CSIR-NET Chemical Science: Short Notes on Aromaticity!

By Renuka Miglani|Updated : June 24th, 2021

Hi Students,

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Are you looking for some short and reliable notes during your CSIR-NET preparations? Then, you have come to a perfect place!

Candidates who are preparing for their CSIR NET exam might in need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point of time, We at BYJU'S Exam Prep come up with short notes on the Aromaticity which comes under the Organic Chemistry section of the Chemical Science syllabus

This set of short notes on Aromaticity has been meticulously designed by our experienced subject-matter experts to give you the most standard set of study materials to be focused upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them in the learning process and for their future. Here we are offering the best study notes that are reliable and can be used by the students during their preparations for the upcoming CSIR-NET 2021 exam.


Aromaticity can be defined as a property of conjugated cycloalkenes which helps in enhancing the stabilization of the molecule .This happens because of the delocalization of π electrons. 

The Hückel's rule for aromaticity are:

  1.   Molecule is cyclic
  2.   Every atom of the ring must have one p orbital
  3.   The molecule should be planar and every atom must have an sp2 hybridized orbital
  4.   The molecule must have 4n+2 pi-bond electrons, where n is equal to any integer (0,1,2,3,…)

According to Hückel's Molecular Orbital Theory, a compound is stable if all the bonding molecular orbitals are completely filled with a pair of electrons. No anti-bonding orbital should be occupied.

Benzene has 6 π electrons. The first 2 π electrons fill up the lowest energy orbital, and the remaining 4 π electrons get filled in the succeeding energy level. In this manner ,all its bonding orbitals are filled, but none of the anti-bonding orbitals have any electrons. Therefore, the molecule shows exceptional stability


Aromatic compounds are highly stable compounds. On the other hand, Anti-aromatic compounds have an unusual instability. They have similar rules to aromaticity except the fact that the molecule has a closed loop of 4n pi-bond electrons.


Benzenoid and Non-benzenoid compounds

Benzenoid compounds:

These molecules contain at least one benzene ring in their structure. A benzene ring has a cyclic structure and has six carbon atoms. It has a conjugated pi system containing alternate double and single bonds.

Since the molecule has double bonds because of the presence of a benzene ring, the molecule shows extra stability provided by the conjugated pi system. For example toluene


Non-benzenoid compounds:

These molecules exhibit an aromatic behaviour without having any benzene nucleus . They have one or more rings fused but none of the rings is a benzene ring . The ring structure of these compounds might contain 5-7 etc number of carbons. The most common example is AZULENE . It is a system of two fused rings , one containing 7 and the other 5 carbons.


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