[Chemistry Class Notes] on Aromaticity Pdf for Exam

The word aroma is used to signify the fragrance or the smell of an object. It has been observed that most of the aromatic compounds are derivates of benzene and even benzene has an aroma of its own, so these classes of compounds have been denoted as Aromatic compounds. Aromaticity has been usually used to refer to molecules that have resonance in them. Like in the field of organic chemistry, the term Aromaticity is used to describe the property of a cyclic, planar molecule with a ring of resonance bonds that exhibits greater stability than other geometric or connective arrangements with the same set of atoms

Some of the examples of aromatic compounds are Benzene, Naphthalene, etc.

Rules of Aromaticity

For a compound to be aromatic, it must possess the following characteristics such as:

• The molecule must be cyclic, for example, Benzene.

• Each atom in the cyclic ring must be conjugated. As it will facilitate the dispersion of the cyclic ring delocalized pi-electron system. Hence, we can say that every atom in the cyclic ring must have an empty p orbital and must be capable of participating in resonance.

• All compounds that are aromatic must always obey Huckel’s Rule i.e. molecules must have 4n+24n+2 pi-electrons. Forex, Benzene has 6 pi-electrons and [(4×1)+2] = 6, thus it obeys Huckel’s Rule while cyclooctatetraene has 8 pi-electrons 4n+24n+2 ≠ 8, hence it does not follow Huckel’s Rule. So, benzene is aromatic while cyclooctatetraene is a non-aromatic compound. 

• The molecule must be planar or flat. Those compounds that follow the above rules of Aromaticity are generally flat as in that condition they possess extremely large potential energy.