Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical onto Cyclic Alkenes in Solution

Absolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical ^.CHMeCO₂(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain.     

Lattice Thermal Transport in the Homogeneous Cage-Like Compounds Cu3VSe4 and Cu3NbSe4: Interplay between Phonon-Phase Space,Anharmonicity, and Atomic Mass

Understanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat-transport-related devices, such as high-performance thermoelectric materials and heat dissipation in micro-nano-scale devices. In this work, the lattice thermal conductivity ( ) of the cage-like compounds Cu₃VSe₄ and Cu₃NbSe₄ was investigated by experimental measurements and first-principles calculations. The experimental of Cu₃NbSe₄ is approximately 25 % lower than that of Cu₃VSe₄ at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third-order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the , and the other factors only play a minor role. The physical origin is the relatively “soft” lattice of Cu₃NbSe₄ with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high-performance thermal management device and thermoelectric materials with intrinsically low .     

Solubility of carbazole in binary chloroalkane + dibutyl ether solvent mixtures

Solubilities are reported for carbazole in three binary chloroalkane + dibutyl ether solvent mixtures at 25°C. Results of these measurements are compared with solution models developed for solubility in systems containing specific solute-solvent interactions. A simple model based on a single 1:1 carbazole:dibutyl ether complex described the solubility data, though the calculated equilibrium constant was about one-half of values published previously. A more sophisticated solution model, which assumes both carbazole:dibutyl ether and carbazole:chloroalkane complexes, was needed to thermodynamically describe the systems studied. Equilibrium constants for three presumed carbazole:chloroalkane complexes are calculated from measured carbazole solubilities.     

Measurement of the sign and the magnitude of heteronuclear coupling constants from spin-state-edited J-cross-polarization NMR experiments

New spin-state-selective (S3) NMR pulse sequences exclusively applying cross-polarization schemes to achieve optimum homonuclear and heteronuclear 1H-X coherence transfer are reported for the simple and accurate measurement of the magnitude and sign of heteronuclear coupling constants for samples at natural abundance. The proposed spin-edited HCP-TOCSY experiments are based on clean heteronuclear S3 excitation, generated by simultaneous co-addition of two independent in-phase and anti-phase components created during the mixing heteronuclear J-cross-polarization (HCP) step, which is finally transferred to other protons by a conventional homonuclear TOCSY mechanism. Selective 1D and non-selective 2D approaches for the easy determination of long-range proton-carbon and proton-nitrogen coupling constants on any protonated and non-protonated heteronuclei are presented and discussed for several organic molecules.     

Sorption of aliphatic ketones from aqueous solutions by starch cryotextures

Capillary gas chromatography was applied to study the sorption of aliphatic ketones (C₆—C₁₁), including metamers, from aqueous solutions by corn starch cryotextures. The amount of ketones sorbed by cryotextures depends linearly on their concentrations in the initial sol. Equations describing the concentration dependence of sorption were proposed. The shape of sorption isotherms reflects the strength of sorption. The binding constants and the number of binding sites were determined for weakly sorbed ketones. The length of alkyl substituent and the position of the functional group are the crucial factors governing the sorption of ketones under conditions of excess binding sites. It was found that the degree of sorption increases with an increase in the carbon chain length from 6 to 9 carbon atoms. The presence of cooperation of binding sites for ketone sorption by cryotextures was demonstrated. The major part of ketones is sorbed irreversibly. This fact points to the formation of supramolecular complexes. Ketones with lower molecular masses are better sorbed by cryotextures than by native starch grains.     

Tetraarylester der μ-Imidodiphosphorsäure und ihre Thioderivate — Strukturuntersuchungen

Tetraarylesters of μ-Imido-Diphosphoric Acid and its Thio Derivatives — Structure Investigations New O,O′,O″,O?-tetratolyl- and ditolyl-diphenylesters of the μ-imido-diphosphoric acid and its mono and dithio derivatives were synthesized, compared with the corresponding tetraphenylesters and investigated by ¹H, ¹³C, and ³¹P NMR spectroscopy and X-ray crystal structure analysis. Structures of the O,O′,O″,O?-tetrakis-(2-methyl-phenyl)-μ-imidodiphosphate, 1b , as well as of the corresponding ortho-, meta- and para-tolylesters of the μ-imido-monothiodiphosphoric acid ( 2a , 2b , 2c ) were determined. All the compounds form dimers via N? H…?O hydrogen bonds in the crystal as well as in nonpolar solvents. The distances around the phosphorus atoms rise with decreasing electronegativity of the phosphorus substituents. Signs of the ²J_{P? N? P} coupling constants were determined by ¹³C{¹H, ³¹P} triple resonance experiments for some compounds. These constants become more negative owing to substitution of a phosphoryl by a thiophosphoryl group.     

Determination of the micelle-solute association constants of some benzene and naphthalene derivatives by micellar high performance liquid chromatograph

Summary The interaction of some benzene and naphthalene derivatives with sodium dodecyl sulphate, hexadecyltrimethylmmonium bromide and polyoxyethylene [23] dodecanol micelles has been evaluated by high operformance liquid chromatography using micellar mobile phases. The micelle-solute association constants have been obtained for the compounds investigated. Good correlation between free energy of transfer for water-micelles and for octanol-water has been observed.     

Structure inhomogeneities of medium-range order in fluorozirconate glasses

Images of cleaved surfaces were obtained for 53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å.     

Basicity of 4-aminopyrimidine and 2,4-diaminopyrimidine derivatives

Summary The basic dissociation constants for a series of 30 4-aminopyrimidine and 2,4-diaminopyrimidine derivatives were determined in 2% v/v aqueous methanol by a spectrophotometric method. The determinedpK _a values correlate well withHammet's constants.

---

Basizität von 4-Aminopyrimidin- und 2,4-Diaminopyrimidinderivaten

Zusammenfassung Die basischen Dissoziationskonstanten einer Reihe von 30 4-Aminopyrimidin-and 2,4-Diaminopyrimidinderivaten wurden in 2% v/v wäßrigem Methanol durch spektroskopische Methoden bestimmt. Die ermitteltenpK _a-Werte korrelieren gut mit den entsprechendenHammett-Parametern .