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Pyrimidine chemical structure.png
IUPAC name
Other names 1,3-Diazine, m-Diazine
CAS number 289-95-2 Yes check.svgY
PubChem 9260
MeSH pyrimidine
Molecular formula C4H4N2
Molar mass 80.088
Melting point

20–22 °C

Boiling point

123–124 °C

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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring.[1] It is isomeric with two other forms of diazine.



Three nucleobases found in nucleic acids, cytosine (C), thymine (T), and uracil (U), are pyrimidine derivatives:

Chemical structure of cytosine Chemical structure of thymine Chemical structure of uracil

In DNA and RNA, these bases form hydrogen bonds with their complementary purines. Thus the purines adenine (A) and guanine (G) pair up with the pyrimidines thymine (T) and cytosine (C), respectively.

In RNA, the complement of A is U instead of T and the pairs that form are adenine:uracil and guanine:cytosine.

These hydrogen bonding modes are for classical Watson-Crick base pairing. Other hydrogen bonding modes ("wobble pairings") are available in both DNA and RNA, although the additional 2'-hydroxyl group of RNA expands the configurations through which RNA can form hydrogen bonds.

Chemical properties

A pyrimidine has many properties in common with pyridine, as the number of nitrogen atoms in the ring increases the ring pi electrons become less energetic and electrophilic aromatic substitution gets more difficult while nucleophilic aromatic substitution gets easier. An example of the last reaction type is the displacement of the amino group in 2-aminopyrimidine by chlorine[2] and its reverse.[3] Reduction in resonance stabilization of pyrimidines may lead to addition and ring cleavage reactions rather than substitutions. One such manifestation is observed in the Dimroth rearrangement.

Compared to pyridine, N-alkylation and N-oxidation is more difficult, and pyrimidines are also less basic: The pKa value for protonated pyrimidine is 1.23 compared to 5.30 for pyridine.

Pyrimidine also is found in meteorites, although scientists still do not know its origin, Pyrimidine also photolyticly decomposes into Uracil under UV light.[4]

Organic synthesis

Pyrimidines can also be prepared within the laboratory by organic synthesis. One method is the classic Biginelli reaction. Many other methods rely on condensation of carbonyls with amines for instance the synthesis of 2-Thio-6-methyluracil from thiourea and ethyl acetoacetate [5] or the synthesis of 4-methylpyrimidine with 4,4-dimethoxy-2-butanone and formamide [6].

A novel method is by reaction of certain amides with carbonitriles under electrophilic activation of the amide with 2-chloro-pyridine and trifluoromethanesulfonic anhydride [7]:

Pyrimidine Synthesis Movassaghi 2006

See also


  1. ^ Heterocyclic Chemistry (3rd Edition) Thomas. L. Gilchrist ISBN 0-582-27843-0
  2. ^ Organic Syntheses, Coll. Vol. 4, p.182 (1963); Vol. 35, p.34 (1955) Link
  3. ^ Organic Syntheses, Coll. Vol. 4, p.336 (1963); Vol. 35, p.58 (1955) Link
  4. ^ Nuevo M, Milam SN, Sandford SA, Elsila JE, Dworkin JP (2009). "Formation of uracil from the ultraviolet photo-irradiation of pyrimidine in pure H2O ices.". Astrobiology 9 (7): 683-95. PMID 19778279.  
  5. ^ Organic Syntheses, Coll. Vol. 4, p.638 (1963); Vol. 35, p.80 (1955) Link
  6. ^ Organic Syntheses, Coll. Vol. 5, p.794 (1973); Vol. 43, p.77 (1963) Link
  7. ^ Single-Step Synthesis of Pyrimidine Derivatives Mohammad Movassaghi and Matthew D. Hill J. Am. Chem. Soc.; 2006; 128(44) pp 14254 - 14255; (Communication) doi:10.1021/ja066405m


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