![]() ![]() Most of these ideas have been gathered in a compact form within the framework of density functional theory (DFT). The basic quantities here are the molecular orbital coefficients and the intermolecular HOMO-LUMO gap.Įlectronic polarizability has been rather recently related to Pearson´s concept of chemical softness, thereby incorporating non electrostatic forces in the reactivity models based on electronic indexes. Within this approach, most of the determining factors governing a chemical reaction involved the frontier molecular orbitals HOMO and LUMO of the electron donor and the electron acceptor pair. This generalization was formally introduced in the theory of chemical reactivity, first by Klopman and Salem, and subsequently by Fukui, within a theoretical framework known as the Frontier Molecular Orbital (FMO) theory. Several local and non local reactivity indexes defined in the form of static density response functions, namely, atomic and bond polarizability, where proposed within this context. An elegant formulation based on Huckel molecular orbital (HMO) theory was presented in a series of seminal papers by Coulson et al, to describe the electronic structure of conjugated systems (mobile electron theory). These reactivity models were mainly framed on electron population analysis performed at each atomic center of the molecular system (gross and net atomic charges), as well as electron population at the internuclear regions (bond order indexes). From the dawn of Mullikens molecular orbital theory, the electronic structure of molecules has been the basis for the representation of static models of reactivity. The description of chemical processes in terms of reactivity indexes has become a current approach in theoretical physical organic chemistry. Some relationships between quantitative scales of reactivity and reaction mechanisms are discussed. ![]() These concepts are illustrated for a series of chemical reactions in Organic Chemistry, including electrocyclic processes, cycloadditions and electrophilic addition reactions. Site activation /deactivation may in turn be described by the variations in the local or regional patterns of reactivity, that may be induced by solvent effects or chemical substitution. While global responses, represented as derivatives of the electronic energy with respect to the total number of electrons quantitatively describe the propensity of a system to interconvert into another chemical species (chemical reactivity), the local counterparts assesses well those regions in the molecule where the reactivity pattern dictated by the global quantities is developed (selectivity). The use of these electronic indexes describing chemical interconversion is developed in this work along the perspective of the pioneering work conducted in Chile by the late Professor Fernando Zuloaga, to whom this article is dedicated in memoriam. Reactivity, selectivity and site activation are classical concepts in chemistry which are amenable to quantitative representation, in terms of static global, local and non local density response functions. (Received: SeptemAccepted: October 9, 2003) Universidad Andrés Bello, Santiago, Chile andĢ Departamento de Química, Facultad de Ciencias, Universidad de Chile, Santiago, Chile. ![]() Contreras 2ġ Departamento de Ciencias Químicas, Facultad de Ecología y Recursos Naturales, QUANTITATIVE REPRESENTATION OF REACTIVITY, SELECTIVITYĪND SITE ACTIVATION CONCEPTS IN ORGANIC Pérez 1, Julia Parra-Mouchet 2 and Renato R.
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