Error of Atomic Charges Derived from Electrostatic Potential

The purpose of this article is to show that CHELP, CHELPG, and Merz and Kollman undergo error for the charge on atoms of HCOO^– (H₂O) _n for n = 1 6. We also demonstrate that the CHELP, CHELPG, and Merz and Kollman show error for the tendency toward change in the charges on carbons for CH₃NH⁺ ₃ (CH₃)₂NH⁺ ₂ (CH₃)₃NH⁺ (CH₃)₄N⁺.     

Metal bioaccumulation by the freshwater algaScenedesmus quadricauda

Bioaccumulation of six metals (Cu²⁺, Cu⁺, Mo⁶⁺, Mn²⁺, V⁵⁺, Ni²⁺) and their combinations by algaScenedesmus quadricauda was determined by using radio nuclide X-ray fluorescence (RXFA). The metals were added into the cultivation medium in concentrations corresponding with EC₅₀ value for each metal. The obtained results indicate that Ni²⁺, Cu²⁺ and Cu⁺ were accumulated in high amounts (20%, 17.5% and 15.19%) the Mo⁶⁺ ion (<0.2%) was accumulated in the lowest amount. For metal-metal interactions in accumulation of metal ions by algaS. quadricauda three types of answers were determined: inhibition (MoCu²⁺, Ni, Mn, V; VNi, Mn; MnNi, Cu²⁺, Cu⁺; Cu⁺Ni; Cu²⁺Ni; NiMn, V), enhancement (VCu⁺; Cu²⁺Mn;Cu⁺V, Mn; MnV; NiCu²⁺, Cu⁺) and neutral effect (VMo; Cu²⁺Mo; Cu⁺Mo; MuMo; NiMo).     

Laser-spectroscopic laboratory studies of atmospheric aqueous phase free radical chemistry

Nitrate radical (NO₃) reactions with benzene (R-1), toluene (R-2), p-xylene (R-3), p-cresol (R-4) and mesitylene (R-5) have been studied by laser photolysis/long path laser absorption (LP-LPLA) in aqueous solution. Rate constants of k₁=(4.0±0.6) 10⁸, k₂=(1.2±0.3)10⁹, k₃=(1.6±0.1)10⁹, k₄= (8.4±2.3)10⁸ and k₅=(1.3±0.3)10⁹ lmol^-1s^-1 were obtained at T=298 K. In addition, reaction rate coefficients for SO^-₅+Fe²⁺prod. (R-6) and SO^-₅+Mn²⁺prod. (R-7) of k₆=(4.3±2.4) 10⁷ lmol^-1s^-1 and k₇=(4.6±1.0)10⁶ lmol^-1s^-1 (T=298 K, I0) have been obtained by the application of laser photolysis/UV-VIS broadband diode array spectroscopy. A new laser photolysis/UV-long path laser absorption experiment has been applied to study the reaction of the Cl^-₂ radical anion with dissolved sulfur(IV). For the reactions Cl^-₂+HSO^-₃2Cl^-+H⁺+SO^-₃ (R-8) and Cl^-₂+SO^2-₃2Cl^-+SO^-₃ (R-9) rate coefficients of k₈=(1.7±0.2)10⁸ lmol^-1s^-1 (T=298 K, I0) and of k₉=(6.2±0.3)10⁷ lmol^-1s^-1 (T=279 K, I0) were obtained.     

Kinetics and mechanism of the decomposition of CS2, OCS,and SCl2 in a radiofrequency pulse discharge

The identification of transient species in r.f. discharges and measurement of rate coefficients for their reactions contributes to the understanding of the complex mechanisms in r.f. plasma chemistry. Using kinetic spectroscopy in conjunction with a short-duration r.f. pulse to investigate the decomposition of CS₂, OCS, and SCl₂ at low pressure, it has been shown that the predominant primary dissociation steps are CS₂CS+S, OCSCO+S(¹D), and SCl₂S+Cl+Cl. With OCS the most important subsequent steps involved the formation and removal of S₂: S(¹D)+OCSCO+S₂(a¹), S₂(a¹)+MS₂(X³)+M, (13), and 2S₂+MS₄+M(15). Taking the previously published value of k₁₂, computer simulation gave the rate coefficient values k₁₃=6.4±2.4×10⁸ mol^–1 dm³ s^–1 and k₁₅=1.8±0.5×10¹³ mol^–2 dm⁶ s^–1 at 295±3 K.     

Optical Properties of Thallium(I) Perrhenate. Thallium-Localized Phosphorescence

Summary. The salt Tl⁺ReO₄ ^– shows a strong luminescence at _max=400nm which originates from the lowest-energy sp triplet of Tl⁺. A low-energy Tl^IRe^VII metal-to-metal charge transfer excited state has not been observed.     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Cyclic voltammetric and e.s.r. studies of a tetraaza 14-membered macrocyclic copper(II) complex derived from 3-salicylideneacetylacetone ando-phenylenediamine: stabilization and activation of unusual oxidation states

Summary A 14-membered macrocyclic Schiff base derived from 3-salicylideneacetylacetone ando-phenylenediamine acts as a tetradentate and strongly conjugated ligand to form a cationic solid complex with CuCl₂. U.v.-vis. and e.s.r. spectral data reveal a strong ligand to metal -interaction in the square planar complex. C.v. data reveal that the title ligand is able to stabilize the copper(III) oxidation state more effectively than comparable saturated or partially unsaturated macrocyclic ligands and confers a weaker tendency for reduction of copper(II) to copper(I) and copper(0). While the inclusion of a PPh₃ ligand suppresses the Cu⁰ Cu^I Cu^II oxidation, imidazole and pyridine strongly enhance the Cu^II Cu^III oxidation of the complex.     

A probe of dynamical models using functional sensitivity densities with application to He++Ne(2p 6)→He++Ne(2p 53s) and Li+I→Li++I−

Summary The functional sensitivity densities ln ₁₂(E)/ lnV _ii (R) for He⁺+Ne(2p ⁶)He⁺+Ne(2p ⁵3s) reveal that the collisional excitation cross section ₁₂(E) is insensitive to the additional diabatic curveV ₃₃ included in some models. The negligible sensitivity of ₁₂(E) toV ₃₃ offers a quantitative validation of the more popular two state model for collisional excitation of Ne by He⁺. The sensitivity profiles for the collisional ionization Li+ILi⁺+I^– modeled by crossing diabatic curvesV ₁₁ (covalent) andV ₂₂ (ionic) shows that the ionization cross section does not depend on inner crossings even when these stem from large distortions in the underlying potential energy curves. The lack of sensitivity to inner crossings establishes the predominant role of the outermost crossing in triggering nonadiabatic transitions.     

Thermal decomposition of hydroxylammonium neodymium sulfate dihydrate

The thermal decomposition of hydroxylammonium neodymium sulfate dihydrate has been investigated by simultaneous thermogravimetry and differential thermal analysis. Chemical analysis, X-ray powder spectra and infrared spectroscopy have been employed to characterize the intermediates and the final product. The thermal decomposition can be described by the sequence (NH₃OH)Nd(SO₄)₂·2H₂O(NH₃OH)Nd(SO₄)₂ NH₄Nd₃(SO₄)₅Nd₂(SO₄)3. The first and the second reactions overlap, but the last one is well separated from the first two.     

The UV spectra of arsines and arsine selenides

Short-wavelength n_Se ^* and long-wavelength n_Se ^* bands are observed in the UV spectra of saturated trialkylarsine selenides in the near-UV region. The n_x ^* band in going from arsine selenides to arsine sulfide and then to arsine oxides is shifted hypsochromically, as in the corresponding phosphorus compounds. The n_x ^* band is only slightly sensitive to the chalcogen. Saturated trialkylarsines, in contrast to alkylphosphines, absorb in the near UV region (the n_As ^* band is at 208 nm).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 940–942, April, 1990.     

Recherches théoriques sur la structure électronique de molécules contenant des atomes hybridés en sp:

Résumé La théorie L. C. A. O. améliorée est appliquée à l'étude de la molécule C₃. Afin de satisfaire l'égalité nécessaire entre les éléments de matrice non diagonaux L _pq et L _qp, nous avons introduit un déplacement électronique le long des liaisons . Les charges nettes portées par les atomes terminaux sont: + 0,09. La distance C-C calculée (1,286 Å) est en bon accord avec l'expérience. Les énergies des deux premières transitions NV: ¹ _g ^{+ 1} _u ^– et¹ _g ^{+ 1}_u sont: 4,7 et 4,8 eV. Ces valeurs ne sont pas en contradiction avec l'expérience qui situe ces transitions au delà de 4,1 eV, limite à partir de laquelle l'absorption de l'atmosphère terrestre rend impossible l'étude des spectres cométaires.

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The improved LCAO theory is applied to the C₃ molecule. In order to satisfy the necessary equality between the non-diagonal matrix elements L _pq and L _qp, we have introduced an electron shift along the bonds. The net charges borne by the terminal atoms are: + 0.09. The computed C-C distance (1.286 Å) is in good agreement with experiment. The two first NV transition energies: ¹ _g ^{+ 1} _u ^– and ¹ _g ^{+ 1}_u are: 4.7 and 4.8 eV. These values are not in contradiction with experiment which places these transitions beyond 4.1 eV, limit from which the terrestrial atmospheric absorption makes impossible to study the comets' spectra.

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Zusammenfassung Die verbesserte LCAO-Theorie wird auf die C₃-Molekel angewandt. Um die nötige Gleichheit der nicht-diagonalen Matrixelemente L _pq und L _qp zu erhalten, haben wir eine Elektronenverschiebung längs der -Bindungen eingeführt. Die Ladungen der Endatome sind: + 0,09. Die berechnete C-C-Bindungslänge (1,286 Å) stimmt mit der Erfahrung überein. Die berechneten Energien der zwei ersten NV-Übergänge: ¹ _g ^{+ 1} _u ^– und ¹ _g ^{+ 1}_u sind: 4,7 und 4,8 eV. Diese Werte sind nicht in Widerspruch mit der Erfahrung, die diese Übergänge über 4,1 eV ansetzt; denn das Stadium der Kometenspektren ist über dieser Grenze wegen der Luftabsorption unmöglich.

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Nous remercions le Professeur P. Swings (Institut d'Astrophysique, Cointe-Sclessin, Belgique) ainsi que le Professeur Ch. Fehrenbach (Observatoire de Marseille), pour les échanges de vue que nous avons eu avec eux sur ce sujet.     

MO LCAO calculations and the electronic spectra of the anions of cyclopent-4-ene-1,3-diones and indane-1,3-diones

The Hückel approximation in MO LCAO is used to show that the anion system of cyclopent-4-ene-1,3-dione should have two ^* transitions: a weak one at long wavelengths, NV₁, and a strong one at short wavelengths, C=C(1,3)V₁. An ethylene, phenyl, or acyl group at position 2 gives rise to a new strong band, NC=C(2), Nbenz, or NC=O (2). A p-nitrophenyl group at position 2 gives rise to a strong NNO₂ band, which overlaps the weak NV₁ band, while the Nbenz band becomes weak and is virtually lost from the spectrum.     

A simplified View of δ → δ* Transition Energies in Compounds with multiple metal-metal bonds: The isolated δ — δ* manifold model

The energetics of the * transition in quadruply bonded complexes are investigated using a very simple valence-bond formalism, called the isolated * manifold (IDDM) model. In this model all electrons except for those that occupy the or * molecular orbitals are ignored, as are explicit metal-ligand interactions. The resulting equations allow the calculation of transition energies very inexpensively, albeit with poor quantitative agreement: the * transition in prototypical quadruple-bond systems is predicted to occur at energies greater than 70,000 cm¹. The model incorporates configuration interaction between the two¹ A _1g configurations (|| and |**|) to roughly the same extent as do correlated all-electron calculations. The application of the method to systems that involve relative changes in * transition energies, such as the torsional twisting of quadruple bonds, is more successful quantitatively.     

X-ray diffraction (powder), e.s.r. and other spectral studies oftris[methylenebis(diphenylphosphine oxide)]iron(III) perchlorate

Summary Bifunctional methylenebis(diphenylphosphine oxide) (mdpo) on reaction with iron(III) perchlorate forms the complex, [Fe(mdpo)₃](ClO₄)₃ · H₂O. This has been characterized through elemental analysis, i.r., far-i.r., u.v. and visible spectroscopy and by x-ray diffraction, magnetic moment, molar conductance and e.s.r. data. The e.s.r. spectrum consists of five lines with transitions from: ¦–5/2¦–3/2¦–3/2¦–1/2, ¦–1/2¦+1/2¦+1/2¦+3/2 and ¦+3/2¦+5/2 centred at a g-value of 2.00. On the basis of these studies, a chelated octahedral structure has been assigned to the cation, [Fe(mdpo)₃]³⁺.     

Zum Mechanismus der Reaktion zwischen Hydrazin und Permanganat

Zusammenfassung Der Mechanismus der Reaktion zwischen Hydrazin und Permanganat wird im Sinne der jüngst dargelegten Chemie des NH₂-Radikals entwickelt. Betätigt sich hierbei Hydrazin in der Tat sowohl reduzierend als oxydierend, so muß es parallel dem Vorgang MnO₄ ^–+N₂H₄Mn²⁺+N₂ zu Zersetzung von Hydrazin im Sinne der Reaktion 3N₂H₄N₂+4NH₃ kommen, die als Manganionkatalyse des Hydrazins anzusprechen wäre. In diesem Fall ist zu erwarten, daß das Aufteilungsverhältnis mit sinkenden Ausgangskonzentrationen sinkt und einem Grenzwert zustrebt. Seinerzeitige Beobachtungen vonCuy, Rosenberg undBray liegen in der Tat in dieser Richtung.     

Triterpene glycosides of Hedera taurica

From the leaves of Crimean ivy we have isolated the previously known glycosides 3-O--L-Ara_p-28-O-[O--L-Rha_p-(14)-O--D-Glc_p-(16)--D-Glc_p]hederagenin, 3-O-[O--L-Rha_p-(12)--L-Ara_p]-28-O-[O--L-Rha_p-(14)-O--D-Glc_p-(16)--D-Glc_p]oleanic acid and -hederagenin, and 3-O-[O--L-Rha_p-(12)--L-Ara_p]-28-O-[O--D-Glc_p-(16)--D-Glc_p]hederagenin and a new one: tauroside H₁ — 3-O-[O--L-Rha_p-(12)-O--L-Ara_p]-28-O-[O--L-Rha_p-(14)-O--D-Glc_p-(16)--D-Glc_p]echinocystic acid.M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 522–528, September–October, 1992.     

Conjugated radicals

Restricted open shell CNDO calculations have been carried out on butadiene anion radical (M_–), butadiene cation radical (M⁺), and butadiene dimer cation radical (M ₂ ⁺ ). Calculated transition energies are in agreement with the experimental data. Formation of M ₂ ⁺ and unsuccessful attempts to detect M ₂ ^– have been interpreted by the CNDO and extended Hückel calculations, in light of which the M + M⁺ M ₂ ⁺ process is energetically favourable while the M + M^– (M ₂ ^– ) process is connected with an energy loss. CNDO calculations support the assumed sandwich structure of M ₂ ⁺ .

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Zusammenfassung Restricted open shell CNDO-Rechnungen für das Butadien-Radikalanion (M^–), das Butadien-Radikalkation (M⁺) und das dimere Butadien-Radikalkation (M ₂ ⁺ ) wurden durchgeführt. Die berechneten Übergangsenergien stimmen mit den experimentellen Daten überein. Die Bildung von M ₂ ⁺ einerseits und die erfolglosen Versuche, das dimere Radikalanion M ₂ ^– herzustellen, andererseits wurden mittels CNDO- und EHT-Berechnungen gedeutet. Es zeigte sich hierbei, daß der Prozeß M + M⁺ M ₂ ⁺ energetisch möglich sein, die Reaktion M + M ₂ ^– M ₂ ^– dagegen mit einem Energieverlust ablaufen sollte. Die CNDO-Rechnungen sprechen für die Annahme einer Sandwich-Struktur von M ₂ ⁺ .

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Résumé On a effectué des calculs avec restricted open shell d'après la méthode CNDO sur l'anion radical du butadiène (M^–) sur le cation radical du butadiene (M⁺) et sur le cation radical du dimère du butadiène (M ₂ ⁺ ). Les énergies de transition calculées sont en accord avec les données expérimentales. La formation de M ₂ ⁺ et les efforts sans succès à prouver la présence de M ₂ ⁺ ont été interprétés par la méthode de CNDO et par les calculs étendus d'après Hückel. De ce point de vue le procès M + M⁺ M ₂ ⁺ est énergétiquement favorable pendant que le procès M + M^– M ₂ ^– est accompagné d'une perte d'énergie. Les calculs d'après la méthode de CNDO soutiennent la structure supposée deM ₂ ⁺ .

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Part XI: ársky, P., Hobza, P., Zahradnik, R.: Collect. Czechoslov. Chem. Commun., in press.     

Proanthocyanidins of Polygonum coriarium. I

Six proanthocyanidins have been isolated from the roots ofPolygonium coriarium. The structures of three oligomeric proanthocyanidins have been established: taranin, consisting of [epigallocatechin gallate]-(48)-[epigallocatechin gallate]-(48)-[epigallocatechin-(48)-epigallocatechin₂-(48)-epigallocatechin; taranoside A - [epigallocatechin gallate]-7-0-[-(16)--D-Glcp]₃-(48)-[epigallocatechin-(48)-epigallocatechin]₂-(48)-gallocatechin; and taranoside B - [epigallocatechin gallate]-7-O-[-(16)--D-Glcp]₄-(48)-[epigallocatechin-(48)-epigallocatechin]₂-(48)-epigallocatechin-(48)-[epigallocatechin gallate).Institute of the Chemistry of Plant Substances, Uzbekistan Republic Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 59–67, January–February, 1992     

Über die Wirkungen von Aldehyden auf gesunde und maligne Zellen, 2. Mitt.: Synthese von homologen 4-Hydroxy-2-alkenalen,I

Zusammenfassung 4-Hydroxy-2-alkenale verschiedener Kettenlänge (C₅–C₁₀) werden in einer mehrstufigen Synthese hergestellt: Alkanal 2-Bromalkanaldimethylacetal 2-Alkenaldimethylacetal 4-Brom-2-alkenaldimethylacetal 4-Hydroxy-2-alkenaldimethylacetal 4-Hydroxy-2-alkenal.     

Kinetic Parameters for Direct Atomic Substitution Reactions

Experimental data (the rate constants and activation energies) for seven reactions of direct substitution of one atom for another D + CH₃R CH₂DR + H, D + NH₃ DNH₂ + H, D + H₂O HOD + H, F + CH₃X CH₃F + X (X = F, Cl, Br, and I) involving atoms D and F and molecules C₂H₆, H₂O, NH₃, CH₃F, CH₃Cl, CH₃Br, and CH₃I are analyzed using the parabolic model of a bimolecular radical reaction. The activation energies for the thermally neutral analogs of these substitution reactions are calculated. Atomic substitution involving deuterium atoms has a lower activation energy of a thermally neutral reaction than radical abstraction or substitution.