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Propellane

Names
IUPAC name Tricyclopentane
Identifiers
CAS Number	35634-10-7
3D model (JSmol)	Interactive image
ChemSpider	125285
CompTox Dashboard (EPA)	DTXSID20189149
InChI InChI=1S/C5H6/c1-4-2-5(1,4)3-4/h1-3H2Key: ZTXSPLGEGCABFL-UHFFFAOYSA-N
SMILES C1(C2)(C3)C23C1
Properties
Chemical formula	C5H6
Molar mass	66.103 g·mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Propellane is an organic compound, the simplest member of the propellane family. It is a hydrocarbon with formula C₅H₆ or C₂(=CH₂)₃. The molecular structure consists of three rings of three carbon atoms each, sharing one C-C bond.

Propellane is a highly strained molecule. The bonds of the two central carbon atoms have an inverted tetrahedral geometry, and the length of the central bond is 160 pm. The strength of that bond is disputed; estimates vary from 59–65 kcal/mol to no strength at all. The energy of the biradical state (without the central bond and unfilled central carbons) is calculated to be 80 kcal/mol higher. The compound is highly unstable, and at 114 °C it will spontaneously isomerize to 3-methylenecyclobutene with a half-life of 5 minutes. Its strain energy is estimated to be 102 kcal/mol (427 kJ/mol).

The type of bonding in this molecule has been explained in terms of charge-shift bonding

Synthesis

Propellane was first synthesized by K. Wiberg and F. Walker in 1982,. according to the following schema:

Sythesis begins with conversion of the 1,3-di-carboxylic acid of bicyclopentane 1 in a Hunsdiecker reaction to the corresponding dibromide 2 followed by a coupling reaction with n-butyllithium. The final product 3 was isolated by column chromatography at -30°C (!)

However, a much simplified synthesis was published by. It starts with dibromocarbene addition to the alkene bond of 3-chloro-2-(chloromethyl)propene 6 followed by deprotonation by methyllithium and nucleophilic displacements in 7 not isolated but kept in solution at −196 °C.

Reactions

Acetic acid addition

Propellane spontaneously reacts with acetic acid to yield a methylenecyclobutane ester (4 above).

Polymerization

propellane undergoes a polymerization reaction where the central C-C bond is split and connected to adjacent monomer units, resulting the so-called staffanes.

A radical polymerization initiated by methyl formate and benzoyl peroxide results in a distribution of oligomers. An anionic addition polymerization with n-butyllithium results in a fully polymerized product. X-ray diffraction of the polymer shows that the connecting C-C bonds have bond lengths of only 148 pm

The compound 1,3-dehydroadamantane, which can be viewed as a bridged Propellane, also polymerizes in a similar way.

See also

• -Propellane
• -Propellane

References

1. Wei Wu, Junjing Gu , Jinshuai Song , Sason Shaik , Philippe C. Hiberty (2009), The Inverted Bond in Propellane is a Charge-Shift Bond. Angew. Chem. Int. Ed. volume 48, 1407–1410, doi:10.1002/anie.200804965
2. K. B. Wiberg, F H. Walker (1982), Propellane. J. Am. Chem. Soc. volume 104 issue 19, pp. 5239–5240; doi:10.1021/ja00383a046
3. J. Belzner, U. Bunz, A. D. Schlüter, G. Szeimies et al. "Concerning the synthesis of Propellane" Chem. Ber. volume 122, pp.397-398
4. (1998) Organic Syntheses, Coll. Vol. 10, p. 658 (2004); Vol. 75, p.98 Online article.
5. Piotr Kaszynski and Josef Michl (1988), Staffanes: a molecular-size "Tinkertoy" construction set for nanotechnology. Preparation of end-functionalized telomers and a polymer of propellane J. Am. Chem. Soc.; volume 110 issus 15, pp. 5225 - 5226; doi:10.1021/ja00223a070

• Cycloalkanes