as aldoses or ketoses depending on whether they contain an aldehyde or ketone group. Many monosaccharides form cyclic structures with 5-6 carbons through a reaction between a hydroxyl group and aldehyde/ketone. Common monosaccharides like glucose and fructose form specific cyclic structures called Haworth structures depending on whether they are in the alpha or beta configuration.

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