{{refimprove|date=August 2016}} {{Chembox |ImageFile = Pentaheptafulvalene.png |ImageSize = 200px |PIN = 7-(Cyclopenta-2,4-dien-1-ylidene)cyclohepta-1,3,5-triene |OtherNames = Pentaheptafulvalene |Section1 = {{Chembox Identifiers |CASNo = 1961-84-8 |CASNo_Ref = {{Cascite|changed|}}<ref>{{cite web |title=7-(2,4-Cyclopentadien-1-ylidene)-1,3,5-cycloheptatriene |url=https://webbook.nist.gov/cgi/cbook.cgi?Source=1975SCH%2F1099&Mask=400 |website=webbook.nist.gov |language=en}}</ref> |ChemSpiderID = 553644 |PubChem = 638082 |SMILES = C1=CC=CC(=C2C=CC=C2)C=C1 |StdInChI= 1S/C12H10/c1-2-4-8-11(7-3-1)12-9-5-6-10-12/h1-10H |StdInChIKey = JYRVSRMFQWYDGM-UHFFFAOYSA-N }} |Section2 = {{Chembox Properties |C=12|H=10 }} }}
'''Sesquifulvalene''' or '''pentaheptafulvalene''' is a hydrocarbon in the fulvalene class with chemical formula C<sub>12</sub>H<sub>10</sub>. It is composed of linked cyclopentadiene and cycloheptatriene rings.
==Properties== In the ground state, which is a singlet state, the central double bond is polarized, with a partial positive charge on the carbon atom of heptagonal ring and a partial negative charge on the carbon atom of pentagonal ring. This shift makes each ring have closer to 4''n''+2 π electrons, in keeping with the Hückel's pattern of aromatic stability. However, in the lowest quintet state, the central double bond is polarized with a partial negative charge on the carbon atom of heptagonal ring and a partial positive charge on the carbon atom of pentagonal ring due to Baird's rule.<ref>{{cite journal|author1=Christian Dahlstrand|author2= Martin Rosenberg|title=Exploration of the π-Electronic Structure of Singlet, Triplet, and Quintet States of Fulvenes and Fulvalenes Using the Electron Localization Function|journal= The Journal of Physical Chemistry A|date=2012|volume= 116|issue= 20|pages=5008–5017|doi=10.1021/jp3032397|pmid= 22536920|bibcode= 2012JPCA..116.5008D}}</ref>
== See also == * Tropone * Biphenyl
==References== {{reflist}} {{Hydrocarbon-stub}} Category:Fulvalenes