Quelques Aspects de la Chimie Theorique Contemporaine

Abstract

AbstractIn this paper we make a survey of various aspects of theoretical chemistry to which we have made some contribution. Our Localized Molecular Orbital (LHO) approach to the electronic structure and reactivity of chemical species allowed us not only to generalize the Lewis and Linnett theories of valence but also to determine the mechanism of a wide variety of organic reactions. We have also proposed a general definition of the concept of stabilization energy applying to any compound. Using this concept, we have been able to elaborate a table of standard bond energy terms, to unify various notions such as hyperconjugation, resonance, ring strain and steric repulsion energy and to carry out a critical analysis of former definitions of the stabilization energy of olefines and free radicals. Furthermore, we have shown that the enthalpy changes and, eventually, the rate constants of any physical or chemical process involving paramagnetic or charged species could be rationalized in terms of their stabilization energies. In this prospect, we have proposed an original interpretation of the persistence of some free radicals and we have made interesting predictions concerning the thermochemistry and the kinetics of various reactions involving neutral or charged reactive intermediates. Moreover we have devised a semi‐empirical method for estimating the barrier heights of atom transfer reactions. So, we have been able to systematically determine the kinetic parameters of these processes using the transition state theory with an Eckart tunnelling correction. Finally, our barrier height modelling allowed us to interpret the effect of substituents on the activation barriers of hydrogen transfer reactions leading to carbon centred free radicals. On the whole, we have tried to demonstrate the promising role theory is presumably led to play in the development of modern chemistry, owing to the joint utilization of its own tools ‐ concepts, models and formalism ‐ and the information provided as much by experimental techniques as by the ab initio methods of quantum chemistry.