Sesquifulvalene or pentaheptafulvalene is a hydrocarbon in the fulvalene class with chemical formula C₁₂H₁₀. It is composed of linked cyclopentadiene and cycloheptatriene rings.

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Sesquifulvalene

Names
Preferred IUPAC name 7-(Cyclopenta-2,4-dien-1-ylidene)cyclohepta-1,3,5-triene
Other names Pentaheptafulvalene
Identifiers
CAS Number	1961-84-8 N[1]
3D model (JSmol)	Interactive image
ChemSpider	553644
PubChem CID	638082
CompTox Dashboard (EPA)	DTXSID701032988
InChI InChI=1S/C12H10/c1-2-4-8-11(7-3-1)12-9-5-6-10-12/h1-10H Key: JYRVSRMFQWYDGM-UHFFFAOYSA-N
SMILES C1=CC=CC(=C2C=CC=C2)C=C1
Properties
Chemical formula	C12H10
Molar mass	154.212 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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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 4n+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.^[2]

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