Electron Deficient Compounds. II. Relative Energies of ``Half-Bonds''

Abstract

It is suggested that the tendency to make use of all low energy orbitals is the underlying principle of electron‐deficient bonding. Simple theoretical arguments, limited to the special case of two electrons and three orbitals, are given to show that this principle is a direct consequence of quantum‐mechanical theories of valence. Two half‐bonds are shown to be of lower energy than a single bond plus an unused low energy orbital in most cases. The tendency to form half‐bonds should be most important in symmetrical cases, and particularly where the electronegativities of all atoms involved are equal, e.g., the boron hydrides and H₃⁺. Certain consequences of the proposal to the fields of organo‐metallic compounds, catalysis, and molecular rearrangements are pointed out. It is suggested that at low temperatures complexes may exist between molecules with excess orbitals and molecules with no unshared pairs.