The necessary conditions for a molecule to be aromatic are:
(i)It should have a single cyclic cloud of delocalised pi electrons above and below the plane of the molecule.
(ii)It should be planar. This is because complete delocalisation of pi electrons is possible only if the ring is planar to allow cyclic overlap of p-orbitals.
(iii)It should contain Huckel number of electrons, i.e. (4n+2) pi electrons where n=0,1,2,3….etc.
A molecule which does not satisfy any one or more of the above condition is said to be non aromatic
