Calicene

Calicene
Names
	IUPAC name 5-(2-Cyclopropen-1-ylidene)-1,3-cyclopentadiene
	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

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.

Properties

A significant resonance effect is differing charge on the two rings, resulting in a highly polar structure.

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]

References

Schaad, L. J.; B. Andes Hess , Jr (2001). "Dewar Resonance Energy". Chemical Reviews. 101 (5): 1465–1476. doi:10.1021/cr9903609.
Oziminski, W. P.; M. Palusia (2013). "Capturing the elusive aromaticity of bicalicene". Physical Chemistry Chemical Physics. 15 (9): 3286–3293. Bibcode:2013PCCP...15.3286O. doi:10.1039/C2CP43426A. PMID 23358331.
Ratanadachanakin, Thawalrat; Collier, Willard E. R. (2015). "Aromaticity of a series of poly-2,7-[N]calicenes" (PDF). Maejo International Journal of Science and Technology. 9 (1): 21–31.
de Meijere, Armin (2014). Houben-Weyl Methods of Organic Chemistry Vol. E 17d, 4th Edition Supplement: Carbocyclic Three-Membered Ring Compounds, Cyclopropenes, Author Index, Compound Index. Stuttgart: Georg Thieme Verlag. p. 2967. ISBN 978-3131819741.
Agranat, Israel; Bergmann, Ernst D. (1965-01-01). "Hexaphenyltriapentafulvalene". Chemical Communications (London). 0 (21): 512–513. doi:10.1039/C19650000512. ISSN 0009-241X.

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[1] Schaad, L. J.; B. Andes Hess , Jr (2001). "Dewar Resonance Energy". Chemical Reviews. 101 (5): 1465–1476. doi:10.1021/cr9903609.

[bicalicene-2] Oziminski, W. P.; M. Palusia (2013). "Capturing the elusive aromaticity of bicalicene". Physical Chemistry Chemical Physics. 15 (9): 3286–3293. Bibcode:2013PCCP...15.3286O. doi:10.1039/C2CP43426A. PMID 23358331.

[3] Ratanadachanakin, Thawalrat; Collier, Willard E. R. (2015). "Aromaticity of a series of poly-2,7-[N]calicenes" (PDF). Maejo International Journal of Science and Technology. 9 (1): 21–31.

[4] Meijere, Armin (2014). Houben-Weyl Methods of Organic Chemistry Vol. E 17d, 4th Edition Supplement: Carbocyclic Three-Membered Ring Compounds, Cyclopropenes, Author Index, Compound Index. Stuttgart: Georg Thieme Verlag. p. 2967. ISBN 978-3131819741.

[5] Agranat, Israel; Bergmann, Ernst D. (1965-01-01). "Hexaphenyltriapentafulvalene". Chemical Communications (London). 0 (21): 512–513. doi:10.1039/C19650000512. ISSN 0009-241X.