Pyran

In chemistry, pyran, or oxine, is a six-membered heterocyclic, non-aromatic ring, consisting of five carbon atoms and one oxygen atom and containing two double bonds. The molecular formula is C₅H₆O. There are two isomers of pyran that differ by the location of the double bonds. In 2H-pyran, the saturated carbon is at position 2, whereas, in 4H-pyran, the saturated carbon is at position 4.

Pyran

2H-pyran 4H-pyran
Names
IUPAC name 2H-Pyran, 4H-Pyran
Other names 2H-Oxine, 4H-Oxine
Identifiers
CAS Number	289-66-7 (2H) Y 289-65-6 (4H) Y
3D model (JSmol)	(2H): Interactive image (4H): Interactive image
ChemSpider	161812 (2H) Y 119912 (4H) Y
PubChem CID	186148 (2H) 136135 (4H)
UNII	CH5P2A5WTT Y
CompTox Dashboard (EPA)	DTXSID401349138 DTXSID80893659, DTXSID401349138
InChI (2H): InChI=1S/C5H6O/c1-2-4-6-5-3-1/h1-4H,5H2 Key: MGADZUXDNSDTHW-UHFFFAOYSA-N (4H): InChI=1S/C5H6O/c1-2-4-6-5-3-1/h2-5H,1H2 Key: MRUWJENAYHTDQG-UHFFFAOYSA-N
SMILES (2H): C1=CC=CCO1 (4H): C1=CCC=CO1
Properties
Chemical formula	C5H6O
Molar mass	82.102 g·mol−1
Related compounds
Related compounds	Dihydropyran Tetrahydropyran
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

4H-Pyran was first isolated and characterized in 1962 via pyrolysis of 2-acetoxy-3,4-dihydro-2H-pyran.^[1] It was found to be unstable, particularly in the presence of air. 4H-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 pyranoflavonoids.

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 monosaccharides containing a six-membered ring system are known as pyranoses.