Calicene

Calicene or triapentafulvalene is a hydrocarbon of the fulvalene class with chemical formula C₈H₆, composed of a cyclopentadiene ring and a cyclopropene ring linked by a double bond. Its name is derived from the Latin calix meaning "goblet", from its shape.

Calicene

Names
Preferred IUPAC name 5-(Cycloprop-2-en-1-ylidene)cyclopenta-1,3-diene
Other names Triapentafulvalene
Identifiers
CAS Number	6249-23-6
3D model (JSmol)	Interactive image
ChemSpider	26537418
PubChem CID	12302244
CompTox Dashboard (EPA)	DTXSID60486629
InChI InChI=1S/C8H6/c1-2-4-7(3-1)8-5-6-8/h1-6H Key: ZXWMPJFQZJXFQN-UHFFFAOYSA-N
SMILES C1(C=CC=C1)=C2C=C2
Properties
Chemical formula	C8H6
Molar mass	102.136 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

Properties

Very high resonance energy is predicted by the Hückel method,^[1] however its resonance energy is not high. The central double bond is polarized with a partial positive charge on the carbon atom of triangular ring and a partial negative charge on the carbon atom of pentagonal ring, in keeping with added Hückel's rule stability of rings containing 2 π electrons and 6 π electrons respectively. Calicene's dipole moment has been computed to be 4.66 D.^[2] Several compounds that contains two or more calicene subunits are aromatic, such as trans-bicalicene^[2] (ring compound) or poly-2,7-[N]calicenes (chain compound)^[3]

Despite several attempts to prepare it, the parent calicene has so far defied attempts at synthesis.^[4] However, 1,2,3,4,5,6-hexaphenylcalicene has been prepared and an experimental dipole moment of 6.3 D was measured.^[5]