Page 279 - Chemistry ICSE Class X

Organic Chemistry 265
CH – CH – CH – CH 3 CH – CH – CH 3
2
3
3
2
– Butane and 2-methylpropane are
CH 3 isomers͘ /Ŷ ŽƚŚĞƌ ǁŽƌĚƐ͕ n-butane
IUPAC name: butane 2-methylpropane and iso-butane are the two isomers
Common name: n-butane iso-butane of butane͘
Therefore, the compounds described by these two structural formulae ͻ
are the isomers of C H (butane). Isomerism is possible only in
4
10
hydrocarbons containing four or
What are the characteristics of isomers more carbon atoms͘ dŚƵƐ͕ ŵĞƚŚĂŶĞ͕
ĞƚŚĂŶĞ ĂŶĚ ƉƌŽƉĂŶĞ ĚŽ ŶŽƚ ƐŚŽǁ
ƒ Isomers have the same molecular formula ŝƐŽŵĞƌŝƐŵ͘
ƵƚĂŶĞ͕ ƉĞŶƚĂŶĞ͕ ŚĞdžĂŶĞ ĂŶĚ
ƒ Isomers have different structural formulae ŚĞƉƚĂŶĞ ;ĂŶĚ ƐŽ ŽŶͿ ƐŚŽǁ ŝƐŽŵĞƌŝƐŵ͘
ƒ Isomers have different physical and chemical properties. ͻ
dŚĞ ŝƐŽŵĞƌƐ ĐĂŶ ďĞ ŝĚĞŶƟĮĞĚ ĂŶĚ
Isomers show different properties due to the different arrangement of ĚŝƐƟŶŐƵŝƐŚĞĚ ĨƌŽŵ ŽŶĞ ĂŶŽƚŚĞƌ
carbon atoms in their molecules. ďĞĐĂƵƐĞ ŽĨ ĚŝīĞƌĞŶĐĞ ŝŶ ƚŚĞŝƌ
physical and ĐŚĞŵŝĐĂů ƉƌŽƉĞƌƟĞƐ͘
How many different types of isomerism occur
$TQCFN[ VJG KUQOGTKUO OC[ DG ENCUUKſGF KPVQ VYQ V[RGU viz.
ƒ Structural isomerism
ƒ Stereoisomerism
6JGUG VYQ V[RGU QH KUQOGTKUOU CTG HWTVJGT ENCUUKſGF KPVQ FKHHGTGPV
classes. At this stage, you will learn only about structural isomerism.

Structural Isomerism

The structural isomerism arises due to the difference in the arrangement
of atoms within the molecule, i.e., the structural isomers differ in their
structures.
6JGTG CTG ſXG FKHHGTGPV YC[U D[ YJKEJ VJG UVTWEVWTCN KUQOGTKUO KU GZJKDKVGF
These are described below.
What is the chain isomerism
The chain isomerism arises from the difference in the structure of the carbon
chain. For example.

Chain isomers of alkanes
ƒ Butane (C H ) exhibits the following two chain isomers:
4
10

The IUPAC names are given in bold
ůĞƩĞƌƐ͘