Mechanism of the antipodal effect with borane cages
Abstract
With the EB11H11(1) and EB9H9(2) series, CNDO/2 and extended Hückel type calculations show that with decreasing electron density on the vertex E: AIR2– > BH2– > CH– > NH > S the electron density on the antipodal skeletal atom decreases proportionally in the tangential px and py(π) atomic orbitals and increases in the radial pz orbital through both series; this explains contradictory information about the electron density on the antipodal atom, a low electron density being indicated by the 11B NMR chemical shift and a high one being deduced from chemical behaviour.