4H-1-Benzopyran

{{More citations needed|date=January 2017}} {{DISPLAYTITLE:4''H''-1-Benzopyran}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = | Name = 4''H''-1-Benzopyran | ImageFile = 4H-Chromen.svg | ImageClass = skin-invert-image | PIN = 4''H''-1-Benzopyran |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|PubChem}} | CASNo = 254-03-5 | ChEBI = 35603 | Beilstein =111589 | ChemSpiderID = 119845 | ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} | PubChem = 136068 | StdInChI=1S/C9H8O/c1-2-6-9-8(4-1)5-3-7-10-9/h1-4,6-7H,5H2 | StdInChIKey = JCIDEANDDNSHQC-UHFFFAOYSA-N | SMILES = C1C=COC2=CC=CC=C21 }} {{Chembox Properties | C=9|H=8|O=1 | MolarMass = | Appearance = colorless | Density = 1.0732 g/cm3 | MeltingPt = | MeltingPt_notes = | BoilingPtC = 80 | BoilingPt_notes = 13 Torr | Solubility = }} }} {{redirect|Benzopyran|the hydrocarbon group|benzopyrene}}

'''4H-1-Benzopyran''' is an organic compound with the formula {{chem2|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.<ref>{{cite journal |doi=10.1021/cr500075s |title=Natural and Synthetic Chromenes, Fused Chromenes, and Versatility of Dihydrobenzo[ ''h'' ]chromenes in Organic Synthesis |date=2014 |last1=Pratap |first1=Ramendra |last2=Ram |first2=Vishnu Ji |journal=Chemical Reviews |volume=114 |issue=20 |pages=10476–10526 }}</ref>

Some benzopyrans have shown anticancerous activity ''in vitro''.<ref>{{cite journal|title=Mechanism of action of the third generation benzopyrans and evaluation of their broad anti-cancer activity in vitro and in vivo|journal=Scientific Reports|volume=8|issue=1|pages=5144|doi=10.1038/s41598-018-22882-w|pmid=29572477|pmc=5865165|year=2018|last1=Stevenson|first1=Alexander J|last2=Ager|first2=Eleanor I|last3=Proctor|first3=Martina A|last4=Škalamera|first4=Dubravka|last5=Heaton|first5=Andrew|last6=Brown|first6=David|last7=Gabrielli|first7=Brian G|bibcode=2018NatSR...8.5144S }}</ref>

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:

{|class=wikitable style="text-align:center;" |+Structural isomers of chromene |- | 120px 2''H''-chromene (2''H''-1-benzopyran) | 120px 4''H''-chromene (4''H''-1-benzopyran) |- | 5''H''-chromene | 7''H''-chromene |- | 8a''H''-chromene | |}

{|class=wikitable style="text-align:center;" |+Structural isomers of isochromene |- | 120px 1''H''-isochromene (1''H''-2-benzopyran) | 120px 3''H''-isochromene (3''H''-2-benzopyran) |}

==Nomenclature== According to current IUPAC nomenclature, the name '''chromene''' used in previous recommendations is retained; however, systematic ‘benzo’ names, for example 2''H''-1-benzopyran, are preferred IUPAC names for chromene, isochromene, chromane, isochromane, and their chalcogen analogues.<ref name="IUPAC2013">{{cite book | title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = The Royal Society of Chemistry | date = 2014 | location = Cambridge | pages = P001–P004 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4| chapter = Front Matter }}</ref> 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

==References== {{reflist}}

Category:Benzopyrans