Cyclobutane, C4H8, is a four carbon alkane in which all the carbon atoms are arranged cyclically, hence cyclobutane.
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 circa 775 degrees Kelvin.
Melting point: -91°C Boiling point: 12.5°C