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Spiropentane is a
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 ) by
Gustavson (1896) reported that heating spiropentane to 200 °C caused it to change into other hydrocarbons. A 
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
with formula . It is the simplest spiro-connected cycloalkane
In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing ...
, a triangulane.
It took several years after the discovery in 1887 until the structure of the molecule was determined. According to the nomenclature rules for spiro compounds, the systematic name is spiro .2entane. However, there can be no constitutive isomeric spiropentanes, hence the name is unique without brackets and numbers.
Synthesis
After Gustavson producedcyclopropane
Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself ...
by reacting with ground-up zinc metal, he tried the same reaction with (see formula scheme). The starting material is easily obtained by reacting pentaerythritol
Pentaerythritol is an organic compound with the formula C(CH2OH)4. Classified as a polyol, it is a white solid. Pentaerythritol is a building block for the synthesis and production of explosives, plastics, paints, appliances, cosmetics, and many o ...
with hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. H ...
. A molecule with the formula was obtained. It was called in the initial publication. In 1907, Fecht expressed the assumption that it must be spiropentane, a constitutional isomer of vinylcyclopropane. Further evidence for the structure of the hydrocarbon comes from the fact that it could also be obtained from (see formula scheme).
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 ) by distillation
Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...
.
Properties
Physical Properties
Structural determination by electron diffraction showed two different C-C lengths; the bonds to the quarternary ("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 incyclopropane
Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself ...
.
Chemical Properties
When heating molecules of spiropentane labelled with deuterium atoms, a topomerization or "stereomutation" reaction is observed, similar to that of cyclopropane: equilibrates with .J. J. Gajewski, L. T. Burka,Journal of the American Chemical Society
The ''Journal of the American Chemical Society'' is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the ''Journal of Analytical ...
94, Nr. 25, 8857 (1972).
Gustavson (1896) reported that heating spiropentane to 200 °C caused it to change into other hydrocarbons. A thermolysis
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...
in the gas phase from 360 to 410 °C resulted in ring expansion to the constitutional isomer , along with the fragmentation products ethene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene is ...
and propadiene
Propadiene () or allene () is the organic compound with the formula . It is the simplest allene, i.e. a compound with two adjacent carbon double bonds. As a constituent of MAPP gas, it has been used as a fuel for specialized welding.
Production ...
.M. C. Flowers, H. M. Frey, Journal of the Chemical Society
The ''Journal of the Chemical Society'' was a scientific journal established by the Chemical Society in 1849 as the ''Quarterly Journal of the Chemical Society''. The first editor was Edmund Ronalds. The journal underwent several renamings, splits ...
, 1961, 5550. Presumably, the longer – and weaker – bond is broken first, forming a diradical intermediate.
References
{{Hydrocarbons Cyclopropanes Spiro compounds Polycyclic nonaromatic hydrocarbons