CSIR-NET Chemical Science: Short Notes on Aromaticity!

Aromaticity

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.

Short Notes on Aromaticity - Download Now

Hope the above article was helpful for you. Keep Upvote this article and share it among your friends!

Check Out: 

• Study Notes for CSIR NET Life Science - BIOCHEMISTRY (Download PDF)
   
• Study Notes for CSIR NET Chemical Science - Download PDF Here!
   

→ If you have any questions feel free to ask in the comments section below.

Best of Luck!!
Sahi Prep hai to Life Set Hai!!
Go BYJU'S Exam Prep