Azine (heterocycle)

Hantzsch–Widman nomenclature uses the name azines for a group of compounds related to benzene. They are aromatic rings where some carbon atoms have been replaced by nitrogen. Because the name "azine" is also used for a different group of chemicals, these chemicals are sometimes called azabenzenes.

 Types 
Azines are grouped by the number of nitrogen atoms.
 Azines with one nitrogen atom are called pyridines.
 Azines with two nitrogen atoms are called diazines. They are split up further by how close the nitrogen atoms are: if they are on opposite sides, it is called pyrazine. If they have one carbon atom between them, it is called pyrimidine. If they are next to each other, it is called pyridazine.
 Azines with three nitrogen atoms are called triazines.
 Azines with four nitrogen atoms are called tetrazines.
 Azines with five nitrogen atoms are called pentazines.
 Only one azine with six nitrogen atoms could exist, but has never been made. This hypothetical chemical compound would be an allotrope of nitrogen called hexazine.

 Sources 

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