A new analytical method for anchoring quantification of amines on resin support

A rapid and quantitative method for monitoring the efficiency of coupling of amino compounds to polystyrene resin through a carbamate linker has been developed. para-Nitrophenyl carbonate activating group has been shown to release a valuable chromophore for quantitatively monitoring the progress and the yield of the reaction.     

Necessary conditions and duality for inexact nonlinear semi-infinite programming problems

First order necessary conditions and duality results for general inexact nonlinear programming problems formulated in nonreflexive spaces are obtained. The Dubovitskii–Milyutin approach is the main tool used. Particular cases of linear and convex programs are also analyzed and some comments about a comparison of the obtained results with those existing in the literature are given.     

A finitely convergent “row-action” method for the convex feasibility problem

We present a modification of the Cyclic Subgradient Projection (CSP) method by Censor and Lent, which solves the convex feasibility problem in a finite number of steps when a Slater type condition holds, while preserving its row-action properties. A linear rate of convergence for the CSP method is established assuming the same hypothesis.Research partially supported by CNPq, under Grant No. 301699/81.     

Solvent dependence of the 2-naphthyl(carbomethoxy)carbene singlet-triplet energy gap

The solvent dependence of the 2-naphthyl(carbomethoxy)carbene (2) singlet-triplet energy gap has been examined by time-resolved infrared (TRIR) and computational methods. The ground state of 2 changes from the triplet state in hexane to the singlet state in acetonitrile. Preferential stabilization of the singlet carbene is the result of its increased dipole moment in polar solvents. Variable-temperature TRIR experiments provide measurements of the enthalpic and entropic differences between (1)2 and (3)2 and suggest that solvent and geometry effects on the entropy of singlet and triplet carbenes can offset differences arising from spin multiplicity. B3LYP calculations using the polarizable continuum solvation model (PCM) reproduce the general trends in enthalpic differences seen experimentally.     

Semicarbazones and thiosemicarbazones,XII: Crystal structure of salicylaldehyde semicarbazone

Summary The crystal and molecular structure of salicylaldehyde semicarbazone was obtained by single crystal X-ray diffraction. The O atom of the semicarbazone fragment isanti to the N atom of the hydrazinic group. The distribution of bond lengths in the semicarbazone fragment indicates delocalization of the -electrons. The crystal structure is stabilized by intra- and intermolecular hydrogen bonds.

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Semicarbazone und Thiosemicarbazone, 12. Mitt.: Die Kristallstruktur des Salicylaldehyd-Semicarbazons

Zusammenfassung Die Kristallstruktur und die molekulare Struktur des Salicylaldehyd-Semicarbazons wurde über Einkristall-Röntgenstreuung ermittelt. Das O-Atom des Semicarbazonteils stehtanti zum N-Atom der Hydrazin-Gruppierung. Die Bindungslängen in der Semicarbazoneinheit zeigen eine Delokalisierung der -Elektronen an. Die Geometrie der Verbindung wird durch stabilisierende intra- und intermolekulare Wasserstoffbrückenbindungen bestimmt.

     

The mechanism of photoinduced acylation of amines by N-acyl-5,7-dinitroindoline as determined by time-resolved infrared spectroscopy

[reaction: see text] The photochemistry of N-acyl-5,7-dinitroindoline (1) was studied in acetonitrile using nanosecond time-resolved infrared (TRIR) spectroscopy. Upon photolysis, two nearly but not completely overlapping sets of transient IR bands are observed that are assigned to two non-interconvertible conformers of mixed acetic nitronic anhydride 7. While syn-7 reverts rapidly to 1, anti-7 is long-lived and is able to acylate amines. Results of density functional theory calculations support conclusions based on experimental TRIR data.     

Limiting Partial Molar Volumes of Electrolytes in 2-Methyl-2-Butanol <Emphasis Type="Bold">+</Emphasis> Water Mixtures at 298.15 K

Partial molar volumes at infinite dilution, V⁰₂, of alkali–metal halides (LiCl, NaCl KCl RbCl CsCl, NaBr, KBr, KI), tetra-n-alkylammonium bromides, R₄NBr (R=Me, Et, n-Pr, n-Bu, n-Pen), NaBPh₄, and Ph₄PCl have been determined in binary solvent mixtures of water with 2-methyl-2-butanol covering the water-rich region and the alcohol-rich region at 298.15 K. V⁰₂ for alkali–metal halides show relatively little dependence on the solvent composition. However, in the case of hydrophobic electrolytes the observed effects are more pronounced. A good linear dependence between V⁰₂(R₄NBr) and the molecular weight of the tetra-n-alkylammonium cation is found. Limiting single-ion volumes have been obtained using the assumption that V⁰(Ph₄P⁺)–V⁰(BPh^–₄)=2.0 cm³-mol^–1. The trends in the single-ion volumes are discussed in both solvent regions.