The Variable Electronegativity Method. V. Pyridine, the Pyridinium Cation, and the Evaluation of Core-Attraction Integrals

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Abstract
A study of pyridine and the pyridinium cation by the VESCF method is reported. Several different methods of evaluating core attractions and electron repulsion integrals have been tried to determine their effect on the resultant energies and orbitals. Satisfactory results for the π-electron distribution and molecular dipole moment of pyridine are obtained. Values of ionization potentials are little better than those given by other theoretical methods and the variable electronegativity technique does not appear to improve the theoretical treatment of ultraviolet spectra. H�ckel MO parameters, evaluated from the VESCF matrix elements, accord with values found in similar studies of other heterocycles and also with values of parameters found necessary to account for the chemical properties of quinoline.