Pi-Electron Structure of Butadiene

The spectrum and structure of butadiene have been considered by application of several nonempirical methods to the problem of the energy levels of the π-electron system. Six spatial configurations of the nuclei have been treated, of which three correspond to the trans- form of the molecule and three, cis. The methods used include the use of antisymmetrized molecular orbitals with and without configuration interaction, electron-pair bonds, a model based on two neighboring vinyl radicals, and the method of atoms in molecules as applied to the preceding techniques. A comparison of the results given by the different theories permits an evaluation of the theories, at least in the case of unsaturation electrons.