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The Fukui function is a frequently used DFT concept in the description of a system’s regioselective preferences to undergo electrophilic, nucleophilic, or radical attacks. Until now, this function has usually been evaluated using finite difference approximations. The first paper in this series proposed a method for obtaining the Fukui function by a direct calculation of the functional derivative of the chemical potential with respect to the external potential. This paper extends the method to condensed Fukui functions and applies it to an extensive testing set of molecules. Results are promising, which demonstrates the usefulness of the new formalism. [ABSTRACT FROM AUTHOR]

In an earlier publication, we suggested that the faster radiodefluorination kinetics of no-carrier-added ( S)-3-(2-[18F]fluoromethyl-phenyl)-2-amino-propionic acid (2-[18F]FMLP), as compared to 4-[18F]-fluoromethyl- l-phenylalanine (4-[18F]FMLP), was caused by an intramolecular interaction between the CH2F group on the 2-position of the phenyl ring and the ammonium group of the amino acid. As the presence of nonradioactive ( S)-3-(2-fluoromethyl-phenyl)-2-amino-propionic acid (2FMLP) in a concentration up from 10−6 mol/L reduces considerably the defluorination rate due to the formation of dimers, conventional experimental methods, like spectroscopy, cannot be performed for the study of the hydrolysis in no-carrier-added conditions occurring at a concentration range of about 5.0 10−10 mol/L. In the present study, we aim to provide a proof that supports aforementioned hypothesis as well as to establish a kinetic model and to put forward accompanying rate equations for this hydrolysis reaction by combining ab initio quantum chemical calculations and kinetic data. The calculations of the optimized geometries and the corresponding energies of the reactants involved in the hydrolysis of 2-[18F]FMLP and 4-[18F]FMLP were performed at the DFT[B3LYP/6-31++G**] level of theory. Interpretation of these data reveals that in 2-[18F]FMLP three intramolecular hydrogen bond interactions can be identified that are not present in 4-[18F]FMLP. The most important interaction is the one between the amino acid ammonium group and the benzylic fluorine atom, rendering the rupture of the CF bond much more favorable. These findings align with the experimental data and enabled us to put forward the rate expressions that define the unexpected pseudo-zero-order defluorination reaction of 2-[18F]FMLP at neutral pH. This study also proves that in the development of [18F]-benzylfluoride containing tracers present-day quantum chemical calculations are capable of predicting intramolecular interactions, affecting their reactivity toward hydrolysis at the no-carrier-added level. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 705-711, 2012 [ABSTRACT FROM AUTHOR]

In this contribution, we have investigated the performance of the initial hardness response, a reactivity index from conceptual DFT, in the prediction of the allowed or forbidden character of a series of sigmatropic hydrogen shifts, which are traditionally explained using the famous Woodward-Hoffmann rules for pericyclic reactions. Previously, it was observed that this quantity can be linked to the activation hardness of a chemical reaction and, in this case, thus to the aromaticity of the transition state in these kinds of reactions. It is shown, both by considering approximate reaction coordinates and intrinsic reaction coordinates that the allowed mode of the sigmatropic rearrangement corresponds to the largest value of the initial hardness response, in agreement with earlier work on cycloadditions and electrocyclizations. [ABSTRACT FROM AUTHOR]

We continue a series of papers in which the chemical importance of the linear response kernel χ(r,r') of conceptual DFT is investigated. In previous contributions (J. Chem. Theory Comput. 2010, 6, 3671; J. Phys. Chem. Lett. 2010, 1, 1228; Chem. Phys. Lett. 2010, 498, 192), two computational methodologies were presented and it was observed that the linear response kernel could serve as a measure of electron delocalisation, discerning inductive, resonance and hyperconjugation effects. This study takes the analysis one step further, linking the linear response kernel to the concept of aromaticity. Based on a detailed analysis of a series of organic and inorganic (poly)cyclic molecules, we show that the atom-condensed linear response kernel discriminates between aromatic and non-aromatic systems. Moreover, a new quantitative measure of aromaticity, termed the para linear response (PLR) index, is introduced. Its definition was inspired by the recent work published around the para delocalisation index (PDI). Both indices are shown to correlate very well, which emphasises the linear response kernel's value in the theoretical description of aromaticity.

This paper concerns the accurate description of the surface oxygen reactivity for the alkaline earth metal oxides using local DFT-based reactivity indices. The cumbersome periodic boundary conditions calculations, typically required to probe the reactivity of such systems, are avoided by the construction of a reliable cluster model. The standard Fukui function concept of conceptual DFT is generalized to include the contribution from not only the HOMO and the LUMO but also from other chemically relevant orbitals. Results prove that this approach is a valuable and straightforward alternative to the reactivity calculation of extended systems.

An alternative approach for the calculation of DFT-based reactivity descriptors involving derivatives of the energy with respect to the number of electrons and the external potential is further evaluated. Using functional derivatives with respect to the external potential, the finite difference approximation was avoided for the local calculation of the Fukui functions and the dual descriptor. A relevant set of molecules has been calculated after the optimization of computational parameters. It is shown that the new approach correctly predicts the nucleophilic attack on CH2O, the formation of CO metal complexes, the regioselectivity of monosubstituted benzenes, and the softest nucleophilic site in some ambident nucleophiles.

A simple method was recently proposed [D. J. Tozer and F. De Proft, J. Chem. Phys., 2007, 127, 034108] for performing explicit density functional theory (DFT) calculations on temporary anions. The excess electron in the anion is bound by a potential wall, the position of which is determined by a single parameter lambda, chosen to reproduce an approximate, theoretical negative electron affinity in the corresponding neutral. In the present study, the system-dependence of lambda and the sensitivity of the negative affinities to this parameter are investigated for 34 organic molecules. The results demonstrate that the system-dependent lambda values can be replaced by a global, average value, with minimal effect on the affinities. It follows that the orbitals, electron density, and other properties of a temporary anion can be determined from a single DFT calculation on that anion, using a large, diffuse basis set. As an illustration, singly occupied molecular orbitals and spin densities are determined for the anions of guanine and adenine nucleobases. Despite the use of a diffuse basis set, the method yields quantities that are localised in the molecular framework, associated with vertical electron affinities of -1.2 eV and -0.8 eV, respectively.

An important chemical property emerging from density-functional theory is the hardness, which can be evaluated as half of the difference between the vertical ionisation energy and electron affinity of the system. For many gas phase molecules, however, the electron affinity is negative and standard ways of evaluating this property are troublesome. In this contribution, we investigate an unconventional approximation for the electron affinity, based on the Kohn-Sham orbital energies of the frontier orbitals and the ionisation potential. It is shown that, for a large series of molecules possessing negative electron affinities, this methodology yields reasonable values for this quantity and that the correlation of the computed values with the experimental affinities from electron transmission spectroscopy is superior to other theoretical approaches. In a second part of this contribution, the hardness of a series of stable negative ions is evaluated in aqueous solution.