Please scroll down to get to the study materials.
Compounds having same molecular formula but different physical and chemical properties due to different structures are known as isomers and the property itself is known as isomerism.
(Greek, Isos= equal, meros= parts)
For example -
Ethanol - C2H5OH, molecular formula - C2H6O
Methoxymethane - CH3-O-CH3, molecular formula - C2H6O
There are two types of isomerism:
1) Structural isomerism
Such type of isomers is due to different structures. It means isomers having same molecular formula but different structures are known as structural isomerism. For example -
Butane (C4H10) - CH3-CH2-CH2-CH3
2-Methyl propane (C4H10) -
Types of structural isomerism-
I) Pentane (C5H12) - It has three possible isomers. They are-
II) Hexane (C6H14) - It has 5 possible isomers. They are-
(I) Possible isomers of molecular formula C2H6O are - C2H5OH (Ethanol) and CH3-O-CH3 (methoxymethane).
Functional group is -OH (Alcohol)
(II) Possible isomers of molecular formulaC2H4O2 are - CH3COOH ( ethanoic acid) and HCOOCH3 (methyl methanoate).
The functional group is -COOH (carboxylic acid) and -COOR (ester group).
(III) Possible isomers of molecular formula C3H6O are- CH3-CO-CH3(propanone) and CH3-CH2-CHO (propanal),
(IV) Possible isomers of molecular formula C3H8O are- CH3-CH2-CH2-OH (propanol) and CH3-O-CH2CH3 (methoxy ethane).
i) C2H5-O-C2H5 (Ethoxyethane) , CH3-O-C3H7(Methoxypropane)
ii) C2H5-CO-C2H5 (3- pentanone) , CH3-CO-C3H7 (2- pentanone).
(i) Ethyl acetoacetate exists in two forms called keto and enol forms.
2) Stereo- isomers
When isomerism is caused by the different arrangements of atoms or groups in three-dimensional space, the phenomenon is called stereoisomerism.
The stereoisomers have the same structural formula but differ in the arrangement of atoms or group of atoms in a three-dimensional configuration.
It is of two types-
a) Geometrical or cis-trans isomerism
b) Optical isomerism
Adhikari, Rameshwar; Khanal, Santosh; Subba , Bimala; Adhikari, Santosh; Khatiwada, Shankar Pd. Universal Chemistry XI. First. Vol. 1st. Kathmandu: Oasis Publication, 2069.
Chaudhary, Ganga Ram; Karna, Shila Kant Lal; Sharma, Kanchan; Singh, Sanjay; Gupta, Dipak Kumar. A Textbook of Higher Secondary Chemistry XI. Ed. 2nd. Kathmandu: Vidyarthi Pustak Bhandar, 2069 (2012).