spiropentane
{{Chembox
| verifiedrevid =
| ImageFile = Spiropentane.svg
| ImageSize = 200px
| ImageFile2 = Spiropentane-from-xtal-view-4-3D-bs-17.png
| PIN = Spiro[2.2]pentane
| OtherNames =
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 157-40-4
| ChemSpiderID = 8734
| PubChem = 9088
| SMILES = C1CC12CC2
| StdInChI=1S/C5H8/c1-2-5(1)3-4-5/h1-4H2
| StdInChIKey = OGNAOIGAPPSUMG-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
| C=5 | H=8
| Appearance =
| Density =
| MeltingPtC = -134.6
| BoilingPtC = 39.0
| Solubility = }}
|Section3={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt = }}
}}
Spiropentane is a hydrocarbon with formula {{chem2|C5H8}}. It is the simplest spiro-connected cycloalkane, a triangulane.{{cite journal|last1=Donohue|first1=Jerry|last2=Humphrey|first2=George L.|last3=Schomaker|first3=Verner|title=The Structure of Spiropentane|journal=Journal of the American Chemical Society|volume=67|issue=2|year=1945|pages=332–335|issn=0002-7863|doi=10.1021/ja01218a056}}{{cite journal|last1=Murray|first1=M. J.|last2=Stevenson|first2=Eugene H.|title=SPIROPENTANE|journal=Journal of the American Chemical Society|volume=66|issue=2|year=1944|pages=314|issn=0002-7863|doi=10.1021/ja01230a515}}{{cite journal|last1=Murray|first1=M. J.|last2=Stevenson|first2=Eugene H.|title=The Debromination of Pentaerythrityl Bromide by Zinc. Isolation of Spiropentane1|journal=Journal of the American Chemical Society|volume=66|issue=5|year=1944|pages=812–816|issn=0002-7863|doi=10.1021/ja01233a047}}{{cite journal|last1=Price|first1=J.E.|last2=Coulterpark|first2=K.A.|last3=Masiello|first3=T.|last4=Nibler|first4=J.W.|last5=Weber|first5=A.|last6=Maki|first6=A.|last7=Blake|first7=T.A.|title=High-resolution infrared spectra of spiropentane, C5H8|journal=Journal of Molecular Spectroscopy|volume=269|issue=1|year=2011|pages=129–136|issn=0022-2852|doi=10.1016/j.jms.2011.05.011|bibcode=2011JMoSp.269..129P}}
It took several years after the discovery in 1887 until the structure of the molecule was determined.{{cite journal|last1=Philipow|first1=O.|title=Die Konstitution der Kohlenwasserstoffe Gustavsons: Vinyltrimethylen und Äthylidentrimethylen|journal=Journal für Praktische Chemie|volume=93|issue=1|year=1916|pages=162–182|issn=0021-8383|doi=10.1002/prac.19160930112|url=https://zenodo.org/record/1428058}}{{cite journal|last1=Faworsky|first1=Al.|last2=Batalin|first2=W.|title=Über das Vinyltrimethylen und Äthyliden-trimethylen von Gustavson|journal=Berichte der Deutschen Chemischen Gesellschaft|volume=47|issue=2|year=1914|pages=1648–1651|issn=0365-9496|doi=10.1002/cber.19140470250|url=https://zenodo.org/record/1426555}}{{Cite journal | doi=10.1366/000370272774351778|title = Infrared and Raman Spectra of Spiropentane-H8| journal=Applied Spectroscopy| volume=26| issue=5| pages=540–542|year = 1972|last1 = Burns|first1 = G. R.| last2=McGavin| first2=D. G.|bibcode = 1972ApSpe..26..540B|s2cid = 95384874}} According to the nomenclature rules for spiro compounds, the systematic name is spiro[2.2]pentane. However, there can be no constitutive isomeric spiropentanes, hence the name is unique without brackets and numbers.
Synthesis
After Gustavson produced cyclopropane by reacting {{chem name|1,3-dibromopropane}} with ground-up zinc metal, he tried the same reaction with {{chem name|2,2-bis(bromomethyl)-1,3-dibromopropane}} (see formula scheme). The starting material is easily obtained by reacting pentaerythritol with hydrobromic acid. A molecule with the formula {{chem2|C5H8}} was obtained. It was called {{chem name|vinyltrimethylene}} in the initial publication.{{cite journal|last1=Gustavson|first1=G.|title=Ueber Aethylidentrimethylen|journal=Journal für Praktische Chemie|volume=54|issue=1|year=1896|pages=104–107|issn=0021-8383|doi=10.1002/prac.18960540106|url=https://zenodo.org/record/1427990}} In 1907, Fecht expressed the assumption that it must be spiropentane, a constitutional isomer of vinylcyclopropane.{{cite journal|last1=Fecht|first1=H.|title=Über Spirocyclane|journal=Berichte der Deutschen Chemischen Gesellschaft|volume=40|issue=3|year=1907|pages=3883–3891|issn=0365-9496|doi=10.1002/cber.190704003194|url=https://zenodo.org/record/1426239}} Further evidence for the structure of the hydrocarbon comes from the fact that it could also be obtained from {{chem name|1,1-bis(bromomethyl)-cyclopropane}} (see formula scheme).{{cite journal|last1=Zelinsky|first1=N.|title=Über das Spirocyclan, seine Synthese und sein Verhalten bei der Reduktionskatalyse|journal=Berichte der Deutschen Chemischen Gesellschaft|volume=46|issue=1|year=1913|pages=160–172|issn=0365-9496|doi=10.1002/cber.19130460128|url=https://zenodo.org/record/1426495}}
:File:Spiropentane formation.svg
Spiropentane is difficult to separate from the other reaction products and the early procedures resulted in impure mixtures. Decades later, the production method was improved. The spiro hydrocarbon can be separated from the byproducts ({{chem name|2-methyl-1-butene, 1,1-dimethylcyclopropane, methylenecyclobutane}}) by distillation.{{cite journal|last1=Applequist|first1=Douglas E.|last2=Fanta|first2=George F.|last3=Henrikson|first3=Bertel W.|title=Chemistry of Spiropentane. I. An Improved Synthesis of Spiropentane|journal=The Journal of Organic Chemistry|volume=23|issue=11|year=1958|pages=1715–1716|issn=0022-3263|doi=10.1021/jo01105a037}}
Properties
= Physical properties =
Structural determination by electron diffraction showed two different C-C lengths; the bonds to the quaternary ("spiro") carbon atom are shorter (146.9 pm) than those between the methylene groups (CH2–CH2, 151.9 pm). The C–C–C angles on the spiro C atom are 62.2°, larger than in cyclopropane.G. Dallinga, R. K. van der Draai, L. H. Toneman, Recueil des Travaux Chimiques des Pays-Bas 87, 897 (1968).
= Chemical properties =
When heating molecules of spiropentane labelled with deuterium atoms, a topomerization or "stereomutation" reaction is observed, similar to that of cyclopropane: {{chem name|cis-1,2-dideuteriospiropentane}} equilibrates with {{chem name|trans-1,2-dideuteriospiropentane}}.J. J. Gajewski, L. T. Burka, Journal of the American Chemical Society 94, Nr. 25, 8857 (1972).
:File:Spiropentane isotopomer.svg
Gustavson (1896) reported that heating spiropentane to 200 °C caused it to change into other hydrocarbons. A thermolysis in the gas phase from 360 to 410 °C resulted in ring expansion to the constitutional isomer {{chem name|methylenecyclobutane}}, along with the fragmentation products ethene and propadiene.M. C. Flowers, H. M. Frey, Journal of the Chemical Society, 1961, 5550. Presumably, the longer – and weaker – bond is broken first, forming a diradical intermediate.
Related compounds
References
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{{Hydrocarbons}}