CHEMISTRY TEXTBOOK

Fig. 14.6 : Haworth formula of anomers of

glucopyranose

O

HO

OH

OH

OH

α- side

(α- D - (+) - Glu-

copyranose)

CH 2 OH

H

H H H

H

6

5

4

3 2

1

O

HO

OH

OH

OH

β - side

(β - D - (+) -

Glucopyranose)

CH 2 OH

H

H

H H

H

6

5

4

3 2

1

O

(Pyran)

its anomeric hydroxyl (-OH) group (at C-1)
on the β-side. The groups which appear on
right side in the Fischer projection formula
appear on α-side in the Haworth formula, and
viceversa.
14.2.7 Reducing nature of glucose :
Hemiacetal group of glucopyranose structure
is a potential aldehyde group. It imparts
reducing properties to glucose. Thus, glucose
gives positive Tollens test and positive
Fehling test (Section 12.8.1 a).

14.2.8 Representation of Fructose structure

Fructose (C 6 H 12 O 6 ) is a laevorotatory

ketohexose. Fructose is also called laevulose

due to its laevorotation [∝]

20

D = -92.4^0. Being

an ∝-hydroxy keto compound fructose is

a reducing sugar. In free state it exists

as mixture of fructopyranose (major) and

fructofuranose. In combined state fructose

is found in the form of fructofuranose ring

structre (as in sucrose, see section 14.2.9). The

name furanose is given by analogy with furan,

a five membered heterocyclic compound.

Figure 14.7 shows representations of open

chain structure of fructose and ring structures

of ∝- and β- anomers of fructofuranose. Ring

structure of fructose is a hemiketal (section

12.8.2 c).

14.2.9 Disaccharides : Disaccharides

give rise to two units of same or different

monosaccharides on hydrolysis with

dilute acids or specific enzymes. The two

monosaccharide units are linked together by an

ether oxide linkage (-O-), which is termed as

glycosidic linkage in carbohydrate chemistry.

Glycosidic linkage is formed by removal of a

water molecule by reaction of two hydroxyl

1

2

O

Furan

HO

C = O

OH

OH

CH 2 OH

CH 2 OH

H

H

H

Open chain structure of fructose

HO

HOH 2 C OH

OH

O

CH 2 OH

H

H

H

1 2 3 4 5 6

∝-D-(-) - Fructofuranose

HO

HO CH 2 OH

OH

O

CH 2 OH

H

H

H

2 1

3

4

5

6

β -D-(-) - Fructofuranose

O

HO

HO OH

α- side

α- D - (-) - Fructofuranose

HO- H 2 C CH 2 - OH

H H

H

6

5

(^43)
1
2
Fig. 14.7 : Representations of fructose structure
3
4
5
6
O
OH
HO
OH
α- side
β - D - (-) - Fructofuranose
HO- H 2 C
H H C H 2 - OH
H
6
5
4 3 1
2
β- side β- side