Is "benzene" an aromatic species? What about "cyclohexane", "cyclohexene", and "1.4-cyclohexadiene"?

1 Answer
Jul 9, 2016

An aromatic compound requires (4n+2)pi electrons constrained in a ring. Benzene, fulfills these criteria; C_6H_12, C_6H_10, C_6H_8 do not.

Explanation:

Benzene, C_6H_6, has 6 pi electrons, which are delocalized around a carbocycle. While a cyclohexatriene structure is often used to represent benzene, a hexagon enclosing a circle is probably a better representation of its aromaticity, and the non-locality of its pi electrons.

In neither the saturated nor the unsaturated carbocylic rings are the electrons delocalized, nor are any of these structures planar.

Chemists use the idea of aromaticity to rationalize the observed chemistry, and special stability of those compounds that they designate as "aromatic". It turns out that this simple idea of 6pi electrons is pretty powerful, and can be extended to rationalize the chemistry of heterocycles such as pyrrole, C_4H_4NH and furan C_4H_4O.