ORBITAL INTERACTIONS AND CHEMICAL HARDNESS

Electron delocalization between molecules in chemical reactions is represented compactly in terms of the pairs of localized interacting orbitals. These interacting orbitals are illustrated to be reproduced approximately by projecting on to the occupied and unoccupied MO subspaces of an isolated reactant molecule a reference orbital function that has been chosen to specify the local characteristics of a given reaction. These projected reactive orbitals allow us to estimate the potential of an atom or a functional group for electron donation or electron acceptance in the reactant molecule. An analysis of the potential yields a novel view of orbital interactions that. they are governed by local electronegativity and local hardness of a structural unit and also by localizability of the interaction on the structural unit in each of the reagent and reactant parts. The localizability of the interaction is nothing but the Fukui function amplified oh the reaction sites. The physical significance of these terms is discussed in relation to the,types of chemical bonds to be formed in reactions.