Modèles en chimie théorique, développements et applications

Trois thèmes de recherche sont présentés dans ce travail.Les pseudo potentiels moléculaires développés dans le cadre de ce travail sont des potentiels développé&s pour des atomes hybridés. Le cas de l'atome de carbone sp2 est développé, que ce soit pour l'atome seul ou pour l'atome en interaction avec d’autres atomes portant ou non des pseudo potentiels. Grâce à ce travail, il est possible de reproduire avec précision la spectroscopie de polyènes, d'hydrocarbures polycycliques aromatiques et de molécules plus petites mais plus complexes. Finalement, un pseudo potentiel est développé pour un pseudo atome lié par une vrai liaison sigma.Le second thème de recherche est le développement de l'application HuLiS qui permet de développer une structure électronique délocalisée (par exemple une solution obtenue par la méthode de Hückel) sur une base de structures localisées, quelles soient de Lewis et/ou de Valence Bond.Enfin, une application de chimie théorique est présentée. Il s'agit d'une interaction avec deux groupes d'expérimentateurs qui a permis de comprendre pour quoi le trans-1,2-disiloxybenzocyclobutène capture le dioxygène triplet alors que cette réaction est interdite de spin

Atomic pseudopotentials for reproducing π-orbital electron behavior in sp 2 carbon atoms

International audienceA pseudo-potential system for an sp 2 carbon atom is built and tested as a building block for various pseudo-hydrocarbon polyenes and polycyclic aromatic hydrocarbons. This pseudo-system has a central charge of Z = 1, it contains only one electron. It is employed in ab-initio calculations in which several physical characteristics including the orbital energies and first ionisation energy, as well as first excitation energy and UV spectra, are found to be well-reproduced by the pseudo-system. Remarkably, not only are the π excitation energies in good agreement with the reference calculations, but also transition densities and intensities, confirming that the virtual space obtained with the pseudo-potentials is of excellent quality. Finally, this approach is capable of reproducing the π electron systems of small or large, planar or near-planar hydrocarbons at low computational cost

HuLiS, a program to teach mesomerism and more

International audienceThe HuLiS program is presented as a tool to decompose a delocalized wave function as a linear combination of localized electronic structures. The principles of the energy based HL-CI and the overlap based schemes HL-P are developed. The results obtained for a set of 10 relevant organic molecules are shown to compare very well with high level quantum chemistry calculations. A trust factor τ is introduced and its use is shown on the allyl radical case where symmetry must be taken into account

Mesomerism, Ring & Substituent Effects, A Computational Chemistry Experiments

International audienceThe introduction of computational chemistry experiments for undergraduate students in sciences can really facilitate knowledge acquisition. It can make consistent various concepts in chemistry without a lengthy experimental protocol involving synthesis and physical chemistry mesurements. In the present case the students use a very simple molecular modeling program that we implemented: HuLiS. The computational chemistry experiment described herein is devoted to an important concept in chemistry: resonance between Lewis structures (mesomerism). In this context, conjugated ring species, as herein, are somewhat specific in the sense that aromaticity can play an important role. Hence, we discuss here a rather advanced resonance effect, where the usual qualitative rules do not suffice by themselves, but aromaticity and the ―4n+2 electron‖ rule must be considered. This Hückel rule can be numerically displayed with an appropriate computational experiment. We use our free java applet (HuLiS) designed to evaluate the weights of resonance structures. As it is based on Hückel theory, the computations are fast, and the theoretical background is much simpler than with ab initio programs, hence the teachers are likely to master the tool used by the students. Upon substitutions, the weights of the zwitterionic Lewis structures adapt to the electronegativity. This is an opportunity to discuss the role of electronegativity in mesomerism, and strengthen the knowledge of the students

Exhaustive Generation of Benzenoid Structures Sharing Common Patterns

Benzenoids are a subfamily of hydrocarbons (molecules that are only made of hydrogen and carbon atoms) whose carbon atoms form hexagons. These molecules are widely studied both experimentally and theoretically and can have various physicochemical properties (mechanical resistance, electronic conductivity, ...) from which a lot of concrete applications are derived. These properties can rely on the existence or absence of fragments of the molecule corresponding to a given pattern (some patterns impose the nature of certain bonds, which has an impact on the whole electronic structure). The exhaustive generation of families of benzenoids sharing the absence or presence of given patterns is an important problem in chemistry, particularly in theoretical chemistry, where various methods can be used to better understand the link between their shapes and their electronic properties. In this paper, we show how constraint programming can help chemists to answer different questions around this problem. To do so, we propose different models including one based on a variant of the subgraph isomorphism problem and we generate the desired structures using Choco solver

Trans-1,2-disiloxybenzocyclobutene, an adequate partner for the auto-oxisation: EPR/spin trapping and theoretical studies

International audienceThe auto-oxidation of trans-1,2-disiloxybenzocyclobutene was found to be very efficient, giving endoperoxide in quantitative yield. Each step of the mechanism of spin-forbidden addition of triplet oxygen O2 was studied by both EPR/spin trapping and theoretical studies

An embedding technique based on a strategic use of atomic pseudo potentials

International audienc

Oxydation du benzocyclobutène.

Résumé graphique de l'article intitulé "Reply to the ‘Comment on “trans-1,2-Disiloxybenzocyclobutene, an adequate partner for the auto-oxidation: EPR/spin trapping and theoretical studies”’ by H.-G. Korth, P. Mulder and T. Paul, Phys. Chem. Chem. Phys., 2017, 19 , C6CP04187F