View source for Pyran

{{Chembox
| ImageFileL1=2H-Pyran.svg
| ImageSizeL1=75px
| ImageCaptionL1=2''H''-pyran
| ImageFileR1=4H-Pyran.svg
| ImageSizeR1=75px
| ImageCaptionR1=4''H''-pyran
| ImageFileL2=Pyran3d.png
| ImageSizeL2=75px
| ImageFileR2=4HPyran3d.png
| ImageSizeR2=75px
| IUPACName=2''H''-Pyran, 4''H''-Pyran
| OtherNames=2''H''-Oxine, 4''H''-Oxine
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo=289-66-7
| CASNo_Comment=(2''H'')
| CASNo1_Ref = {{cascite|correct|CAS}}
| CASNo1=289-65-6
| CASNo1_Comment=(4''H'')
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = CH5P2A5WTT
| PubChem=186148
| PubChem_Comment =(2''H'')
| PubChem1=136135
| PubChem1_Comment =(4''H'')
| SMILES =C1=CC=CCO1
| SMILES_Comment = (2''H'')
| SMILES1 = C1=CCC=CO1
| SMILES1_Comment = (4''H'')
| InChI = 1S/C5H6O/c1-2-4-6-5-3-1/h1-4H,5H2
| InChI_Comment = (2''H'')
| InChIKey = MGADZUXDNSDTHW-UHFFFAOYSA-N
| InChI1 = 1S/C5H6O/c1-2-4-6-5-3-1/h2-5H,1H2
| InChI1_Comment = (4''H'')
| InChIKey1 = MRUWJENAYHTDQG-UHFFFAOYSA-N
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 161812
| ChemSpiderID_Comment = (2''H'')
| ChemSpiderID1_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID1 = 119912
| ChemSpiderID1_Comment = (4''H'')
  }}
|Section2={{Chembox Properties
| C=5 | H=6 | O=1
| Appearance=
| Density=
| MeltingPt=
| BoilingPt=
| Solubility=
| pKa = 
| pKb = 
  }}
|Section3={{Chembox Hazards
| MainHazards=
| FlashPt=
| AutoignitionPt =
  }}
|Section8={{Chembox Related
| OtherCompounds = [[Dihydropyran]]<br>[[Tetrahydropyran]]
  }}
}}
In [[chemistry]], '''pyran''' is a six-membered [[heterocyclic]], non-[[Aromaticity|aromatic]] ring, consisting of five [[carbon]] atoms and one [[oxygen]] atom and containing two [[double bond]]s. The [[molecular formula]] is C<sub>5</sub>H<sub>6</sub>O. There are two [[isomer]]s of pyran that differ by the location of the double bonds. In '''2''H''-pyran''', the saturated carbon is at position 2, whereas, in '''4''H''-pyran''', the saturated carbon is at position 4. "Oxine” is not used for pyran because it has been used as a trivial name for quinolin-8-ol.<ref>{{Cite web |title=Blue Book chapter P-2 |url=https://iupac.qmul.ac.uk/BlueBook/P2.html |access-date=2025-02-05 |website=iupac.qmul.ac.uk}}</ref>

4''H''-Pyran was first isolated and characterized in 1962 via [[pyrolysis]] of 2-acetoxy-3,4-dihydro-2''H''-pyran.<ref>{{cite journal|title=γ-Pyran|author1=Masamune, S.|author2=Castellucci, N. T.|journal=Journal of the American Chemical Society|year = 1962|volume=84|issue=12|pages=2452–2453|doi = 10.1021/ja00871a037}}</ref> It was found to be unstable, particularly in the presence of air. 4''H''-pyran easily disproportionates to the corresponding [[dihydropyran]] and the [[pyrylium]] ion, which is easily hydrolyzed in aqueous medium.

Although the pyrans themselves have little significance in chemistry, many of their derivatives are important biological molecules, such as the [[pyranoflavonoid]]s.{{cn|date=March 2025}}

The term pyran is also often applied to the saturated ring analog, which is more properly referred to as [[tetrahydropyran]] (oxane).  In this context, the [[monosaccharide]]s containing a six-membered ring system are known as [[pyranose]]s.

==See also==
* [[Benzene]]
* [[Pyranose]]
* [[Furan]]
* [[Furfural]]
* [[Pyridine]]
* [[Pyrone]]
* [[Thiopyran]]

==References==
{{reflist}}

[[Category:Pyrans| ]]


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