 The resulting steric strain causes such compounds to be unstable and highly reactive.The axial C-C bond is easily broken (even spontaneously) to yield less-strained bicyclic or even monocyclic hydrocarbons.Surprisingly, the most strained member [1.1.1] is far more stable than the other small ring members ([2.1.1], [2.2.1], [2.2.2], [3.2.1], [3.1.1], and [4.1.1]).