The 'Variable Electronegativity ' Method. II. Pyrrole

The properties of the p-electron system in pyrrole have been studied by a " variable electronegativity " self-consistent field molecular-orbital method and the results compared with those obtained by the conventional SCF procedure. The p-electron distribution calculated by the conventional SCF procedure cannot be satisfactorily reconciled with the observed dipole moment, but the distribution calculated by the VESCF method leads to a predicted dipole moment in good agreement with observation. Polarization of s-bonds makes a negligible contribution to the dipole moment.Derivation of the coulomb parameters for the simple Hückel molecular-orbital method from the VESCF results is considered and the factors responsible for auxiliary inductive effects are discussed. The p-electron ionization potential and the positions of the lowest excited states of pyrrole have been calculated by the VE method.