1. Isomers and Isomerism
• In organic chemistry, we come across some
compounds which have similar number of
atoms but differ in physical and chemical
properties and are called isomers and the
phenomenon is called isomerism
• Isomers have same molecular formula but
differ in arrangement of atoms within a
molecule

2. Types of isomerism
• Mainly isomerism is of two types
– 1. Structural isomerism
– 2. Stereoisomerism
1-Structural isomers
– Are compounds having same molecular formula but
different structural formula

3. –These are of further 5 types
• Chain isomerism
• Position isomerism
• Functional isomerism
• Metamerism
• Tautomersim

4. • Stereoisomers
– Are compounds having same structural
formula but different in arrangement
of atoms in space
– Stereoisomers are of two types
• Geometrical or Cis-Trans isomerism
• Optical isomerism

5. Structural isomerism
• Chain Isomerism
– Such compounds have the same molecular
formula but differ in the order in which the carbon
atoms are bonded to each other
– Examples are
• n-butane and isobutane

6. 2-methylbutane and 2, 2-dimethylpropane
Positional isomers
• Positional isomers have same molecular
formula but differ in the position of a
functional group on the carbon chain. For
example

7. •1-bromobutane and 2-bromobutane

8. Functional isomerism
• Functional isomers have same molecular
formula but differ in functional groups. For
example
– Ethyl alcohol and Dimethyl ether

9. Metamerism
• This type of isomerism is due to unequal
distribution of carbon atoms on either side of
the functional group
• Such compounds are members of homologous
series
• Example: Diethyl ether and Methyl propyl
ether

10. Tautomerism
• This is a special type of functional isomerism
in which isomers are in dynamic equilibrium
with each other
• For example: ethyl acetoacetate is an
equilibrium mixture of 2 forms-93% keto form
and 6% enol form

11. Geometric isomerism
• In alkenes two carbons are linked through
sigma bond (SP2 hybridized orbitals) and a pi
bond due to overlap of p orbitals
• In such compounds these two carbons along
with other 4 substituent remain in plane and
are locked
• Because rotation will break the double bond

12. • This restriction of rotation is responsible for
geometric isomerism in alkenes

13. • Consider the case of 2 butene. It exists in two
special arrangements
• Cis 2 butene and Trans 2 butene
• Such compounds are referred as geometrical
isomers

14. • Cis isomer is one in which two similar groups
are on the same side of a double bond
• Trans isomer is that in which two similar
groups are on the opposite side of the double
bond
• Conversion of such isomers into each other is
only possible if heated at high temperature or
absorb light. Energy around 62 Kcal/mole is
needed to break pi bond

15. • Trans isomers are more stable than the
corresponding cis isomer
• This is because in trans bulky groups are on
the opposite side, hence less repulsion or
steric hindrance
• Geometrical isomers have different physical
and chemical properties. These can be
separated by conventional techniques like
distillation and gas chromatography etc.

16. Geometrical isomerism in cyclic
compounds
• Geometrical isomerism is possible in cyclic
compounds
• There should be restriction of rotation if two
carbons are linked with a cyclic structure