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: AIR^2– > BH^2– > CH^– > NH > S the electron density on the antipodal skeletal atom decreases proportionally in the tangential p_x and p_y(π) atomic orbitals and increases in the radial p_z 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.