Ludwik Komorowski

Electronegativity and hardness in the chemical approximation

Abstract The chemical electronegativity of an atom (Mulliken definition) has been identified with the average value of χ, the electronegativity function given by the rigorous density functional theory. An appropriate definition of hardness is developed, and a scale of hardness for bonded atoms is proposed. The electrodynamical atom model is demonstrated to produce a simple relation between atomic hardness and size. Electronegativity has been calculated for bonded atoms in a variety of molecules and crystals, covalent and ionic, without any specific approximation for the energy function E ( q ). Expressions for the electronegativity of a molecule have been derived and critically discussed.

Atomic Fukui function indices and local softness ab initio

The complete and original calculation scheme beyond the finite difference approximation, for the atomic (and orbital) Fukui function (FF) indices is proposed. The method explores an expansion for derivatives of LCAO coefficients, ∂C/∂N=CU. The separation scheme for the U matrix has been elaborated at the ab initio level. Nucleophilic and electrophilic FF indices, as well as atomic softness, have been derived from the standard result of SCF HF ab initio calculations. The indices reproduce two effects; the change in orbital occupancy and the relaxation of the electronic system. The molecular hardness (softness) provided by this scheme explicitly includes these two effects.

Empirical evaluation of chemical hardness

Abstract Two possible measures of hardness are proposed. An average chemical hardness is calculated separately for acidic and basic reactions of atoms. Differential hardnesses are derived from atomic radii.

Electronegativity through the energy function

Abstract The modern idea of electronegativity based on the E(q) function and the traditional chemical electronegativity are brought together in one self-contained expression. The electronegativity of a molecule is confronted with the in situ electronegativities of the component atoms.

Derivatives of Molecular Valence as a Measure of Aromaticity

Derivatives of the molecular valence have been calculated ab initio within the new non-finite-difference approach elaborated on earlier for the global hardness and the Fukui function indices. The group of 10 five-membered-ring molecules C4H4X has been chosen for a test, using the exaltation of the total magnetic susceptibility (Λ) as a reference measure of their aromaticity. An excellent correlation has been found between the molecular valence derivatives in the nucleophilic regime and the exaltation Λ, for both the aromatic and antiaromatic molecules. Calculation of the valence derivatives provides an absolute measure of aromatic character that is not directly dependent on the size of the molecule and does not require adopting any standard reference molecule.

NUCLEAR REACTIVITY AND NUCLEAR STIFFNESS IN DENSITY FUNCTIONAL THEORY

Abstract The nuclear reactivity has been identified with the derivative of the chemical potential (electronegativity) versus the deformation. A similar derivative of hardness has been proposed as a novel density functional theory index, nuclear stiffness. Both quantities have been calculated for a set of diatomic molecules. They provide information on the susceptibility of the molecule to attack in a collinear reaction.

Quantumchemical electronegativity and hardness indices for bonded atoms

Abstract An analysis of the electronegativity (χ A ) and hardness (η A ) of a bonded atom (A) is given on the ground of the Hartree-Fock Hamiltonian and based on Mulliken population analysis. Practical expressions for χ A and η A are developed within the Koopmans approximation. Electronegativity equalization (EE) has not been pursued, partial EE has been obtained, though. The resulting indices χ A and η A describe correctly atoms in simple molecules. The directional effect of the substituent in the benzene ring is properly rationalized and enhanced by means of the electronegativity and hardness of the ring carbons.

Polarization justified Fukui functions

New Fukui functions have been derived within the conceptual density functional theory by the analysis of the polarization effect of a system in static electric field. Resulting Fukui functions accurately reproduce the global softness and electronic dipolar polarizability; they meet the condition integral[f(r)/r]dr = -(partial differential mu/partial differential Z)(N) and lead to very reasonable values of the global hardness for atoms for the group of 29 main group elements. Computational clarity makes the new Fukui functions a promising tool in studies of molecular reactivity.

Fractionally charged ions in crystal lattices of organic ion-radical salts

Abstract The energy of an atom in a molecule is discussed on the basis of the definition of the chemical potential of electrons in a quantum system. An expression for the energy of the fractionally charged atom is proposed, and a master equation for the charge-dependent cohesive energy of a crystal is developed. Calculated net atomic charges in solid alkali halides are close to unity and their calculated cohesive energies indicate few percent of covalent bonding. The charge transfer at the energy minimum calculated for several organic, conducting ion-radical salts agree perfectly with the values determined experimentally. The lattice is found to be stabilized by the charge transfer, although the ionic interactions reproduce only part of the crystal cohesive energy.

Boron—nitrogen compounds : LXX. Boron derivatives of 3,3′-diaminodipropylamine☆

The reaction of borane(3) with 3,3′-diaminodipropylamine yields BH2B-bridge associated [3,3′-bis(dihydroborylamino)dipropylamino]dihydroborane, 1-aminopropyl-1,3,2-diazaboracyclohexane, or 1,8,10,9-triazaboradecalin (I), depending on the reaction conditions and the stoichiometry of the reactants. If tris(dimethylamino)borane is treated with 3,3′-diaminodipropylamine, only I or 1-bis-(dimethylamino)boryl-1,8,10,9-triazaboradecalin are obtained.