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In our continuous effort to retrieve the Woodward-Hoffmann rules from conceptual density functional theory (DFT), we have examined the last type of pericyclic reactions, i.e., chelotropic reactions. Both the initial hardness response and the dual descriptor have been investigated to predict the allowed and forbidden character for the addition of S[O.sub.2] to butadiene (4n system) and 1,3,5-hexatriene (4n + 2 system). It is shown that with both electronic descriptors, the conrotatory/disrotatory mode for the linear and nonlinear mechanisms are retrieved based on a density-only approach, free from consideration of orbital and (or) wave function symmetry. The dual descriptor moreover reveals that stabilizing interactions are presented only for the linear path, which can be considered as an overall favourable mechanism for a chelotropic reaction. Key words: chelotropic reactions, Woodward-Hoffmann rules, conceptual DFT. Dans le cadre de nos travaux pour recuperer les regles de Woodward-Hoffmann a partir de la theorie de la fonctionnelle de la densite conceptuelle, on a etudie le dernier type de reactions pericycliques, a savoir les reactions cheelotropes. On a etudie tant la reponse initiale de la durete que le descripteur dual pour predire le caractere permis et interdit pour l'addition du S[O.sub.2] sur le butadiene (systeme 4n) et hexa-1,3,5-triene (systeme 4n + 2). Il est demontre que pour les deux descripteurs electroniques, on peut retrouver le mode conrotatoire/disrotatoire pour les meecanismes lineiaires et non lineaires en se basant uniquement sur une approche de densite, sans prendre en consideration l'orbitale et (ou) la symetrie de la fonction d'onde. De plus, le descripteur double ne revele l'existence d'interactions stabilisantes que pour la voie lineaire qui peut etre consideree comme le meecanisme global le plus favorable pour une reaction cheelotrope. Mots-cles: reactions chelotrope, regles de Woodward-Hoffmann, theorie de la fonctionnelle de la densite; conceptuelle (<> conceptuelle). [Traduit par la Redaction], Introduction The Woodward-Hoffmann (WH) rules (1) have played an unprecedented role in predicting/rationalizing the outcome of chemical reactions on the basis of a quantum chemical approach. (2,3) Formulated in the [...]

The rotational barriers and conformational properties of the hydroxyl and mercapto groups attached to the alpha and beta positions of cyclohexa-2,5-dione and cyclohexa-2,5-dienthione is studied at the B3LYP/6-311++G(d,p) level of theory. The results reveal that the conformational preferences of these studied systems are the result of a subtle interplay between different competing effects.

Several molecular descriptors based on topological approaches as well as on a more traditional orbital-based decomposition, used to assess relations with hydrogen bond strengths in a series of formic acid dimers and its sulfur derivatives. A study devoted to the description of hydrogen-bond interactions through the use of few molecular descriptors is performed.

The 1, 3-intramolecular hydrogen transfer in the HSCH(O) reversible reaction (S)CHOH and HSNO reversible reaction SNOH reactions are studied through density functional theory calculations. The reaction force together with structural and electronic properties is monitored along the reaction path to characterize the mechanism of hydrogen transfer.

A new reactivity descriptor delta f(r) provides useful information on both stabilizing and destabilizing interactions between a nucleophile and an electrophile and helps to identify the electrophilic/nucleophilic behavior of a specific site within a molecule. It is shown that the new descriptor correctly predicts the site reactivity induced by different donor and acceptor groups in substituted phenyl molecules.

The formation of neutral copper clusters from dimer to nonamer is studied and rationalized using the experimental data of binding energies and electronic properties. An analytic expression for the binding energy as a function of the cluster size is proposed and used to predict the growth pattern of copper clusters.

An extension of the hammond postulate that includes structural information in the characterization of the Hammond or anti-hammond behavior of chemical reaction was studied. The theoretical development presented was strongly supported by the numerical results which allowed a complete characterization of different types of chemical reaction.

Research has been conducted on the benzhydryl cations. The theoretical electrophilicity pattern of these cations has been compared with the experimmental scale and the results demonstrate correlation between theoretical and experimental quantities.

The effects of continuum solvent on the electrophilicity index are examined, and solvation is found to enhance electrophilicity of neutral electrophilic ligands.

A theoretical study on the keto - enol tautomerism for a series of 10 acetyl derivatives CH3COX is presented. It was found that the hardness profiles show a minimum value close to the position of the transition structures where the energy shows a maximum.

A study of the formation of 10 bimolecular complexes from the combination of basic units of the type CHX-XH (X = O, S) is presented. The mechanism for double proton transfer was assessed through the force acting on the system to bring reactants into products.

An investigation of molecular vibrations in hydrogen sulfide and ammonia, and internal rotations in hydrogen peroxide, hydrogen persulfide, hydrogen thioperoxide and ethylene, is presented. It was found that conditions of maximum hardness and minimum polarizability complement the minimum energy criterion for molecular stability.

Research is presented demonstrating the rationalized behaviour of different intramolecular rearrangement reactions in terms of the principle of maximum hardness and the Hammond postulate.

A theoretical model of the relationships connecting the electronic, kinetic and thermodynamic properties of chemical reactions was developed based on the consistency between the principle of maximum hardness and the Hammond postulate. It is used to characterize reaction mechanisms and define the rate constants of chemical potential and hardness activation. A test of the model revealed that the activation process is regulated by the change in chemical potential and the relaxation process is regulated by the change in hardness when electronic properties are allowed to change along the reaction coordinate.

Research was conducted to examine a theoretical study of the internal rotation of HSOH. Ab initio calculations at the HF//6-311G level reveal that HSOH is a gauche molecule presenting a double-barrier torsional potential. Good estimations of barrier heights and properties associated with the stable isomer have been obtained. An important result is that the principle of maximum hardness is verified even though the electronic chemical potential varies along the reaction coordinate.

The reaction force F[R.sub.c] is analysed for an [S.sub.N] substitution reaction in the gas and aqueous phases. The preparative structural factors ([E.sub.act,tras]) are least affected but overall forward and reverse activation barriers are significantly lowered by the solvent and this example shows how the reaction force decomposition of activation barriers can help to elucidate the roles played by external factors.