The Alternant Hydrocarbon Pairing Theorem and All-Valence Electrons Theory. An Approximate LCOAO Theory for the Electronic Absorption and MeD Spectra of Conjugated Organic Compounds. 1

The significance of the pairing theorem for alternant hydrocarbons is demonstrated by a variety of experimental data, but standard all-valence electrons methods based on the »Neglect of Differential Overlap« (NDO) approximation fail to predict the observed pairing properties for this class of compounds. In this communication, a new all-valence electrons method is presented, using a basis of L6wdin orthogonalized atomic orbitals. This »Linear Combination of Orthogonalized Atomic Orbitals« (LCOAO) method is designed to predict the electronic absorption and magnetic circular dichroism data for organic :n: systems with particular emphasis on the pairing properties of alternants. Results for phenanthrene and hiphenylene are discussed.