Английская Википедия:Basic aromatic ring

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Basic aromatic ring systems
Файл:Pyridine structure.png
Pyridine
Файл:Quinoline structure.svg
Quinoline
Файл:Isoquinoline structure.png
Isoquinoline
Файл:Acridin.svg
Acridine
Файл:Pyrazine structure.png
Pyrazine
Файл:Quinoxaline structure.png
Quinoxaline
Файл:Imidazole structure.png
Imidazole
Файл:Benzimidazole structure.png
Benzimidazole
Файл:Purine structure.png
Purine
Файл:Pyrazole structure.png
Pyrazole
Файл:Indazole structure.png
Indazole
Файл:Pyrimidine structure.png
Pyrimidine
Файл:Quinazoline structure.png
Quinazoline
Файл:Pyridazine structure.png
Pyridazine
Файл:Cinnoline structure.png
Cinnoline

Basic aromatic rings are aromatic rings in which the lone pair of electrons of a ring-nitrogen atom is not part of the aromatic system and 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 of electrons of the nitrogen atom is delocalized and contributes to the aromatic pi electron system. In these compounds the nitrogen atom is connected to a hydrogen atom. 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.[1]

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

References

Шаблон:Reflist

See also