Aromaticity#Heterocyclics

With a heteroaromatic is an aromatic, the ring structure contains one or more heteroatoms. An example is pyridine, because it is, in principle, dealing with a benzene ring, except that a CH group has been replaced by a nitrogen atom.

Properties

The heteroaromatic compounds are characterized by a benzene analog - Elektronensextet (see Hückel rule). They are divided into electron - rich and electron-deficient heteroaromatics. Since the 5- rings have a higher electron density than the 6- rings, include the 5 -rings just to the - electron-rich heteroaromatics.

The electron -rich heteroaromatics are expected to be more reactive than the aromatics without heteroatom. However, the reactivity decreases with increasing group number and period of the heteroatom. So, for example, tends Pyrrole for autopolymerization while furan forms under the action of air quickly brown oxides, which can be thermally split again. Thiophene, however, is in the air already quite stable. Additional heteroatoms affect the stability as a function of their position in the ring. For example, a nitrogen atom in the 3-position in general to a chemical stabilization of a - electron-rich heteroaromatic (see sized canvases. Imidazole, oxazole, thiazole )

Typical representatives

Designations according to Hantzsch Widman system:

Bi-and polycyclic systems

Bicyclic heteroaromatic compounds are, for example, benzofuran, purine, or indole.

Many alkaloids, such as nicotine containing heteroaromatic structure elements.