Azine

Azine is a term used in organic chemistry to describe a class of nitrogen-containing heterocyclic compounds that typically feature a six-membered aromatic ring with two nitrogen atoms in the ring. The best-known members are the diazines, among which pyrazine, pyridazine, and pyrimidine are the most frequently encountered. These compounds differ in the relative positions of the two nitrogens.

Pyrazine has nitrogen atoms at the 1 and 4 positions, pyridazine at 1 and 2, and pyrimidine at 1 and 3. Collectively, they are called diazines and are distinguished from other azines by the specific arrangement of nitrogen atoms. The ring remains aromatic, and the presence of two ring nitrogens makes the azine ring less basic than benzene or pyridine.

Azines are of considerable importance in biology and medicine. Pyrimidines form the core of the nucleobases cytosine, thymine, and uracil in DNA and RNA. Pyrazines and related compounds are used as reagents, intermediates in pharmaceuticals, and components of dyes and agrochemicals. Coordination chemistry also exploits azines as ligands.

Approaches to synthesis include cyclization and condensation reactions that assemble the six-membered ring from suitable precursors, as well as annulation of nitrogen-containing fragments. The term azine also serves as a generic naming suffix for nitrogen-containing heterocycles with two nitrogens, with higher-nitrogen analogues such as triazines carrying three nitrogens. In naming, specific diazines are often given by the positions of the nitrogens in the ring.