Applications of a simple molecular wavefunction. Part 2.—The torsional barrier in ethane

Abstract

The results of several calculations for the staggered and eclipsed forms of the ethane molecule using Frost's FSGO model are presented. In the first set of calculations one gaussian function was used for every electron pair, but in the second set two were used to represent the C—C bonding pair. Changes in the various components of the energy were determined and are discussed. The simple FSGO method gives a high value for the torsional barrier height but the second (double gaussian) calculation gave a good value.

It is concluded that it is important to include geometry changes when considering possible physical explanations of the barrier. The pattern of changes in the components of the energy, such as nucleus-electron attraction and electron-electron repulsion, is totally different when bond lengths and angles are allowed to change on rotation, compared to the energy changes that occur when the geometry is not allowed to relax.