Cyclobutane

Cyclobutane, C₄H₈, with a molecular mass of 56.107g/mol, is a four carbon alkane in which all the carbon atoms are arranged cyclically, hence cyclobutane. Cyclobutane is a gas and commercially available as a liquefied gas.

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Cyclobutanes are cyclobutane derivatives.

Conformation

The 90 degree bond angles between carbon atoms are significantly strained and as such have greater bond energies than either linear butane molecules or larger homocyclic alkanes such as cyclohexane. As such, cyclobutane is unstable above about 500 °C.

The chemical conformation of cyclobutane is not planar but folded or "puckered".^[1] One of the carbon atoms makes a 25° angle with the plane formed by the other three carbons. In this way some of the hydrogen eclipsing interactions are reduced. The confirmation is also known as a "butterfly".^[2] In substituted cycloalkanes both planar and puckered conformations exist. Because the energy difference between the two states can be small they can interconvert.

Cyclobutanes in nature

Despite inherent strain the cyclobutane motif is not an alien to molecules found in nature. One unusual example is pentacycloanammoxic acid which is a ladderane composed of 5 fused cyclobutane units. The estimated strain in this compound is 3 times that of cyclobutane. The compound is found in bacteria performing the anammoxprocess where it forms part of a tight and very dense membrane believed to protect the organism from toxic hydroxylamine and hydrazine involved in the production of nitrogen and water from nitrite ions and ammonia. ^[3] Some related fenestranes are also found in nature.

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