In organic chemistry, diazines are a group of organic compounds having the molecular formula C4H4N2. Each contains a benzene ring in which two of the C-H fragments have been replaced by isolobal nitrogen. There are three structural isomers:
Pyrimidine (C4H4N2; /pɪˈrɪ.mɪˌdiːn, paɪˈrɪ.mɪˌdiːn/) is an aromatic, heterocyclic, organic compound similar to pyridine (C5H5N). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The other diazines are pyrazine (nitrogen atoms at the 1 and 4 positions) and pyridazine (nitrogen atoms at the 1 and 2 positions).
In nucleic acids, three types of nucleobases are pyrimidine derivatives: cytosine (C), thymine (T), and uracil (U).
Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula C4H4N2. It contains a six-membered ring with two adjacent nitrogen atoms. It is a colorless liquid with a boiling point of 208 °C. It is isomeric with two other diazine (C4H4N2) rings, pyrimidine and pyrazine.