Alexei N. Pankratov

A semiempirical quantum chemical testing of thermodynamic and molecular properties of arsenic compounds

Abstract By the PM3 methods, standard values of entropy, heats and Gibbs energies of formation, first ionization potentials and dipole moments of the molecules have been computed for 65 inorganic and organic arsenic compounds. Linear dependences P exper = bP theor (where P is any of the mentioned properties) have been stated, allowing a priori evaluation of thermodynamic and molecular characteristics of As-containing substances. It has been shown that for arsine the PM3 method overestimates gaseous-phase proton affinity not more than by 10%. Triphenylarsinedichloride existence in benzene solution in the form of trigonal bipyramid with two axial chlorine atoms has been concluded.

Correlations between the Basicity and Proton Affinity of Substituted Anilines

The enthalpies and free energies of gas-phase proton affinity (PA) of aniline and 62 derivatives with different electron donor and electron acceptor substituents in the aromatic ring and at the nitrogen atom were calculated by the PM3 technique. Linear correlations between the shapes of pKa and PA have been found. The deviation of data from the above dependences for ortho-substituted anilines are discussed in the light of possible hydrophobic hydration of molecular fragments near the protonation reaction center.

Semiempirical quantum chemical methods: testing of thermodynamic and molecular properties of cyclic non-aromatic hydrocarbons and unsaturated heterocycles

Abstract Using the semiempirical all-valence MNDO, AM1 and PM3 methods, standard values of entropy, heats and Gibbs energies of formation, first ionization potentials and dipole moments of the molecules have been calculated for two series of compounds: 90 monocyclic and condensed bi-, tri- and polycyclic non-aromatic hydrocarbons and spirocyclic ones, 148 three-, five-, six- and seven-membered nitrogen-, oxygen-, sulphur-, selenium- and boron-containing unsaturated heterocycles. Linear dependences Pexper=bPtheor (where P is any of the mentioned properties) have been stated. Deviations from the above correlations have been noted. Similar data for the combined sequence containing substances of the above series, as well as for 64 acyclic and aromatic compounds with various functional groups, have been analysed.

Group Electronegativities, Inductive and Mesomeric Parameters from Semiempirical Quantum Chemical Computations

Summary. Electronegativities, inductive parameters, and mesomeric dipole moments have been computed for different substituents X in CH3X, XCH2COOH, n-C5H11X, C6H5X, 4-X-C6H4NH2, 4-X-C6H4NO2, 2,6-di-X-C5H3N, and 2,6-di-X-C5H3N+CH3. The applicability of several semiempirical quantum chemical method to such calculations is demonstrated, and the dependence of the heuristic quantities on the nature of the substituents X is reported.Zusammenfassung. Elektronegativitäten, induktive Parameter und mesomere und mesomere Dipolmomente wurden für verschiedene Substituenten X in CH3X, XCH2COOH, n-C5H11X, C6H5X, 4-X-C6H4NH2, 4-X-C6H4NO2, 2,6-di-X-C5H3N und 2,6-di-X-C5H3N+CH3 berechnet. Die Anwendbarkeit einiger semiempirischer quantenchemischer Methoden auf solche Problemstellungen wird gezeigt, und die Abhängigkeit der berechneten Größen von den Eigenschaften der Substituenten X wird diskutiert.

SEMIEMPIRICAL QUANTUM CHEMICAL METHODS : TESTING OF PHYSICOCHEMICAL PROPERTIES OF ACYCLIC AND AROMATIC COMPOUNDS

Abstract By the semiempirical all-valence MNDO, AM1 and PM3 methods, standard values of entropy, heats and changes in isobaric-isothermal potentials of formation, first ionization potentials and dipole moments have been calculated for 64 compounds belonging to the CH 3 X, n - C 5 H 11 X and C 6 H 5 X series. Linear dependences P exper = bP theor (where P is any of the mentioned properties) have been stated. Deviations from the above correlations have been noted.

Electrophilic aromatic substitution regioselectivity for benzene derivatives in terms of cationic localization energies from semiempirical quantum chemical computations

Abstract Cationic localization energies (Λ+) for the interaction of monosubstituted benzenes with nitronium cation have been computed by the PM3 method. Yields (Y) of nitration isomeric products correlate linearly with the Λ+ values. The lnY=a+bΛ+ expressions agree both with Arrhenius equation and with linear free energy relationships.

Thermodynamic Properties and Molecular Dipole Moments of Antimony Compounds from Quantum Chemical Evaluations

By the PM3 method, standard values of entropy, heats and Gibbs energies of formation and dipole moments of the molecules have been computed for a series of inorganic and organic antimony compounds. Linear dependences P exper = bP theor (where P is any of the mentioned properties) have been stated, allowing a priori evaluation of thermodynamic characteristics and molecular dipole moments of Sb-containing substances. It has been concluded that triphenylstibinedichloride in benzene solution, as well as triphenylstibinehydroxychloride in dioxane medium, exist in the form of trigonal bipyramid with two axial chlorine and oxygen atoms.

Tautomerism, protonation regioselectivity of 2-pyrrolidone and its complexation with palladium(II): an insight from the viewpoint of quantum chemistry

It has been established (AM1, PM3, RHF/6-31G**, MP2/6-31G**//RHF/6-31G**) that in the gaseous phase and in aqueous solution, the most thermodynamically stable tautomer of 2-pyrrolidone is lactame. According to PM3 evaluations with an explicit accounting for aqueous medium, the state of tautomeric equilibrium serves as a prerequisite to participation of 2-pyrrolidones lactime tautomer (pyrroline-2-ol) in complexation with palladium(II) in aqueous solution. 2-Pyrrolidone protonation in the gaseous phase and in aqueous medium has been shown to proceed via the oxygen atom, corresponding to expectations on mesomeric displacement of electron density in the amide fragment. The aqueous medium stabilizes 2-pyrrolidones lactime tautomer to a greater extent than for lactame, and an O-protonated cyclic amide compared to an N-protonated one. The stereodirective character of palladium(II) complexation with chloride ion and pyrroline-2-ol has been explained. The initially formed tetragonal–pyramidal adduct with an axial organic ligand rearranges into a precursor of the cis product, an intermediate with an extra coordinated axial chlorine atom. The less thermodynamically stable cis isomer of [PdCl2(pyrroline-2-ol)2] appears because its precursor is a lower energy intermediate of associative nucleophilic substitution. At a supramolecular level, cis product is capable of being stabilized by means of intermolecular dipole–dipole association in a crystal.

A brief guide to mycology web resources

Purpose – The purpose of this paper is to summarize the information about web resources in the area of mycology, one of the most important spheres of biology.Design/methodology/approach – The information on mycological web resources is systematised. Scientific journals, newsletters and magazines of mycological scope, along with their publishers, are presented.Findings – It is of use to biologists, chemists and other scientists and teachers working in the area of mycology, as well as scientists, who profess to disseminate scientific knowledge, to avail themselves of the myriad information sources on offer.Originality/value – This is possibly the first attempt to embrace comprehensively and in minute detail the vast field of information on the sources of contemporary mycology and its representative bodies.

A Quantum Chemical Study of Bismuth Compounds Thermodynamic Properties and Configuration of Pentacoordinated Organobismuth Molecules

By the PM3 method, standard values of entropy, heats, and free energies of formation have been computed for a series of inorganic and organic bismuth compounds. Linear dependences P exper = b P theor (where P is any of the mentioned properties) have been stated, allowing a priori evaluation of thermodynamic characteristics of Bi-containing substances. A quantum chemical calculation reproduces well the adiabatic ionization potential of BiH 3 . Triphenyldichlorobismuth and triphenyldinitratobismuth existence in benzene solutions in the form of trigonal bipyramid with two axial chloro and nitrato ligands has been concluded.