The Variable Electronegativity Method. VI. Azulene

Abstract

Results of a variable-electronegativity SCF treatment of azulene, using the method used in previous VESCF studies, are reported. A slightly more elaborate method in which non-neighbour core resonance integrals are included has also been used. The π-electron distributions obtained by these methods correspond to dipole moments of 1.85 and 1.33 D respectively, the experimental value being about 1 D. The calculated bond orders accord with the rather incomplete experimental data on bond lengths. The π-electron densities account for the relative chemical reactivities of the azulene positions. The ionization potentials and proton magnetic resonance spectrum of azulene are also briefly considered. The concept of electronegativities of conjugated atoms in non-alternant systems is discussed in some detail on the basis of the VESCF results. It is shown that the assumption that the electronegativity of a carbon atom depends only on its π-electron density is an oversimplification for non-alternant systems.