Acceptor Properties, Reorganization Energies, and π Bonding in the Boron and Aluminum Halides

Simple MO theory has been used to estimate the strength of π bonding in the planar, monomeric boron and aluminum halide molecules by partitioning the total energy of dissociation to valence state atoms according to relative values of σ and π overlaps. These π‐bond energies have been used to determine the energies required to reorganize the planar molecules to the pyramidal forms existing in their adducts with Lewis bases and the effects of these reorganization energies on the relative over‐all acceptor strengths of the halides is discussed. A number of independent checks indicate that the calculated energies are reasonable.