NEET Chemistry Notes Some Basic Principles and Techniques – Isomerism
Isomerism
Isomerism
The compound having same molecular formula but differ in properties are known as isomers and the phenomenon is called isomerism.
Structural Isomerism
In this type of isomerism, compounds have same molecular formula but different structures.
- Chain Isomerism
It arises when two or more compounds have similar molecular formula but different carbon skeletons, e.g.
- Position Isomerism
It arises when two or more compounds have same molecular formula but different position of functional groups or substituents
- Functional Isomerism
It arises when two or more compounds have the same molecular formula but different functional group, e.g. C3H60 represents an aldehyde and a ketone as:
- Metamerism
It arises due to different alkyl groups on either side of the same functional group in the molecule
e.g.
- Tautomerism
It is a special type of functional isomerism arises in carbonyl compounds containing 
atom.
e.g.
Stereoisomerism
The compounds having same molecular formula but different spatial arrangement of atoms or groups are called stereoisomers and the phenomenon is called stereoisomerism.
Stereoisomerisnf is of three types:
- Geometrical Isomerism
The isomers having same molecular formula but different spatial arrangement of atoms about the double bond are known as geometrical isomers and this phenomenon is called geometrical isomerism, e.g.
- Optical Isomerism
Compounds having similar physical .and chemical properties but differ only in behaviour towards plane polarised light are called enantiomers and show optical isomerism
- Conformational Isomerism
In conformational isomerism because of the free rotation of carbon-carbon single bond, different arrangement of atoms in space are obtained.
Fission of a Covalent Bond
Carbon forms a number of different types of organic compounds because it forms covalent bonds with itself and with other elements like Ii, O, N, X, P and S etc., in a variety of ways. For better understanding of organic chemistry, it is necessary to understand some basic terms, processes and basic principles. The organic reactions begin with the breakage of covalent bond.
Homolytic Fission
In this, one of the electrons of the shared pair in a covalent bond goes with each of the bonded atoms. Generally, homolytic fission takes place in non-polar covalent molecules in the presence of sunlight or high temperature.
Heterolytic Fission
In this, the bond breaks in such a fashion that the shared pair of electrons goes with one of the fragments, arising positive and negative charges.
Heterolytic fission generally takes place in polar covalent molecules but in non-polar molecules, it takes place in the presence of catalyst like AlC13 (anhyd.), FeC13 (anhyd.) etc.
Reaction Intermediates
Most of the chemical reactions require certain chemical species to occur. These species are generally short lived, highly reactive and are called reactive intermediates, e.g. free radicals, carbocations, carbanions, carbenes, nitrenes, etc.