Hückel Molecular Orbital Theory

Abstract

The H M O method is a simple but powerful approach toward ex plaining the stabilities, physical properties, and chemical reactivities of organic π-systems. The σ-electronic frameworks of these systems are relatively uninteresting in a theoretical sense since the properties of σ-bonds do not vary significantly from structure to structure. The H M O results that one can obtain easily are admittedly crude and approximate, being based on a num ber of gross assumptions or approximations. However, these results are capable of explaining and predicting a large am ount of interesting chemistry and seldom if ever give answers that are clearly in disagreement with either chemical experience or chemical intuition.If we start with the equationin which is the electronic Hamiltonian operator, including all electronic and nuclear interaction terms, this is completely insoluble for any organic molecule containing π-electrons (recall the form of this operator for ethylene). Therefore, it is necessary to make several basic assumptions and to use Postulate V to obtain approximate "eigenvalues" and approximate "eigenfunctions" for these π-systems. 27 II Hückel Molecular Orbital TheoryUsing Postulate V, we have for each ij/j J dx <Ej> =

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