The use of Hückel theory charge densities and localization energies for the prediction of kinetic and thermodynamic factors involved in an assumed model for the hydrohalogenation of 1,3-butadiene,isoprene and chloroprene

It is assumed that the first step in the hydrohalogenation of a diene under conditions such that an ionic mechanism is operative involves the formation of a linear carbonium ion via attachment of a proton to the 1-position and that the second step involves addition of the halide ion to either the 2- or 4-positions. If it is also assumed that hyperconjugation plays some non-negligible role in the carbonium ion intermediate, then it turns out that the use of Hückel theory charge densities and localization energies predict (1) that the 1,2-product is kinetically favored in the cases of butadiene and isoprene, (2) that the 1,4-product is kinetically favored in the case of chloroprene, and (3) that the 1,4-product is thermodynamically favored in all of the above systems. All of these predictions appear to be in agreement with available experimental results.

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Zusammenfassung Bei der Addition von Halogenwasserstoffen an die hier untersuchten Diene wird im Reaktions-ablauf ein lineares Carbeniumion angenommen. Das Proton wird in 1-Stellung addiert und in einem zweiten Schritt wird das Halogenion in 2- oder 4-Stellung angelagert. Weiter wird angenommen, daß Hyperkonjugation beim intermediären Carbeniumion eine Rolle spielt. Aus den mit der Hückel-theorie ermittelten Ladungsverteilungen und Lokalisierungsenergien läßt sich dann voraussagen, daß (1) das 1,2-Produkt bei Butadien und Isopren, (2) das 1,4-Produkt bei Chloropren kinetisch und (3) das 1,4-Produkt in allen Fällen thermodynamisch bevorzugt ist. Diese Voraussagen scheinen mit den bekannten experimentellen Resultaten übereinzustimmen.

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Résumé On admet que l'hydrohalogénation d'un diène dans des conditions où prévaut un mécanisme ionique comporte comme première étape la formation d'un ion carbonium linéaire par addition d'un proton à la position 1 et comme seconde étape l'addition de l'ion halogène à l'une des positions 2 ou 4. Si l'on admet par ailleurs que l'hyperconjuguaison joue un rôle non négligeable dans l'intermédiaire carbonium, l'emploi de la théorie de Hückel permet de prédire à l'aide des densités de charge et des énergies de localisation (1) que le produit 1,2 est favorable du point de vue cinétique dans les cas du butadiène et de l'isoprène (2) que le produit 1,4 est favorable du point de vue cinétique dans le cas du chloroprène et (3) que le produit 1,4 est favorable du point de vue thermodynamique dans tous ces systèmes. Toutes ces prédictions sont apparemment en accord avec les résultats expérimentaux disponibles.

     

Zum Nachweis der Oxyde von Molybdän,Wolfram und Vanadin

Zusammenfassung Es wird eine sehr empfindliche Reaktion zum Nachweis der Oxyde des Molybdäns, Wolframs und Vanadins angegeben. Sie beruht auf der Abscheidung von braunem Thallium(III)-oxydhydrat, aus ammoniakalischer Lösung von Thallium(I)-salzen auf Zusatz von Wasserstoffsuperoxyd und den oben genannten Oxyden, die hiebei als Katalysatoren wirken.Herrn Prof. Dr.Emil Abel, dem österreichischen Altmeister der Katalysenforschung, zum 80. Geburtstag.     

Reactions of Hydroxyazolidines with π-Donor Heterocycles. 3. Reaction of 1-Acetyl-5-hydroxypyrazolidines with Oxindoles

The reaction of oxindoles with 5-hydroxypyrazolidines on the surface of potassium fluoride-modified alumina leads to 3-(5-pyrazolidinyl)oxindoles. The structure of these products was studied.     

Structure analytical methods for quantitative reference applications

The analytical methods mass spectrometry, UV/Vis, IR, Raman, Fluorometry, XRD, Mössbauer, and NMR used to elucidate chemical structure are evaluated regarding their capabilities to be used as primary analytical techniques in quantitative measurements, considering the criteria in the CCQM definition of primary methods. This includes a review of the respective measurement equations, the evaluation of the measurement uncertainty, and a discussion of evidence for the “highest metrological level”, as obtained from intercomparisons in contest with other methods. It is shown that only few methods fulfill the CCQM criteria. Quantitative NMR spectroscopy is one of them and may be considered as a potential primary method as recommended by CCQM because of being free of empirical factors in the uncertainty budget.     

Remarkably efficient oxidative coupling of N,N-dialkylarylamines in water mediated by cerium(IV) ammonium nitrate

A highly effective, economical, and environmentally friendly method using of CAN as oxidant and water as solvent for oxidative coupling of N,N-dialkylarylamines was reported.     

High-performance anion-exchange chromatographic study of desialylated human alpha 1-acid glycoprotein variants. Development of a fractionation method for the protein slow variants

The three main desialylated variants (F1, S and A) of human alpha 1-acid glycoprotein (AAG), a serum acute-phase reactant, were analysed by high-performance anion-exchange chromatography in order to determine their optimum separation conditions. The analysis consisted of three steps, as follows: (1) A desialylated commercial AAG was separated into one "fast"- and one "slow"-migrating fraction by preparative isoelectrofocusing. The "fast" and "slow" fractions were shown to contain the F1 variant and a mixture of the S and A variants, respectively. (2) The pH titration curves of these two fractions were then measured by strong anion-exchange chromatography with several buffer systems of increasing pH. From the data obtained, it was not possible to select the optimum conditions to separate the "fast" variant F1 from the "slow" variants A and S. However, the S and A variants were shown to ionize very differently. (3) The specific fractionation of the S and A variants was therefore carried out by anion-exchange chromatography under operating conditions based on the data obtained from the study of their pH titration curves. This was performed both with the "slow"-migrating fraction obtained by preparative isoelectrofocusing of commercial AAG and with an AAG (containing only variants S and A) purified from an individual serum on immobilized Cibacron Blue F3G-A. Identification of the fractionated proteins was achieved by analytical isoelectrofocusing.     

Form of the dihedral angle dependence of the spin-spin coupling constant JHNNH

Cyclic hydrazides (derivatives of phtalhydrazide,pyrozolidone-3, indazolone, cyclic hydrazide camphoric acid) are studied by the NMR¹H method. The size of the dihedral HNNH angle of several model compounds (pyrozolidone-3, cyclic hydrazide norcamphoric acid) are calculated by the MINDO/3 SSF MO LCAO method. It is shown that in the hydrazides with HNNH dihedral angle 0–70° the magnitude of the HNNH spin-spin interaction constant does not exceed 1 Hz. The form of its dependence on the dihedral angle is determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 363–366, 1989.     

Analysis of the globins from fast human haemoglobins by isoelectrofocusing on polyacrylamide gel rods

The globins from all fast haemoglobin (Hb) components obtainable by Bio-Rex 70 cation-exchange chromatography were examined by isoelectrofocusing on polyacrylamide gel rods with 8.0 mol/l urea. From this analysis HbA1a1 and HbA1a2 seem to be very heterogeneous components. HbA1b is separable into two components, one of which is varied in both the beta chains. Between HbA1b2 and the well-known HbA1c components two chromatographic peaks are separated, one with a noticeable percentage of glucosylated beta chain and one that probably contains HbF. HbA1c has both beta chains glucosylated, while HbA1x seems to be a beta monoglucosylated Hb form. Finally, the early part of the HbAo peak has a large amount of glucosylation on both alpha and beta chains.     

Fitting tabulated current functions to linear-sweep voltammograms

A procedure is described for fitting tabulated theoretical current functions to linear-sweep voltammograms. The method, suitable for a small microcomputer, employs linear extrapolation between current function values, and non-linear regression for minimizing deviations between experimental and theoretical currents. Examples of its use for confirmation of simple electrode reaction mechanisms and estimation of electrochemical parameters are described.