Relaxation of ring strain by introduction of a double bond

Ring strains are relaxed by the cyclic orbital interaction between a π-bond and the σ-bonds on the saturated atoms in the rings. An effective relaxation by the π–σ* interaction occurs in the three-, four-, and five-membered silicon rings. Cyclotrisilene 2b, cyclotetrasilene 4b, and cyclopentasilene 6b have lower strains than those of the parent saturated analogs. However, the stabilization is less significant for the hydrocarbons.