Global and local charge transfer in electron donor-acceptor complexes.

The formation of electron donor-acceptor complexes is studied with global and local charge transfer partitionings. The 1-parabola model is applied to the bromination reaction of alkenes and the correlations found between the global and local charge transferred with the transition energy of the charge transfer bands and the kinetic rate constants indicate that the nucleophilic attack of alkenes to bromine is the electronic process controlling the reactivity in the formation of the electron donor-acceptor complexes in this reaction. The 2-parabolas model is used in studying the nitrosation of aromatic compounds where colorful electron donor-acceptor complexes are formed. In this case, and like previous applications of the 2-parabolas model, the consistent usage of the model mandates the explicit consideration of reaction conditions in preparing the reactants to have a direction of electron transfer that is consistent with the chemical potential differences. For the nitrosation reaction this implies considering the nitrosonium cation as the charge acceptor. Both applications support that the charge transferred predicted from chemical reactivity models can be used as a scale to measure the nucleophilicity in reactivity trends. Graphical Abstract ᅟ.

Role of Reaction Conditions in the Global and Local Two Parabolas Charge Transfer Model.

The local and global charge transfer approach based on the two parabolas model is applied to several problems aiming to show the importance of incorporating the reaction conditions to evaluate the global and local chemical descriptors. It is shown that, by preparation of the reactants, the chemical potentials of the reacting species determined by the two parabolas model satisfy the condition for the transfer of electrons in the direction dictated by the chemical potential difference. The model is applied to the hydration of alkenes, showing that it recovers Markovnikov's rule, to aromatic nitration, and to the interaction of nitrobenzenes with 1,3-diethylurea, an electrochemically controlled hydrogen-bonding problem. The applications presented show that to satisfy the charge transfer directionality established by the chemical potential differences obtained from the two parabolas model, one has to incorporate the reaction conditions in the evaluation of the global and local chemical descriptors. The global and local charge transfer predicted along these lines allows one to determine the direction of electron transfer prevailing in the reaction and also the most relevant atoms participating in the interactions between the reactants, aiding in the unraveling of the chemical interactions present in the system under investigation.

Donation and back-donation analyzed through a charge transfer model based on density functional theory.

The net charge transfer process that occurs between two species, A and B, interacting with each other, may be decomposed into two processes: one in which A receives charge from B, which can be identified as the electrophilic channel for A or the nucleophilic channel for B, and a second in which A donates charge to B, which can be identified as the nucleophilic channel for A or the electrophilic channel for B. By determining the amount of charge associated with both processes through the minimization of the interaction energy associated with each case, the expressions for the amount of charge involved in each case can be expressed in terms of the directional chemical potentials and the hardnesses of the interacting species. The correlation between the charges obtained for the interaction between phosphine ligands of the type PRR'R'' and Ni, and the A1 carbonyl stretching frequency provides support for their interpretation as measures of the electrophilicity and nucleophilicity of a chemical species, and, at the same time, allows one to describe the donation and back-donation processes in terms of the density functional theory of chemical reactivity.