AbstractThe qualitative effect of ring strain on the reactivity of small ring systems is briefly reviewed. It is pointed out that nucleofugalities of groups cannot be measured for nucleophilic substitution but that such measurements are possible for activated eliminations. Application of the techniques for determination of nucleofugality to eliminative fission of small strained rings shows that nucleofugality is very greatly enhanced. The extent of enhancement cannot be determined for epoxides, but has been determined for cyclopropanes, the results showing that about 60% of the ring strain energy is released in the transition state of ring fission. Catalysis of ring fission requires very specific placement of proton donor groups;gem‐dimethyl substitution raises the enthalpy of the transition state for eliminative fission of cyclopropane