Engineering Chemistry S Datta

160 ENGINEERING CHEMISTRY
Isomerism
Different organic compounds having the same molecular formula are known as isomers.
The phenomenon is known as isomerism.
The isomerism is of two types:
(i) Structural isomerism
(ii) Stereoisomerism.
Structural isomerism may be classified as:
(a) Chain isomerism
(b) Functional group isomerism
(c) Position isomerism
(d) Metamerism.
Examples are displayed in the following table.
Types of isomerism Molecular formula Different structures (Compounds)
(a) Chain isomerism (i) Butane [C 4
H 10
] (i) CH 3—CH 2—CH2⎯CH3
n-butane
(ii) CH3⎯CH ⎯CH3
⏐
CH3
Isobutane
(ii) Pentane [C 5
H 12
] (i) CH 3
—CH 2
—CH 2
—CH 3
n-pentane
CH3
⏐
(ii) CH 3
— CH—CH 2
—CH 3
Isopentane
CH3
⏐
(iii) CH3
⎯C⎯CH
⏐
CH3
Neopentane
3
(b) Functional group (i) C 2
H 6
O (i) CH 3
CH 2
OH (ii) CH 3
—O—CH 3
isomerism ethyl alcohol dimethyl ether
(ii) C 3
H 6
O
(i) CH .CH .CHO
3 2
Propanaldehyde
(ii) CH COCH 3 3
acetone
(c) Position isomerism (i) C 3
H 8
O (i) CH CH CH OH
3 2 2
n-propylalcohol
(ii) CH 3
—CH —CH 3
⏐
OH
isopropylalcohol
(ii) C 3
H 7
Cl
(i) CH .CH .CH .Cl
3 2 2
1-chloropropane
(ii) CH 3
—CH —CH 3
⏐
Cl
2-chloropropane
(Contd.)