GROUND STATES OF CONJUGATED MOLECULES .12. IMPROVED CALCULATIONS FOR COMPOUNDS CONTAINING NITROGEN OR OXYGEN

This paper describes an extension of the completely self-consistent treatment of part XI1 to conjugated molecules containing nitrogen or oxygen. In this the total heat of atomization is expressed as a sum of bond energies of localized σ bonds, the compression energies being calculated using Morse potential functions, and of the total π-bond energy, calculated by a semiempirical SCF MO method. The key parameters in this, i.e., the one-electron core resonance integrals βij, are found by the Dewar-Schmeising thermocycle method. Preliminary calculations in part VII had treated the σ-bond energies as additional parameters ; in order to use values corresponding to the thermocycle, we found it necessary to allow for the polarity of σ bonds. It is assumed that the formal charges (±δQ) on atoms X and Y due to polarity to a σ bond linking them are given by Q(IX – Iy), where Ix and Iy are Mulliken electronegativities and Q is a universal constant; the corresponding changes in the valence-state ionization potentials (W) are found from empirical relations between W and q. © 1969, American Chemical Society. All rights reserved.