The effect of strain on reactivity has been subjected to much recent examination and a body of quantitative data bearing on this matter is now available.' In the case of intramolecular nucleophilic substitution by carbanions [eqn. (l)] it has been found2 that the enthalpies of activation for cyclisation are insensitive to the excess enthalpy'll-3 of the ring system being formed, at least in the region spanning 0-113 kJ mol-1. Gaoni4 has shown, however, that the inherent strain of a cyclic ...
