Benzopyran

Benzopyran
Identifiers
254-04-6 N
ChemSpider 10651828 YesY
Properties
C9H8O
Molar mass 132.16 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Benzopyran is an polycyclic organic compound that results from the fusion of a benzene ring to a heterocyclic pyran ring. 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.[1] 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.

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)

See also

References

  1. ↑ Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. xxxv, 211, 214. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
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