4H-1-Benzopyran

4H-1-Benzopyran is an organic compound with the formula C₆H₄C₃H₄O. It is one of two isomers of benzopyran, the other being 2H-1-benzopyran, which is more prevalent. It can be viewed as the fusion of a benzene ring to a heterocyclic pyran ring.^[1]

4H-1-Benzopyran

Identifiers
CAS Number	254-03-5 Y[PubChem]
3D model (JSmol)	Interactive image
Beilstein Reference	111589
ChEBI	CHEBI:35603
ChemSpider	119845 N
PubChem CID	136068
CompTox Dashboard (EPA)	DTXSID20180050
InChI InChI=1S/C9H8O/c1-2-6-9-8(4-1)5-3-7-10-9/h1-4,6-7H,5H2 Key: JCIDEANDDNSHQC-UHFFFAOYSA-N
SMILES C1C=COC2=CC=CC=C21
Properties
Chemical formula	C9H8O
Molar mass	132.162 g·mol−1
Appearance	colorless
Density	1.0732 g/cm3
Boiling point	80 °C (176 °F; 353 K) 13 Torr
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N (what is YN ?) Infobox references

"Benzopyran" redirects here. For the hydrocarbon group, see benzopyrene.

Some benzopyrans have shown anticancerous activity in vitro.^[2]

The radical form of benzopyran is paramagnetic. The unpaired electron is delocalized over the whole benzopyran molecule, rendering it less reactive than one would expect otherwise. A similar example is the cyclopentadienyl radical. Commonly, benzopyran is encountered in the reduced state, in which it is partially saturated with one hydrogen atom, introducing a tetrahedral CH₂ group in the pyran ring. Therefore, there are many structural isomers owing to the multiple possible positions of the oxygen atom and the tetrahedral carbon atom:

Structural isomers of chromene

2H-chromene (2H-1-benzopyran)	4H-chromene (4H-1-benzopyran)
5H-chromene	7H-chromene
8aH-chromene

Structural isomers of isochromene

1H-isochromene (1H-2-benzopyran)

3H-isochromene (3H-2-benzopyran)

Nomenclature

According to current IUPAC nomenclature, the name chromene used in previous recommendations is retained; however, systematic ‘benzo’ names, for example 2H-1-benzopyran, are preferred IUPAC names for chromene, isochromene, chromane, isochromane, and their chalcogen analogues.^[3] There are two isomers of benzopyran that vary by the orientation of the fusion of the two rings compared to the oxygen, resulting in 1-benzopyran (chromene) and 2-benzopyran (isochromene)—the number denotes where the oxygen atom is located by standard naphthalene-like nomenclature.

See also

• Benzofuran
• Benzopyrone