CARBOHYDRATE | classification Of carbohydrates

Carbohydrates Definition | Glucose and Fructose Structure And Process Of Formation | Type of Carbohydrates

1. DR. S. K. VERNWAL
Head, Chemistry Department
Maharana Pratap P. G. College
Jungle Dhusan, Gorakhpur

2. CHAPTER – 1

Carbohydrates
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

3. Carbohydrates are defined as polyhydroxy
aldehydes or polyhydroxy ketones or the
compounds which give these on hydrolysis and
contain atleast one chiral carbon atom.
Eg. Glucose, Fructose, Starch, Cellulose etc.
Carbohydrates are also known as saccharides.
Carbohydrates are widely distributed in plant
kingdom and play a vital role in our daily life.
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR
Carbohydrates

4. Carbohydrates are classified into
following three main classes.

1. Monosaccharides

2. Oligosaccharides

3. Polysaccharides

Classification of Carbohydrates
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

5. These are the simplest carbohydrates
which can not be further hydrolysed to
smaller molecules.
The general formula of monosaccharides
is (CH
2
O)
n
, where n = 3 - 6.
Eg. Erythrose (C
4
H
8
O
4
), ribose (C
5
H
10
O
5
),
glucose (C
6
H
12
O
6
), fructose (C
6
H
12
O
6
) etc.
1. Monosaccharides
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

6. These are the carbohydrates which give a
definite number (2-10) of monosaccharides
upon hydrolysis.
Depending upon the number of
monosaccharide molecules produced upon
hydrolysis, oligosaccharides are further
classified as disaccharides, trisaccharides,
tetrasaccharides etc.
2. Oligosaccharides
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

7.  Disaccharides: These are the carbohydrates
which give two molecules of same or
different monosaccharides upon hydrolysis.
Eg. Sucrose (C
12
H
22
O
11
), Lactose
(C
12
H
22
O
11
) etc.
C
12
H
22
O
11
+ H
2
O → C
6
H
12
O
6
+ C
6
H
12
O
6

Sucrose Glucose Fructose
H
+
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

8.  Trisaccharides: These are the
carbohydrates which give three molecules
of same or different monosaccharides upon
hydrolysis.
Eg. Raffinose (C
18
H
32
O
16
).
C
18
H
32
O
16
+2H
2
O → C
6
H
12
O
6
+ C
6
H
12
O
6
+ C
6
H
12
O
6

Raffinose Glucose Fructose Galactose
H
+
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

9.  Tetrasaccharides: These are the
carbohydrates which give four molecules of
same or different monosaccharides upon
hydrolysis.
Eg. Stachyose (C
24
H
42
O
21
).
C
24
H
42
O
21
+ 3H
2
O → C
6
H
12
O
6
+ C
6
H
12
O
6
+ 2C
6
H
12
O
6

Stachyose Glucose Fructose Galactose
H
+
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

10. These are the carbohydrates which give
a large number of monosaccharide molecules
upon hydrolysis.
The general formula of polysaccharides
is (C
6
H
10
O
5
)
n
where n>100. Eg. Starch,
Cellulose, Glycogen etc.
(C
6
H
10
O
5
)
n
+ (n-1) H
2
O → n C
6
H
12
O
6

Starch Glucose
H
+
3. Polysaccharides
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

11. Carbohydrates are further classified as
sugars and non sugars.
The carbohydrates which are sweet in
taste, crystalline in nature and readily soluble
in water are called as sugars.
Eg. Glucose, Fructose, Sucrose, Lactose etc.
The carbohydrates which are not sweet in
taste, amorphous in nature and generally
insoluble in water are called as non-sugars.
Eg. Starch, Cellulose, Glycogen etc.
Sugars and Non-sugars
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

12. All those sugars which reduce Tollen’s
reagent and Fehling’s solution are called
reducing sugars while others which do not
reduce these reagents are called non reducing
sugars.
Reducing and Non-reducing Sugars
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

13. Monosaccharides are of two types.

1.Aldoses: Monosaccharides containing
an aldehydic group (-CHO) are called
aldoses.

2. Ketoses: Monosaccharides containing a
keto group (>C=O) are called ketoses.

Classification of Monosaccharides
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

14. Aldose and ketoses are further classified
as trioses, tetroses, pentoses, hexoses etc.
according as they contain 3, 4, 5, 6 etc.
carbon atoms respectively.
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

15. The notations ‘D’ and ‘L’ are used to
describe the configurations of
monosaccharides.
Glyceraldehyde has been chosen as the
arbitrary standard for assigning the
configuration of monosaccharides.
Glyceraldehyde has an asymmetric carbon
and can exist as a pair of enantiomers as
follows.
‘D’ and ‘L’ Notations
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

16. In the Fischer projection, the
configuration of glyceraldehyde having the
–OH group attached to the bottom-most
asymmetric carbon on the right, is arbitrarily
assigned as ‘D’ and its mirror image having
the –OH group on the left, is arbitrarily
assigned the configuration ‘L’.
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

17. A monosaccharide is assigned the
configuration ‘D’ or ‘L’ depending upon
whether its configuration can be related to
D-Glyceraldehyde or L-Glyceraldehyde.
Almost all sugars found in nature have
‘D’ configuration.
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

18. A pair of diastereomers which differ in
configuration only about a single carbon
atom are called epimers.
For example, D-Glucose and D-Mannose
are C-2 epimers and D-Glucose and D-
Galactose are C-4 epimers.
Epimers
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

19. The change in specific rotation of aqueous
solution of an optically active compound to an
equilibrium value with time is known as
mutarotation.
The specific rotation of a freshly prepared
aqueous solution of α-D(+)-Glucose is +112°. If
this solution is allowed to stand, the specific
rotation decreases from +112° to a constant
value of +52.7° with time.
Mutarotation
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

20. Similarly, the specific rotation of a freshly
prepared aqueous solution of β-D(+)-Glucose
is +18.7°. If this solution is allowed to stand,
the specific rotation increases from +18.7° to
the same equilibrium value of +52.7° with
time.
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR

21. During mutarotation, the ring opens and
then again closes either in the original
position or in the inverted position giving an
equilibrium mixture of α-D(+)-Glucose and β-
D(+)-Glucose in solution and hence the same
equilibrium value of specific rotation is
attained.
CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR
 D(+)-Glucose D(+)-GlucoseOpen Chain Structure
(36 %) (64 %) (0.01%)

22. CHEMISTRY DEPARTMENT, MAHARANA PRATAP P. G. COLLEGE, JUNGLE DHUSAN, GORAKHPUR