Cathode-catalyzed transesterification of alkylphosphonates

The cathodic electrolysis of aliphatic alcohols and alkylphosphonates in acetonitrile with 0.5 N Et₄NClO₄ as the base electrolyte leads to mono- and ditransesterified phosphonates. The yield and ratio of these products is a function of the nature of the starting reagents and amount of current passed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 200–204, January, 1991.     

Investigations on surface diffusion in sparingly soluble monolayers at the gas/liquid interface using radiotracer technique

Summary A method is proposed for calculating surface selfdiffusion coefficients in sparingly soluble monolayers at fluid interfaces based on radiotracer measurements and allowing for counter geometry. On this basis an analysis of experimental results is possible without having to allow for processes competing with surface self-diffusion. Monolayers of various long-chainn-alcohols andn-alkane-carboxylic acids were studied in the area range between 0.23 nm²/molecule and 2.0 nm²/molecule. Surface self-diffusion coefficientsD _s were determinded only up to areas of 0.75 nm2/molecule since, in case of greater areas, the analysis of surface concentration becomes inexact due to the increasing influence of density convection. For the systems studied,D _s values lie in the order of 10^–5 cm²/s. In all compounds studied, the values ofD _s increase with area per molecule. In addition, dependence on the type of hydrophilic group and alkyl-chain length of monolayer molecules was proved. The results are discussed by means of various model concepts.

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Zusammenfassung Ein Verfahren zur Berechnung der Oberflächenselbstdiffusionskoeffizienten in schwerlöslichere Monoschichten an fluiden Phasengrenzen auf der Grundlage von Radiotracermessungen und unter Berücksichtigung der Zählrohrgeometrie wird vorgeschlagen. Auf dieser Basis ist eine Auswertung der Experimentalergebnisse möglich, ohne daß zur Oberflächenselbstdiffusion in Konkurrenz stehende Transportvorgänge berücksichtigt werden müssen. Untersucht wurden Monoschichten verschiedener längerkettigern-Alkanole undn-Alkancarbonsäuren im Flächenbereich zwischen 0,23 nm²/Molekül und 2 nm²/Molekül. OberflächenselbstdiffusionskoeffizientenD _s wurden nur bis zu Flächenwerten von 0,75 nm²/Molekül bestimmt, weil bei höheren Flächen die Auswertung der Oberflächenkonzentrationsänderungen wegen des zunehmenden Einflusses von Dichtekonvektion ungenau wird. DieD _s -Werte liegen für die untersuchten Systeme in der Größenordnung 10^–5 cm2/s. Bei allen untersuchten Verbindungen nehmen die Werte von D_s mit steigender Fläche pro Molekül zu. Außerdem wurde die Abhängigkeit von der Art der hydrophilen Gruppe und der Alkylkettenlänge der Monoschichtmoleküle nachgewiesen. Die Ergebnisse wurden anhand verschiedener Modellvorstellungen diskutiert.

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With 8 figures and 1 table     

The particle structure ofv-dimensional Ising models at low temperatures

In this work we study thev-dimensional Ising model at low temperatures and establish the existence of an upper gap in the energy-momentum spectrum of the two-point function forv3. Forv=2, it is known that this gap is absent.Supported in part by Conselho Nacional de Pesquisas (CNPq-Brazil), Universidade Federal de Minas Gerais (Brazil) and the National Science Foundation under Grant PHY76-17191     

Forbidden matrix proton spin flip satellites in trapped electron EPR spectra

Observation of the 35 GHz EPR spectrum of γ-irradiated 10 M NaOH/H₂O and 10 M NaOD/D₂O glassy ices at 77°K has revealed proton spin flip satellites associated with the trapped elctron EPR line. This suggests that forbidden satellite transitions contribute to the lineshape of the trapped electron line in the 9 GHz spectrum which has commonly been studied.     

A computational study of bond dissociation enthalpies in haloethenes

Carbon–hydrogen bond dissociation enthalpies (BDEs) were computed for all haloethenes, C₂H_4−nX_n (n=0–3, X=F, Cl, Br, I), at the B3LYP/6-311+G(3df,2p) level using isodesmic reactions. It was found that C–H bond strengths in the monohaloethenes varied substantially, by as much as 18 kJ mol⁻¹, dependent upon the bond's stereochemical position relative to the halogen. BDEs in the dihaloethanes varied in the order CX₂CH–H>(E)-CHXCX–H>(Z)-CHXCX–H. Trends in the computed bond enthalpies were discussed and explained on the basis of relative steric repulsions and hyperconjugative delocalization interactions, as determined from Natural Bond Orbital analysis.     

Quantitative NMR measurements in copolymers of vinylidene chloride and acrylonitrile: The effect of saturation and varying nuclear Overhauser enhancements

Spin-lattice relaxation times and nuclear Overhauser enhancements (NOE) for ¹³C nuclei in copolymers of acrylonitrile and vinylidene chloride were measured at 20.1 and 67.9 MHz. In the ? CCl₂? region of the spectrum T₁ and NOE values of the various resonances are equal within experimental error and are invariant to changes in composition. The T₁ and NOE values of the ? CCl₂? region, however, are not equal to those of the ? CH? or ? CN region. As a result compositions cannot be calculated by direct comparison of the areas in the ? CCl₂? region and either the ? CH? or the ? CN region. Discrepancies can be corrected for the ? CH? resonances by multiplication of the area by an empirical constant. A similar constant for the ? CN region is composition-dependent at 20.1 and 67.9 MHz. A chemical shift anisotropy mechanism is postulated as important for relaxation of the ? CN resonances. The overall influence of variable T₁ and NOE values on quantitative determination of polymer composition is considered.     

Complexes of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with chloride,nitrate, iodate,and sulfate ions in aqueous media: I. Formation constants,thermodynamic properties,and bonding mechanisms

Complexation stoichiometries and formation constants of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with NO ₃ ^– , Cl^–, IO ₃ ^– and SO ₄ ^2– ions are determined by pH potentiometric and¹³C NMR spectrometric measurements. Estimates of H and S are obtained from the values of the temperature dependent formation constants and acid dissociation constants. All four anions form only 1 : 1 complexes with the triprotonated amine species. NO ₃ ^– and Cl^– form 1 : 1 complexes only with the tetraprotonated amine, while IO ₃ ^– and SO ₄ ^2– form both 1 : 1 and 2 : 1 complexes. The complexation behavior is interpreted in terms of solvation and internal hydrogen bonding interactions.