It is shown in this paper how the conventional naive semiempirical molecular orbital approach for conjugated hydrocarbons may be complemented by means of theoretically computed electron repulsion integrals in a manner suggested by the more rigorously founded SCF procedure. This is shown to give satisfying results in three examples with a considerable reduction in labor as compared to the complete ASMO method. The method is carried over in a natural and simple manner to substituted hydrocarbons, providing unambiguous methods of evaluating empirical resonance and inductive parameters. The concept of ``weak'' and ``strong'' substituent is developed and it is shown how these provide simple intuitive approaches to the estimation of interaction parameters in the theory. The inductive and resonance effects upon the energy levels are shown to be far from additive, and indeed are dependent upon each other. The dependence is analyzed and it is indicated which ones are important (and determinable) from various experimental situations.
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