Cytosine

Cytosine
Names
	Preferred IUPAC name 4-Aminopyrimidin-2(1H)-one
	Other names 4-Amino-1H-pyrimidine-2-one
Identifiers
CAS Number	71-30-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:16040 ;
ChEMBL	ChEMBL15913 ;
ChemSpider	577 ;
ECHA InfoCard	100.000.681
KEGG	C00380 ;
MeSH	Cytosine
PubChem CID	597;
UNII	8J337D1HZY ;
CompTox Dashboard (EPA)	DTXSID4044456 ;
	InChI InChI=1S/C4H5N3O/c5-3-1-2-6-4(8)7-3/h1-2H,(H3,5,6,7,8) Key: OPTASPLRGRRNAP-UHFFFAOYSA-N ; InChI=1/C4H5N3O/c5-3-1-2-6-4(8)7-3/h1-2H,(H3,5,6,7,8) Key: OPTASPLRGRRNAP-UHFFFAOYAY;
	SMILES O=C1Nccc(N)n1;
Properties
Chemical formula	C4H5N3O
Molar mass	111.10 g/mol
Density	1.55 g/cm3 (calculated)
Melting point	320 to 325 °C (608 to 617 °F; 593 to 598 K) (decomposes)
Acidity (pKa)	4.45 (secondary), 12.2 (primary)
Magnetic susceptibility (χ)	−55.8·10−6 cm3/mol
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Cytosine (/ˈsaɪtəˌsiːn, -ˌziːn, -ˌsɪn/) (symbol C or Cyt) is one of the four nucleotide bases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at position 2). The nucleoside of cytosine is cytidine. In Watson–Crick base pairing, it forms three hydrogen bonds with guanine.