Triaziridine and tetrazetidine vs. cyclic water trimer and tetramer: A computational approach to the relationship between molecular and supramolecular conformational analysis

The potential energy surfaces of cyclic water trimer and tetramer, as typical examples of supramolecular systems, have been compared with those of triaziridine and tetrazetidine, which can be considered as their suitable molecular analogues. The survey was performed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) level of theory and includes also the monomethyl and monofluoro derivatives of both the trimer and the tetramer. This comparison leads to the conclusion that supramolecular systems, where the molecular components are held together by weak interactions, exhibit the same conformational features as the analogous molecular compounds, where the constituent atoms are held together by strong covalent bonds. More importantly, even though in the former the energy required to induce conformational rearrangements is much smaller than that needed for typical molecular systems, there is a fairly good linear relationship between both magnitudes. We have also found that this quantitative relationship can be perturbed when the through-space interactions, either repulsive or attractive, between the substituents are sufficiently strong.