Ring Strain Energies from ab Initio Calculations

A new approach employing ab initio calculations is suggested for evaluating the strain energy of ring molecules as well as for estimating the relative contribution of different sources of strain to the ring strain energy. The approach developed is calibrated by reproducing experimentally determined strain energies of mono- and bicyclohydrocarbons, cyclic ethers, and amines. It is then used to predict ring strain energies of cyclic phosphoesters, hydrogen fluoride cyclic clusters, and magnesium dialdehyde cyclic chelates. The usefulness of the method is demonstrated in disclosing the role of ring strain in the enhanced reactivity of a five-membered cyclic phosphate relative to its acyclic analogue and six-membered ring counterpart.