Interconversion of the thiazine and thiazolidine system of β-lactam antibiotics,electrochemical cleavage of kamiya's disulphide promoted by bromide ion

A new transformation of Kamiya's disulphide ($\text{1}$) into the bromopenam derivative ($\text{4}$) has been carried out by electrolyzing the disulphide ($\text{1}$) in protic solvents in the presence of Me₄NBr. The transformation occurs through an intermediate episulphonium-bromide ion pair in which the bromide appears to tightly linked to the sulphur.     

Binding of gaseous Fe(III)-heme cation to model biological molecules: Direct association and ligand transfer reactions

The binding of a variety of ligands with Fe(III)-heme(+) ion, prosthetic group of heme proteins, has been studied in the gas phase by ESI-FT-ICR mass spectrometry. The ligands have been selected among substrate molecules of heme proteins (e.g., NO, nitroso compounds) or among model compounds acting for the functional groups that are present in the protein backbone (e.g., amines, thioethers, nitriles, ketones, amides, etc.). Both the kinetic and the thermodynamic features of the addition reactions are reported. Fe(III)-heme(+) ions react faster with lone pair donor ligands as the reaction becomes increasingly thermodynamically favored (higher heme cation basicity of the ligand, HCB, namely -DeltaG degrees for the ligand addition reaction). In turn HCBs correlate in general with the gas phase basicity toward the proton of the various ligands. A ligand addition equilibrium is established with weaker ligands, methanol, acetonitrile and acetone, yielding absolute HCB values, whereas ligand transfer equilibriums allowed a scale of relative (and absolute) HCBs to be constructed. NO displays exceptional binding properties towards Fe(III)-heme(+), unrelated to the low gas phase basicity toward the proton of this molecule, which is clearly the basis for the paramount role of heme proteins in NO binding and regulation.     

A reusable, insoluble polymer-bound bis(oxazoline) (IPB-box) for highly enantioselective heterogeneous cyclopropanation reactions

A reusable, insoluble polystyrene-supported bis(oxazoline) was developed, affording e.e.s > 90% in the heterogeneous enantioselective cyclopropanation of styrene and 1,1-disubstituted alkenes with ethyl diazoacetate.     

Valence bond treatment of systems involving orbital degeneracy

A semiempirical valence-bond treatment including polar structures has been developed. Explicit formulas are given for the calculation of energy matrix elements and of charge and spin densities. The method has been applied to benzyl and allyl radicals and to butadiene.

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Zusammenfassung Es wurde ein semiempirisches Valence-Bond-Verfahren einschlie\lich Polar-Strukturen ent-wickelt. Explizite Formeln werden für die Berechnung von Energiematrixelementen und für die Ladungs- und Spin-Dichte angegeben. Die Methode wurde auf das Benzyl- und das Allyl-Radikal und auf Butadien angewendet.

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Résumé On a dévelopé un traitment semi-empirique de la méthode des orbitals de valence avec inclusion des structures polaires. On donne des formules explicitées pour le calcul des éléments matriciels de l'énergie et des densités de charge et de spin. On a appliqué la méthode aux radicaux benzylique et allylique et à la molecule du butadiène.

     

Valence bond treatment of systems involving orbital degeneracy

Ground and excited electronic states of the allyl cation and anion, the butadiene radical cation and anion, and of the pentadienyl cation and anion have been calculated by a semiempirical valence bond method. The results of such calculations are in essential agreement with the known properties of such systems. A comparison of the results of the valence bond treatment with those expected on the basis of the qualitative resonance theory yields serious discrepancies which show up the limitations inherent in the latter formalism.

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Zusammenfassung Der Grundzustand und die elektronisch angeregten Zustände der folgenden Systeme wurden mittels einer semiempirischen Valence-Bond-Methode berechnet: Allyl Kation und Anion, Butadien Radikal Kation und Anion, Pentadienyl Kation und Anion. Die Ergebnisse stehen in vernünftiger Übereinstimmung mit den bekannten experimentellen Daten. Ein Vergleich der Resultate, die mittels der Valence-Bond-Methode erhalten werden, mit jenen, die man aufgrund der qualitativen Resonanz-Theorie erwarten würde, ergibt wesentliche Unterschiede, die auf die Grenzen hinweisen, die dem letztgenannten Formalismus eigen sind.

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Résumé L'état fondamental et les états électroniques excités du cation et de l'anion allyl, du cation radical et de l'anion radical du butadiène et du cation et de l'anion pentadiényl ont été calculés par la méthode semiempirique valence bond. Les résultats de ces calculs correspondent raisonnablement aux données expérimentales connues pour ces systèmes. Une comparaison des résultats théoriques avec les prédictions de la théorie de résonance donne des différences qui démontrent les limites de ce formalisme qualitatif.

     

The orthogonality problem in valence bond calculations

The energy of the π-electron system in benzene has been obtained by means of valence bond calculations using orthogonal and nonorthogonal basis orbitals at different levels of configuration interaction, which shows the influence of the orthogonalization procedures.     

Ab initio valence bond calculations. VII. HF,HF+, and H2F+

Ab initio valence bond calculations for the ground and excited states of HF and HF⁺ are presented. Total energies, equilibrium geometries, dissociation energies, dipole moments, and spectroscopic constants for HF and HF⁺ have been calculated. The photoelectron spectrum of HF has been examined and interpreted by means of the valence bond formalism. The ground state of the protonated species H₂F⁺ has been investigated.     

Interpretation of electronic spectra of aromatic hydrocarbons by the “molecules in molecules” method

The molecules in molecules method has been applied to five groups of hydrocarbon molecules or ions. Energy, polarisation and intensity of electronic transitions have been compared with experimental data and previous theoretical results. The results show that the method is applicable even when there is relevant conjugation between the fragments.

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Zusammenfassung Die molecules in molecules-Methode wurde auf fünf Gruppen von Kohlenwasserstoff-Molekülen angewandt. Energie, Polarisation und Intensität von elektronischen Übergängen wurden mit experimentellen und theoretischen Resultaten verglichen. Die Resultate beweisen, daß die Methode anwendbar ist, auch wenn eine wesentliche Konjugation zwischen den Fragmenten besteht.

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Resumé La méthode molecules in molecules a té appliquée à cinq groupes de molécules ou ions d'hydrocarbures. On a comparé les energies, la polarisation et l'intensité des transitions électroniques avec les données experimentales et les données théoriques qu'on avait précedemment calculées. Les résultats indiquent que la méthode est appliquable, même lorsqu'on a une conjugation assez importante entre les fragments.