I-Pyrimidine iyinhlanganisela ephilayo ye-heterocyclic efana ne-pyridine. Enye yezinhlamvu ezintathu (i-heterocyclics ezinama-six nge-athomu amabili e-nitrogen ngaphakathi kwendandatho), ine-athomu ye-nitrogen ezikhundleni ze-1 ne-3 kule ring.:250 Amanye ama-pyrazine (ama-atrojeni e-1 nase-4) kanye ne-pyridazine (i-athomu ye-nitrogen e-1 nase-2 isikhundla). E-nucleic acids, izinhlobo ezintathu ze-nucleobases yiziqu ezivela ku-pyrimidine: i-cytosine (C), i-thymine (T), ne-uracil (U).