Rebuttal to the Bickelhaupt–Baerends Case for Steric Repulsion Causing the Staggered Conformation of Ethane

Two tenets of qualitative MO theory suggest contradictory explanations of ethane torsional barriers, but only one stands up to rigorous examination (see energy level diagrams). Bickelhaupt and Baerends' defense of the neo-steric “four-electron destabilization” concept (right) is shown to be as illusory as its predecessors.