Basic aromatic ring

Basic aromatic ring systems
File:Pyridine structure.png Pyridine	File:Quinoline structure.png Quinoline	File:Acridin.svg Acridine
File:Pyrazine structure.png Pyrazine	File:Quinoxaline structure.png Quinoxaline	File:Phenazine.png Phenazine
File:Imidazol (vzorec).svg Imidazole	File:Benzimidazole structure.png Benzimidazole	File:Purine structure.png Purine
File:Pyrimidine structure.png Pyrimidine	File:Quinazoline structure.png Quinazoline	File:Pteridin - Pteridine.svg Pteridine
File:Pyrazole structure.png Pyrazole	File:Indazol.svg Indazole
File:Pyridazin.svg Pyridazine	File:Cinnoline structure.png Cinnoline

Basic aromatic rings are heterocyclic aromatic compounds in which the lone pair of electrons of a ring-nitrogen atom is not part of the aromatic system, but instead extends in the plane of the ring. This lone pair is responsible for the basicity of these nitrogenous bases, similar to the nitrogen atom in amines. In these compounds the nitrogen atom is not connected to a hydrogen atom. Basic aromatic compounds get protonated and form aromatic cations (e.g. pyridinium) under acidic conditions. Typical examples of basic aromatic rings are pyridine or quinoline. Several rings contain basic as well as non-basic nitrogen atoms, e.g. imidazole and purine.

In non-basic aromatic rings, the lone-pair electrons of the nitrogen atom is delocalized and contributes to the aromatic pi electron system and is therefore not available to react with acids or other electrophilic atoms. Examples of non-basic nitrogen-containing aromatic rings are pyrrole and indole. Pyrrole contains a lone pair that is part of the pi-conjugated system, so it is not available to deprotonate an acidic proton.

The basic aromatic rings purines and pyrimidines are nucleobases found in DNA and RNA.

See also

• Simple aromatic ring