Because of the linear geometry of sp-hybridized C atoms, small and middle-sized rings with one or more C≡C triple bonds are highly strained. Small rings, in particular, considerably deviate from linearity. The distortion of the triple bond gives rise to a certain diradical character which manifests itself in higher reactivity, especially in regard to polymerizations and reactions with oxygen. Cycloheptyne is only stable in diluted solutions at low temperatures. Cyclooctyne is the smallest unsubstituted alkyne stable as pure compound at room temperature. It is a colorless liquid with a characteristic very intense and long-lasting unpleasant smell.