Spiropentane is a hydrocarbon 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 A triangulane is a hydrocarbon consisting exclusively of a series of spiro-linked cyclopropane rings. Triangulanes are named according to the rules of systematic nomenclature for spiro compounds. The pattern of their common names is " 'n''riangu ...

. 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 produced

cyclopropane 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 with hydrobromic acid. 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 formation

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.

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 in

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 94, Nr. 25, 8857 (1972). Spiropentane topomer

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 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, 1961, 5550. Presumably, the longer – and weaker – bond is broken first, forming a diradical intermediate. Spiropentane thermo

References

{{Hydrocarbons Cyclopropanes Spiro compounds Polycyclic nonaromatic hydrocarbons