A Reexamination of the Walsh‐ and Förster—Coulson—Moffitt‐ (F.C.M.) Orbital Concept, and its Relevance for the Interpretation of PE Spectra

Abstract

AbstractContrary to what is often believed, the description of the bonding orbitals of cyclopropane in terms of the so‐called Walsh‐orbitals or F.C.M.‐ (bent‐bond) ‐orbitals is not equivalent. These two sets of orbitals transform into each other only if their antibonding counterparts are taken into account. The bent‐bond orbitals can be obtained directly from the set of occupied canonical SCF orbitals of cyclopropane via a unitary transformation into localized orbitals. In contrast, the bonding Walsh‐orbitals are not contained in the occupied manifold of the canonical orbitals, because of their non‐equivalence to the F.C.M.‐ orbitals. This is the reason why the anti‐bonding Walsh‐orbitals have to be taken into consideration if one wants to draw valid conclusions, e.g., about the photoelectron spectra of compounds containing the cyclopropane moiety.