Electron spin correlation and the ethane barrier

Abstract
The barrier to rotation in ethane is discussed in terms of hydrogen-hydrogen exchange integrals properly weighted by experimentally determined bond orders. Such bond orders are proportional to the spin correlation of delocalized electrons as determined from nuclear magnetic resonance spin-spin coupling constants. The calculated value of 2·3 kcal per mole determined for the rotational barrier in ethane in this study is in good agreement with the experimentally determined value of 2·7–3·0 kcal per mole.