United atom models for polyatomic ligands. Part IV. Trisubstituted radical and anion derivatives of Group IV

Abstract

United atom theory is applied to radicals and anions AB₃ in which A is a Group IV element and B is H, CH₃, F, or Cl. Using available evidence and rules developed in previous work to predict orbital energies, the electronic structures and Lewis basicities of these fragments are discussed. Through a proposed subduction of the eigenvectors from T_d, the angular behaviour of all nla₁ and nle orbitals can be predicted. There are five different types of e orbitals from p, d, or f orbitals of the united atom, each implying its own natural bond angle, the smallest being associated with the orbital of lowest energy in any manifold. The affect of each type of e level on the pyramidal angle depends on its bonding character. In the hydrides this bond angle may be a measure of σ donation but in the heavier fragments it essentially reflects π basicity.