Aromatic
In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. (More properly, these bonds may be seen as a hybrid of a single bond and a double bond, each bond in the ring being identical to every other.) This commonly seen model of aromatic rings was developed by Friedrich August Kekulé von Stradonitz. The model for benzene consists of two resonant forms, which corresponds to the double and single bonds switching positions. Another representation is that of the circular pi bond, in which the electron density is evenly distributed through a pi bond above and below the ring. This model more correctly represents the location of electron density within the aromatic ring.Molecules which are not aromatic are said to be aliphatic.
Aromaticity was discovered by Kekulé in benzene, and was first explained in quantum mechanical terms by Linus Pauling in the 1930s.