Aromaticity

Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. It can also be considered a manifestation of cyclic delocalization and of resonance. An aromatic compound is one which has a ring structure around which electrons may move. That is, the electrons are not tied to a single atom or pair of atoms, they are shared by all the atoms around the ring. For this to be the case, certain conditions must be met:

• the ring must be planar (or nearly planar), each atom in the ring must have a p-orbital perpendicular to the plane of the ring. These overlapping p-orbitals generate an array of pi-orbitals, and

• the pi-orbitals must contain at least 4n+2 electrons, where n=0,1,2... This requirement is known as The Hückel Rule.

The electrons that travel around the ring are said to be delocalized.

Examples of aromatic compounds include: benzene, pyridine, furan, pyrrole.

CATEGORIES: Nanoscience