Comparison of through-space and through-bond interactions in four-membered ring systems

Abstract

Numerous authors have discussed the interactions between nondirectly bonded functions in terms of direct “though-space” orbital interactions and/or “through-bond” orbital interactions. In this study, ab initio interaction energies are calculated for 1,3-located functions in the four-membered ring systems cyclobutane and all mono- and 1,3-diheterocyclobutanes obtainable with oxygen, sulfur, and carbonyl functions, systems in which the through-space interactions should be maximal due to the close proximity of the interacting functions. Through-space and through-bond interactions are separated from one another by performing the calculations both in the absence and in the presence of the methylene groups that indirectly bond together the 1- and 3-located functions. In all cases the through-bond interaction energies are found to be greater than the through-space interaction energies by factors ranging from 3- to 25-fold.