Pyrazine

Pyrazine is an aromatic six-membered ring compound with formula C₄H₄N₂ and nitrogen atoms opposite each other. It is the simplest member of the pyrazine family of compounds.

Aromaticity: A chemical property of cyclic, conjugated molecules stabilized by delocalized electrons. Pyrazine’s six π electrons give its ring aromatic character.
Molecular orbital: A quantum-mechanical description of an electron state extending over one or more atoms in a molecule. Pyrazine’s delocalized π molecular orbitals account for its aromatic ring.
Pyrazine derivatives: Compounds containing a pyrazine ring modified by substituents or fused ring systems. Substitution expands the parent ring into compounds with varied chemical and biological properties.
Heterocyclic nomenclature: The system for naming cyclic compounds containing one or more noncarbon ring atoms. The name pyrazine identifies a specific arrangement of nitrogen atoms in a six-membered ring.
Heterocyclic compound: A cyclic compound whose ring contains at least one atom other than carbon. Pyrazine belongs to this broad structural class because its ring contains nitrogen.
Pyridine-like nitrogen: A ring nitrogen whose lone pair lies outside the aromatic π-electron system. Both pyrazine nitrogens have lone pairs available for protonation.
Pyrazinamide: An antimycobacterial drug used as part of combination treatment for tuberculosis. This pyrazine derivative is a clinically important medicine.
Tautomerism: The interconversion of structural isomers through the migration of an atom and a shift in bonding. The related dihydropyrazine chemistry illustrates how hydrogenation changes the ring’s bonding.
Pyridine: An aromatic six-membered ring compound with formula C₅H₅N and one ring nitrogen. Replacing one carbon in pyrazine’s ring with nitrogen gives pyridine’s ring pattern.
Basicity: The tendency of a chemical species to accept a proton or donate an electron pair. Pyrazine is a weak base because its ring nitrogens accept protons reluctantly.

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PyrazoleCompared with: Its larger ring and separated nitrogens contrast with pyrazole’s five-membered adjacent-nitrogen ring.