COMPLETE ISOMERISM (THEORY + SOLVED EXAMPLES)

ISOMERISM
The name was given by Berzilius. Two or more than two organic compounds having the same molecular
formula and molecular weight but different physical and chemical properties are called isomers and the
phenomenon is called isomerism.

ISOMERISM

Structural Isomerism Stereoisomerism


Chain Position Ring Chain Functional Metamerism Tautomerism

 Structural Isomerism :

S .N o . Is o m er s C h a r a c t er is t ic s C o n d it io n s

They have different size of They have same nature of
1 Chain Isomers
main chain or side chain locant
They should have same size of
They have different position
2 Positional Isomers main chain and side chain and
of locant
same nature of locant

Chain and positional
3 Functional Isomers Different nature of locant
isomerism is not considered


Different nature of alkyl They should have same nature
4 Metamerism group along a polyvalent of functional group chain &
functional group positional isomer is ignored


The two functional isomers
Different position of hydrogen
5 Tautomerism remains in dynamics
atoms
equilibrium with each other


1. Chain Isomerism (CI) :
The compounds which have same molecular formula, same functional group, same position of functional
group or multiple bond or substituent but different arrangement of carbon chain (different parent name of
compound) shows chain isomerism.

Example : CH3 CH2 CH2 CH3 CH3 CH CH3

Butane(4C) CH3
2-Methyl propane (3C)


Example : CH3 CH2 CH CH2 CH2 C CH3
CH3
1–Butene(4C)
2-Methyl-1-propene(3C)

Example : CH3 CH2 CH2 CH2 OH CH3 CH CH2 OH

1-Butanol (4C) CH3
2-Methyl-1-propanol (3C)

, O O

Example : CH3 CH2 CH2 CH2 C OH CH3 CH CH2 C OH

CH3
Pentanoic acid
3-Methyl butanoic acid

CH3 O

CH3 C C OH

CH3

2,2-Dimethyl propanoic acid

2. Position Isomerism (PI) :
The compounds which have same molecular formula, same functional group, same parent carbon chain but
different position of functional group or multiple bond or substituents, shows position isomerism.
Example : CH2 CH CH2 CH3 CH3 CH CH CH3
But–1–ene But–2–ene

Example : CH3 CH2 CH2 CH2 OH CH3 CH2 CH CH3
OH
1–Butanol 2–Butanol
Example : CH3 CH2 CH2 CH2 Cl CH3 CH2 CH CH3
Cl
1–Chlorobutane 2–Chlorobutane
 Example of CI and PI :
(i) C 4 H 10 have two isomers : Both butane and isobutane are chain isomers.
Example : CH3 CH2 CH2 CH3 CH3 CH CH3
CH3
Butane Isobutane

(ii) C 5 H 12 have three isomers : All of three structures are chain isomers because only carbon chain (parent)
is different.
Example :

CH3

CH3 CH2 CH2 CH2 CH3 , CH3 CH2 CH CH3 , CH3 C CH3

CH3 CH3
Pentane 2–Methyl butane 2,2–Dimethylpropane

(iii) C 6 H 14 has 5 i somers :
(a) CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 (b) CH3 CH2 CH2 CH CH3
CH3
Hexane 2–Methyl pentane
(c) CH3 CH2 CH CH2 CH3 (d) CH3 CH CH CH3

CH3 CH3 CH3
3–Methyl pentane 2,3–Dimethyl butane

, CH3
(e) H3C C CH2 CH3  a–b, b–d, a–c, c–d  Chain Isomers

CH3
2,2–Dimethyl butane  b–c, d–e       Position Isomers
(iv) C 7 H 16 has 9 isomers

1. CH3 CH2 CH2 CH2 CH2 CH2 CH3 Heptane
2. CH3 CH2 CH2 CH2 CH CH3 2–Methylhexane
CH3
3. CH3 CH2 CH2 CH CH2 CH3 3–Methylhexane
CH3
CH3

4. CH3 CH2 CH2 C CH3 2,2–Dimethyl pentane
CH3
CH3

5. CH3 CH2 C CH2 CH3 3,3-Dimethylpentane
CH3
CH3

6. CH3 CH CH CH2 CH3 2,3–Dimethylpentane
CH3
CH3 CH3

7. CH3 CH CH2 CH CH3 2,4–Dimethylpentane
CH2 CH3

8. CH3 CH2 CH CH2 CH3 3–Ethylpentane
CH3
9. CH3 CH C CH3 2,2,3–Trimethylbutane
CH3 CH3
(v) C 3 H 6 Cl 2 has 4 isomers : Position of chlorine atom is different in all the structure, so these are position
Isomers.

Cl Cl

1. H3C CH2 CH Cl 2. H2C CH2 CH2 Cl

1,1–Dichloropropane 1,3–Dichloropropane

Cl Cl
3. H3C C CH3 4. H2C CH CH3
Cl Cl
2,2–Dichloropropane 1,2–Dichloropropane

(vi) C 5 H 11 Cl has 8 isomers