Aromaticity (Huckel's Rule) 

Benzene and other aromatic compounds which resembles benzene in certain characteristic properties are called aromatic compounds.

These characteristic properties constitute one is commonly known as aromatic characteristics or Aromaticity.

1. An aromatic compound is cyclic & planer

2. π Electron cloud to be formed each P-Orbital must be label to overlap with P-Orbital on either side of a molecule must be planer.

3. The cyclic  π molecular orbital (electron cloud) formed by overlapping of P-Orbital must contain 4n+2π where n = 0,1,2,3,4,5. This phenomenon is known as Huckel's Rule according to the Huckel's Rule a number of π electrons in an aromatic compounds may be n = 0,1,2,3,4,5..............

Huckel's extended the application of his rule to known benzonide heterocyclic aromatic system also some modifications.

Example:-

In hetero atoms contribute a non bonded P-Orbital pairs of electrons present inside the ring which is counted towards deciding the aromaticity of these compounds.