Alternative theoretical model based on projection operators of atomic orbitals for description of the basic behavior of amines

Abstract

The HOMO- LUMO argument emerged as another interpretation of the reactivity. However, this concept can not be appropriate to describe the reactivity of certain chemical reactions. So, as the HOMO-LUMO approach has certain limitations, there is space for the emergence of new approaches like the FERMO concept. This new concept, based on chemical intuition and on criteria of composition and localization for correct determination of the frontier molecular orbital that regulates chemical reactions, can be understood as a complement to the argument HOMO–LUMO. So that the HOMO only will be the orbital that can modulate the reaction if it meets the requirements to be the FERMO. Thus, the objective of this work is to present a quantitative approach of the FERMO argument, through the analysis of the effective orbital reaction of 17 amines to determine which is the best orbital to describe the acid/base chemical reaction. To do that, a method was developed to quantify the location of a molecular orbital using projectors, based on which the degree of localization FERMO of the molecular orbital |(𝛷µ), which in turn is based on the standard of a projection operator based on atomic orbitals of the active site. 17 compounds were investigated in the form of a conjugated base. Those compounds were fully optimized with B3LYP/6-31g (d, p) with the Gamess software. Next, the developed algorithm was applied to generate coefficients that express the degree of localization of the various molecular orbitals in the space of the atomic orbitals. The quantitative data generated by the algorithm in point out that the FERMO approach descries better the acid-base behavior of the compounds investigated in relation to the usual HOMO-LUMO approach. In this line, the Fermo concept was success fully applied to describe the acid-base behavior of a series of amines, as demonstrated by the values of the coefficients provided by the new algorithm.