This document provides information on carbohydrate chemistry including: - Monosaccharides are solids with sweet taste that are extremely soluble in water due to hydroxyl groups. - Carbohydrates exhibit isomerism including enantiomers, epimers, anomers, and aldose-ketose isomers. - Carbohydrates commonly exist as cyclic structures called pyranoses and furanoses which create new chiral centers.

2. CARBOHYDRATE
CHEMISTRY
BY Dr.Shamim Akram
AP Biochemistry AIMC
2

3. Monosaccharides
• Most monosaccharides have a sweet taste
(fructose is sweetest,173%sweeter than sucrose).
• They are solids at room temperature.
• They are extremely soluble in water:
• Despite their high molecular weights, the
presence of large numbers of OH groups make
the monosaccharides much more water soluble
than most molecules of similar MW.
• Glucose can dissolve in minute amounts of water
to make a syrup (1 g / 1 ml H2O).

4. Sugar Relative Sweetness Type
• Lactose 0.16 Disaccharide
• Galactose 0.22 Monosaccharide
• Maltose 0.32 Disaccharide
• Xylose 0.40 Monosaccharide
• Glucose 0.74 Monosaccharide
• Sucrose 1.00 Disaccharide
•
• Fructose 1.73 Monosaccharide

5. NOMENCLATURE
• Asymmetric C (Chiral C):
• Carbon atom to which 4 different atoms
or moleculs are attached e.g.C no. 2-5
in glucose.
• Anomeric C:
• Carbon atom that is part of functional
group e.g.Aldehyde/Keton gp. C in
glucose &fructose.
5

6. 6
• Penultimate C:
• Carbon atom that is Farthest from functional
group e.g.C no. 5 in glucose molecule.
• Acetal/Ketal C:
• A new asym.C atom is created as anomeric
C is replaced by acetal/ketal C in soln. form
• Functional group:
• All physical and chemical properties of a
molecule depend on this gp
• Straight Chain .

7. ISOMERISM
ENANTIOMER OPTICAL EPIMER
ISOMER
ANOMER ALDOSE-KETOSE
ISOMER

8. The Stereochemistry of
Carbohydrates
• Two Forms of Glyceraldehyde
•Glyceraldehyde, the simplest
carbohydrate, exists in two isomeric forms
that are mirror images of each other:
10

9. Stereoisomers
• These forms are stereoisomers of each
other.
• Glyceraldehyde is a chiral molecule
— it cannot be superimposed on its
mirror image. The two mirror-image
forms of glyceraldehyde are
enantiomers of each other.• 11

10. Chirality and Handedness
• Chiral molecules have the same relationship
to each other that your left and right hands
have when reflected in a mirror.
10

11. Chiral Carbons
• Chiral objects cannot be superimposed on their
mirror images —e.g., hands, gloves, and shoes.
• Achiral objects can be superimposed on the mirror
images —e.g., drinking glasses, spheres, and
cubes.
• Any carbon atom which is connected to four
different groups will be chiral, and will have two
nonsuperimposable mirror images; it is a chiral
carbon or a center of chirality.
• –If any of the two groups on the carbon are the
same, the carbon atom cannot be chiral.
• Many organic compounds, including carbohydrates,
contain more than one chiral carbon.

12. Van’t Hoff’s 2n rule
When a molecule has more than one chiral carbon,
each carbon can possibly be arranged in either the
right-hand or left-hand form, thus if there are n
chiral carbons, there are 2n possible stereoisomers.
Maximum number of possible stereoisomers = 2n
Can you tell no. of possible stereoisomers of
CHOLESTEROL?

13. D and L isomers (Enantiomers)
Enantiomers :
They are the mirror image of each others.
CHO CHO
H - C– OH HO-C-H
CH2OH CH2OH
D-Glyceraldehyde L-Glyceraldehyde

14. Diastereoisomers
• The term diastereomers is used to represent the stereoisomers that
are not mirror images of one another.
• Configurational changes with regard to C2 , C3 and C4 will produce
eight different monosaccharides.
Total D + L forms = 16 isomers of glucose

16. 16
Carbohydrates are designated as D- or L- according to the
stereochemistry of the highest numbered chiral carbon of the
Fischer projection. If the hydroxyl group of the highest numbered
chiral carbon is pointing to the right, the sugar is designated as
D (Dextro: Latin for on the right side). If the hydroxyl group is
pointing to the left, the sugar is designated as L (Levo: Latin for
on the left side). Most naturally occurring carbohydrates are of
the D-configuration.
CHO
HO H
H OH
HO H
HO H
CH2OH
L- glucose
H
CHO
OH
HHO
OHH
OHH
CH2OH
D-Glucose
1
CHO
OHH
HHO
HHO
CH2OH
L-Arabinose
1
highest numbered
"chiral" carbon
highest numbered
"chiral" carbon
2
3
4
56
4
5
3
2
CHO
HO H
H OH
H OH
CH2OH
D-Arabinose
highest numbered
"chiral" carbon
highest numbered
"chiral" carbon

17. What’s So Great About Chiral
Molecules?
•Molecules which are enantiomers of each
other have exactly the same physical
properties (melting point, boiling point,
index of refraction, etc.) but not their
interaction with polarized light.
••Polarized light vibrates only in one plane;
it results from passing lights through
polarizing filter

19. Optical Activity
•A levorotatory(–) substance rotates polarized light to the left
[e.g., l-glucose; (-)-glucose].
••A dextrorotatory(+) substance rotates polarized light to the
right [e.g., d-glucose; (+)-glucose].
••Molecules which rotate the plane of polarized light are
optically active.
••Many biologically important molecules are chiral and
optically active. Often, living systems contain only one of the
possible stereochemical forms of a compound, or they are
found in separate system.
•–D-lactic acid is found in living muscles; D-lactic acid is present in sour milk.
•–In some cases, one form of a molecule is beneficial, and the enantiomer is a poison (e.g.,
thalidomide).
•–Humans can metabolize D-monosaccharides but not L-isomers; only L-amino acids are used
in protein synthesis

20. Aldopentoses and Aldohexoses.
Aldopentoses: C5, three chiral carbons, eight stereoisomers
Aldohexoses: C6, four chiral carbons, sixteen stereoisomers
CHO
OHH
OHH
OHH
CH2OH
D-ribose
CHO
HHO
OHH
OHH
CH2OH
CHO
OHH
HHO
OHH
CH2OH
CHO
HHO
HHO
OHH
CH2OH
D-arabinose D-xylose D-lyxose

21. 21

22. 22
In the case of carbohydrates, cyclization to the hemiacet
creates a new chiral center.
Converting Fischer Projections to Haworth formulas
CHO
OHH
OHH
CH2OH
H
OH
H
H
OH OH
H H
O
OH
H
H
H
OH OH
H H
O
**
*
D-erythrose
+

23. 23

24. 24

25. 25
In the case of carbohydrates, cyclization to the hemiacet
creates a new chiral center.
Converting Fischer Projections to Haworth formulas
CHO
OHH
OHH
CH2OH
H
OH
H
H
OH OH
H H
O
OH
H
H
H
OH OH
H H
O
**
*
D-erythrose
+

26. Pyranoses and Furanoses

27. 27
Cyclic Forms of Carbohydrates: Pyranose Forms.
glucopyranose
ribopyranose
CHO
OHH
OHH
OHH
HH
OH
D-ribose
OH
H
OHHO
HO
O
CHO
OH
H
OH
HH
OH
H
H
HO
H
H H
H
H
OH
O
OHHO
HO
HH
H H
H
H
OH
HO
H
OH
H
OHOH
H
H
H
OH
HO
OH
H
H
OHOH
H
H
H
new chiral
center
1
3
4
5
1 1
11
2
2
2 2
1
3
33 2
3
3
4
4
4 4
4
5
5
5
5
5
CHO
OHH
HHO
OHH
HHOH2C
OH
D-glucose
OH
H
OHH
HO
O
CHO
OH
H
H
OHH
OH
HOH2C
H
HO
H
OH H
CH2OH
H
OH
O
OHH
HO
HH
OH H
CH2OH
H
OH
HO
H
OH
H
OHH
OH
CH2OH
H
OH
HO
OH
H
H
OHH
OH
CH2OH
H
new chiral
center
1
3
4
5
6
1 1
11
2
2
2 2
1
3
33 2
3
3
4
4
4 4
4
5
5
5
5
5
6
6
6
6
6

28. Two types of pyranose form
(HAW0RTHs FORMULAS}
Chair form Boat form
28

29. MUTAROTATION
• Freshly prepared soln.of α-D glucose or
β-D glucose observed in polarimeter,its
sp. rotation go on changing then after
some time it is fixed at 52.7,this
property of sugsrs is mutarotation
29

30. 30
Mutarotation and the Anomeric Effect. The hemiacetal
or hemiketal carbon of the cyclic form of carbohydrates is the
anomeric carbon. Carbohydrate isomers that differ only in the
stereochemistry of the anomeric carbon are called anomers.
Mutarotation: The - and -anomers are in equilibrium, and
interconvert through the open form. The pure anomers can be
isolated by crystallization. When the pure anomers are dissolved
in water they undergo mutarotation, the process by which they
return to an equilibrium mixture of the anomer.
-D-Glucopyranose (36%)
(-anomer: C1-OH and
CH2OH are trans)
-D-Glucopyranose (64%)
(-anomer: C1-OH and
CH2OH are cis)
O
HO
HO
HOH2C
HO
OHCHO
OHH
HHO
OHH
OHH
CH2OH
OH
H
HO
HO
HO
HOH2C
O
H
OH
H
HO
HO
HO
HOH2C
O
O
HO
HO
HOH2C
HO
H
OH
D-glucose
Trans
Cis

31. 31
α, D-glucose  D-glucose  , D-glucose
(+110 ) (+52.5) (+17.2 )

32. Epimers:
• Two monosaccharides differ only in the
configuration around one specific carbon
atom.
• The D-glucose and D-mannose are
epimers with respect to carbon atom 2,
• D-glucose and D-galactose are epimers
with respect to carbon atom 4.

34. Aldose-Ketose isomerism:
Two monosaccharides have the same
molecular formulae but differ in their
functionl groups.
• one has an aldehyde group (aldose e.g.
glucose)
• the other has a ketone group (Ketose e.g.
fructose).