The correlation of NMR chemical shifts with EHT calculated electron densities for 3-pyridinols

The NMR spectra of a series of five 3-pyridinols in dioxane and dimethyl sulfoxide have been correlated with electron densities calculated by the Extended Hückel MO method. The data were found to fit a straight line of the form y=ax+b. The effects of hydrogen-bonding between pyridinol molecules on the correlation have been considered, and they have been estimated quantitatively for 6-methyl-3-pyridinol via Extended Hückel Calculations on a hydrogen-bonded model.

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Zusammenfassung Die Kernresonanzspektren von fünf 3-Pyridinolen in Dioxan und Dimethylsulfoxyd wurden mit den Elektronendichten aus dem erweiterten Hückelverfahren korreliert, und zwar ergibt sich eine lineare Beziehung. Der Einfluß von intermolekularen Wasserstoffbrücken ist für einen Fall (die 6-Methyl-Verbindung) durch EHT-Rechnungen festgestellt und in den übrigen Fällen geschätzt worden.

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Résumé Les spectres NMR d'une série de cinq 3-pyridinols dans le dioxane et le diméthyle-sulfoxyde ont été corrélés avec les densités électroniques calculées par la méthode de Hückel Etendue. Les données se placent correctement sur une droite y=ax+b. Les effets de la liaison hydrogène entre les molécules de pyridinol ont été envisagés et estimés quantitativement pour le 6-méthyl-3-pyridinol par des calculs EHT sur un modèle à liaison hydrogène.

     

The electronic structure of molecules by a many-body approach : II. Ionization potentials one-electron properties of pyridine and phosphoridine

The valence ionization potential (IPs) of pyridine and phosphoridine are studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the Hartree-Fock approximation. For pyridine the order of the first three IPs is a₂(π), a₁(n), b₁(π), but the IPs of the a₂ and a₁ orbitals are so close together that they have to be regarded as identical in binding energy, which is also concluded from experiment. Whereas for pyridine the ordering of the IPs calculated in the HF approximation is incorrect, it is correct for phosphoridine. For this latter molecule the first three ionization potentials are due to ionization from the b₁(π), a₂(π), and a₁(n) orbitals. Several one-electron properties are calculated and compared with experimental and other theoretical data. The localized molecular orbitals are discussed as well.     

Long-range interaction between 1s and 2s or 2p hydrogen atoms

Long-range interaction energy between two hydrogen atoms has been computed in the second order of the perturbation theory. All states of the system arising when one of the atoms is in the 1s and the other in the 2s or 2p state have been considered. The energy represented by a series expansion in inverse powers of the internuclear distance, R, has been computed up to the terms in R^?8. The results are believed to give reliable interaction energies for R > 15 a.u. Accurate interaction energy for two ground-state hydrogen atoms has also been obtained up to the terms in R^?10. Results for the B′ ¹∑ state are employed to discuss the experimental ground-state dissociation energy of H₂, D₂, and HD. For H₂ all values of the dissociation energy obtained from various experimental absorption limits, by using the computed potential energy curve to separate off the effect of rotation, are shown to be satisfactorily consistent. The resulting total energy of H₂ is, however, higher than the most accurate theoretical value.     

A simple technetium generator

A systematic study on the extraction of⁹⁹Mo and its daughter^99mTc by pure organic diluents and dinonylnaphthalinesulfonic acid (DNNS) is described. The aqueous phases used are H₂SO₄, HCl, KI and their binary mixture solutions. The effect of alcohols on the distribution coefficient has been investigated. As a result of the study, a simple and rapid generator is built for the production of pure^99mTc from⁹⁹Mo.     

13C Chemical shifts of some azaindolizines versus electron charge distribution

Azaindolizines, which contain all possible combinations of nitrogen atoms within the five-membered ring moiety, are used as models for the investigation of a relationship between electron charge distribution and ¹³C shifts. A linear correlation is observed between the shifts and total rather than π-charge densities as calculated by the INDO-MO method. The average excitation energy (AEE) approximation in the theory of nuclear screening is shown to hold separately for the CH moieties and the carbon atoms at the ring junction in indolizines. An empirical correlation with charge densities is obtained from the AEE method, as a result of the compensation of effects within the local paramagnetic term and the prevailing contribution to the latter of the effective nuclear charge.¹³C shifts afford a reasonable measure of the total net charges at the carbon atoms of indolizines. The INDO calculations indicate that the π-charges follow the pattern suggested by simple resonance structures but the overall charge density depends heavily on σ-core polarization effects.     

Exchange reactions between oxygen and sulphur derivatives of silicon, germanium, tin and lead

The exchange of oxygen functional groups (--- OR, --- O --- and --- OCOMe) and sulphur functional groups (--- SR, --- S --- ) between R₃M (M = Si, Ge, Sn and Pb) and R₂M (M = Si, Sn) shows, in general, the heavier Group IV element to prefer sulphur. This supports the phenomenological rationalisation that the softness of the organometallic residue increase with the atomic weight of M, though germanium probably resembles silicon in its behaviour far more that it does tin.     

Lumineszenzspektren von ein- und zweikernigen Chrom(III)-Glycin-Komplexverbindungen

The luminescence spectra of the polycrystalline compounds [Cr(CH₂NH₂COO)₃ · H₂O] and [Cr₂(OH)₂(CH₂NH₂COO)₄] are investigated in the temperature range of 120K – 4.2K. From the known crystal structure (P2_1/c =D _2h ^/5 ) of the mononuclear compound assignment of the zero-phonon bands based on crystal field theory becomes possible. Both of the highly intense phosphorescence transitions are observed at \(P_1 = 14493 cm^{ - 1} ({}^2A'' \xrightarrow{{0.0}} {}^4A) and P_2 = 14428 cm^{ - 1} ({}^2A' \xrightarrow{{0.0}} {}^4A)\) . Assignment of the accompanying vibronic bands is made from the measured infrared data. Crystal field parameters Dq, B and C are determined from the luminescence and reflectance spectra. In the case of the binuclear compound the Cr³⁺-Cr³⁺ interaction via hydroxyl brides may be described by an axchange operator \(H_{ex} = - 2 \sum\limits_{ij} {J_{ij} S_i^a \cdot S_j^a } \) and from this the energy level diagram is calculated. Both observed strong phosphorescence bands at 14369 cm^?1 and 14184 cm^?1 are assigned to \(\left| {{}^2E \cdot {}^4A_2 \rangle _{s = 2} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 2} and \left| {{}^2E \cdot {}^4A_2 \rangle _{s = 1} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 1} \) transitions.     

High-resolution small-angle x-ray investigations on poly-o-bromostyrene in benzene solutions

Small-angle x-ray investigations on poly-o-bromostyrene in benzene solution at extremely high resolution (corresponding to a Bragg's value of 3200 Å) proved to be able to link together the ranges covered by small-angle x-ray scattering and light scattering. On the other hand, there are problems encountered in molecular weight determination of chain molecules, since both methods at extremely small angles and at finite concentrations reach the limits of particle scattering. The differing results obtained by means of the two methods for the molecular weight of a rather high molecular weight sample of poly-o-bromostyrene are ascribed to entangelements stabilized by dipole–dipole interactions. These, due to the differing Bragg's angles and concentration ranges in the two methods, affect the experimental results to a different degree.     

Zur hochspannungselektrophoretischen Trennung anorganischer Ionen unter besonderer Berücksichtigung der Platmmetalle

Zusammenfassung Die hochspannungselektrophoretische Wanderung der Halogenokomplexe der Platinmetalle und einer Reihe weiterer anorganischer Ionen wird mit Nitrilotriessigsäure und Äthylendiamintetraessigsäure als Elektrolyt in Abhängigkeit von verschiedenen Versuchsparametern (Elektrolytkonzentration,ph-Wert und Substanzmenge) untersucht. Die Wanderungsgeschwindigkeiten der verschiedenen Metallionen bzw.-komplexe zeigen charakteristische Abstufungen, die sich mit den für die hochspannungselektrophoretische Wanderung gültigen Gesetzmäßigkeiten erklären lassen. Beispielsweise beobachtet man eine Abnahme der Beweglichkeit bei Ersatz von Chlorid- durch Bromidionen (Masseneinfluß), Auswirkungen der vomph bzw. der Elektrolytkonzentration abhängigen unterschiedlichen Komplexierungen zwei- und dreiwertiger Ionen, Einflüsse der auf Hydrolyse zurückgehenden Änderungen der Ligandenzusammensetzung sowie Unterschiede der Wanderungsgeschwindigkeiten als Folge der Komplexierung mit NTE oder AeDTE.Durch die unter bestimmten Bedingungen erreichbare Abstufung der Beweglichkeiten können verschiedene Gemische, unter anderem auch die Chlorokomplexe der meisten Platinmetalle in der Reihenfolge Ir > Os Pt > Rh Pd > Ru (> Rh), getrennt werden. NTE ist dabei für Trennungen besser als AeDTE geeignet.

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The high tension electrophoretic separation of inorganic ions with special reference to the platinum metals. I

Summary The high tension electrophoretic migration of the halogeno complexes of the platinum metals and several other inorganic ions was investigated with nitrilotriacetic acid and ethylenediaminetetraacetic acid as electrolytes in relation to the various experimental parameters (electrolyte concentration,ph-value, and amount of substance). The migration velocities of the various metal ions or complexes exhibit characteristic gradations that may be explained on the basis of the regularities that are valid for the high tension electrophoretic migration. Instances are: a decrease was observed in the mobility when chloride was replaced by bromide ions (mass effect), influence of different complexing of di- and trivalent ions that are related to changes in theph or electrolyte concentration, or influences of the changes due to hydrolysis in the composition of the ligands or alterations in the migration rates resulting from complexing with nitrolotriacetic acid or EDTA.The gradation of the mobility obtained under certain conditions are employed as the basis of a procedure for separating various mixtures, including also the chloro complexes of most of the platinum metals in the succession Ir > Os Pt > Rh Pd > Ru (> Rh). It has been found that NTE is better for separations than EDTA.

     

Boron-boron bonding in pentaborane-9

Calculations of the electronic structure of pentaborane-9 have been carried out using MO, VB, three-centre bond, and NPSO wavefunctions, in order to determine the approximation most suitable for this type of molecule. The best of these wavefunctions as determined by comparison with a tenparameter CI function, was one of the NPSO functions.

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Zusammenfassung Die Elektronenstruktur von Pentaboran-9 wurde unter Verwendung von MO-, VB-, NPSO- und Dreizentrenbindungs-Wellenfunktionen berechnet. Die am besten geeignete unter diesen ist nach einem Vergleich mit einer zehnparametrigen CI-Funktion die NPSO-Funktion.

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Résumé Des calculs de la structure électronique du 9-pentaborane ont été effectués en utilisant des fonctions d'onde M.O., V.B., liaisons à trois centres et NPSO, afin de déterminer l'approximation qui convient le mieux à ce genre de molécule. La meilleure de ces fonctions d'onde, en comparaison d'une fonction d'I.C. à dix paramètres, s'avère l'une des fonctions NPSO.