Strainless reference states for poly- and perfluorocycloalkanes: the ultradiagonal strain energy approach

It is well-established that the strain energy of cycloalkanes is affected by fluorination. While the strain energies of cyclopropane and cyclobutane are very nearly equal, perfluorination markedly increases the strain energy of the former and correspondingly decreases the latter. The numerical value for the strain energy of a given molecule is model-dependent. We discuss the strain energies of fluorinated cycloalkanes in terms of the “ultradiagonal” approach, a method earlier found useful for the understanding of fluorinated cyclopropanes and other species containing three-membered rings.