50.ORGANIC CHEMISTRY- Classification.

It gives me immense gratification to be writing this 50th post exactly after one year , since I started writing this blog.It gives me even more pleasure to be writing about a subject, in which I completed my Masters degree – Organic Chemistry! So, lets continue our discussion on organic compounds in this post.

Before we start classifying organic compounds,  it is imperative that we know the basic valency of some elements, when they form covalent bonds in organic compounds.This information is germane to our discussion as, it will help us in drawing correct molecular structures.

Always remember –
In any organic compound – 

A carbon atom always forms 4 bonds.
A nitrogen atom always forms 3 bonds.
An oxygen atom forms 2 bonds.
Halogens,Hydrogen form a single bond.


no.of bonds it forms











Classification of Organic Compounds –

A] Based on structure

The structure of organic compounds helps us classify them into different categories as shown in the figure below-


I]Open Chain/Aliphatic /Acyclic Compounds – Carbon atoms are linked to each other to form chains. Chains could be straight or branched. The word aliphatic has Greek origin, ‘aleiphar’ in greek  means ‘fat/oil’. Thus, this name refers to compounds that are not soluble in water and have a open chain of carbon atoms.


Saturated compounds have all single bonds in their structure. As shown in the figure below, they can have a straight chain or can have branching ,which gives rise to a wide variety of compounds.Among hydrocarbons, alkanes are saturated.


Unsaturated compounds have a double / triple bond in their structure.


Homocyclic  compounds have a closed ring structure and single bonds in them.They only have carbon and hydrogen atoms in them. They are NOT aromatic.


Homocyclic aromatic  (homo= of the same kind, cyclic = ring structure) compounds have only carbon and hydrogen in their structure.They have alternate double bonds.However, these alternating double bonds impart great stability to the structure and thus aromatic compounds are very different from the aliphatic unsaturated compounds.We shall study aromatic chemistry in great detail in our upcoming posts.


Alicyclic Heterocyclic compounds have single bonds in a closed ring structure of carbon atoms.However, a heteroatom ( atom apart from carbon and hydrogen e.g.- Nitrogen, oxygen, sulphur etc) is present in their structure.


Heterocyclic aromatic compounds have the aromatic ring structure and also have a heteroatom.



B]Based on functional groups

Organic compounds exhibit peculiar behaviour based on the functional group they have. Thus, they can also be classified according to these functional groups.

What is a functional group ?

It is a set of atoms which are responsible for  characteristic reactions of a particular compound.Addition of a functional group changes properties of a compound.The study of organic reactions is very intricately linked to the functional groups present in the molecule.

e.g. –  Consider methane CH4.It is an alkane. If one of the -H atom is replaced by -COOH functional group, it becomes acetic acid (CH3-COOH) , which has totally different properties than methane! 

So lets get to know some important functional groups in organic molecules.


Compounds containing same functional group belong to same class of organic compounds and their chemistry is very similar.

In our next post we shall continue our discourse on organic chemistry.Till then ,

Be a perpetual student of life and keep learning..

Good Day !


References and general reading –

3.Precise Chemistry textbook by Sheth Prakash Kendra.



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