The electronic structure of oxygen and sulfur heterocycles

Abstract

The method of Pariser and Parr has been applied to furan, thiophene, and 1,4-dithiadiene with a minimum of additional approximations and assumptions. It is possible to reproduce the spectra, dipole moments, resonance energies and reactivities of these molecules with a small number of adjusted parameters, all of which have reasonable values. The 3 d orbitals of sulfur need not be explicitly considered but they may alter the valence state ionization potential of sulfur. A good deal of the previously predicted resonance energy of 1,4-dithiadiene disappears in the more sophisticated calculation. The very strong preference of furan for a-substitution is predicted and originates primarily in the inductive effect of the oxygen. The lesser specificity of thiophene is also predicted, in this case arising from the form of the wave functions.