Pyrimidine - Wikipedia
https://en.wikipedia.org/wiki/PyrimidinePyrimidine is an aromatic heterocyclic organic compound similar to pyridine. One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has the 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).
pyrimidine - Wiktionary
https://en.wiktionary.org/wiki/pyrimidinepyrimidine. Wikipedia. Structural formula of pyrimidine. pyrimidine ( plural pyrimidines ) ( organic chemistry) A diazine in which the two nitrogen atoms are in the meta- positions; it is the basis of three of the bases found in DNA and RNA: thymine, uracil and cytosine.