The Role of Ring Strain on the Ease of Ring Closure of Bifunctional Chain Molecules

The role of ring strain on the ease of ring formation over a wide range of ring sizes is discussed on the basis of a comparison of transition state versus product-ring strain energies. A general procedure is illustrated for the assessment of transition-state strain energies, based on experimental effective molarities (EMs) and an extra-thermodynamic treatment of entropy data for ring closure. It is found that the ring product is a good model of the transition state of cyclisation for all but the shortest chains. Our earlier interpretation of this remarkable lack of correspondence between transition state and product-ring strain energies in intramolecular nucleophilic substitutions of the very short chains, is compared with the results of recent theoretical calculations.