Ring‐opening reactions. 6. eliminative ring fission of aziridinium and azetidinium ions

The reactivity ratio between the three‐ and four‐membered cyclic ammonium ions in ring‐opening elimination reactions was measured. The comparison with the analogous ratio obtained in a previous study on ring‐opening substitution reactions suggests a substantial difference in the effect of the stereochemical factors governing the two ring‐opening reactions and confirms the anomalous behaviour of small rings in the ring‐opening substitution reaction.