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n. (context chemistry English) Any of a class of heterocyclic compounds containing a ring of five carbon atoms and an oxygen atom; especially the simplest one, C5H6O.


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 CHO. 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.

4H-Pyran was first isolated and characterized in 1962 via pyrolysis of 2-acetoxy-3,4-dihydro-2H-pyran. It was found too 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.

Usage examples of "pyran".

I must go to Pyran and watch the life ebb slowly from him, praying for him to live, in spite of all his pain and torment, until we can make safe his country.

Djukich, the commander of the Earth forces, was a small man who appeared even smaller before the glowering strength of the Pyran personality.