Determination of organic carbon in water with a silver-catalyzed peroxydisulfate wet chemical oxidation method

The application of Ag(I) catalysis of S₂O₈^2? to the oxidation of organic carbon to CO₂ for determination of dissolved organic carbon in aqueous samples is described. The resulting method combines to a significant degree the speed of high-temperature combustion methods and the sensitivity of wet chemical oxidation. For some samples, a higher oxidation efficiency has been observed than with an uncatalyzed wet chemical oxidation method.     

Indirect electrochemical methods of nitration: Novel nitroacetamidation of dienes

Solutions of nitronium tetrafluoroborate in acetonitrile prepared by anodic oxidation of nitrogen dioxide, efficiently nitrate aromatics, enolsilyethers, alkenes and conjugated dienes to afford respectively nitroaromatics, α-nitroketones, vicinal nitroamides and mixtures of nitroacetamides by 1,2- and 1,4-addition.     

Monitoring the transformation of colloidal crystals by styrene vapor using atomic force microscopy

The stages of transformation of a colloidal crystalline film of latex spheres to a new periodic structure were imaged by atomic force microscopy. Colloidal crystalline films were prepared with 320 nm diameter poly(styrene-co-2-hydroxyethyl methacrylate) (PSt/HEMA) spheres. The hexagonally ordered surfaces of the colloidal crystalline films were transformed with styrene vapor at room temperature to a new morphology having holes in the surface and the same periodicity as the original films. The surfaces of colloidal crystals and the transformed films have a raspberry-like texture superposed on the 320 nm hexagonal periodicity. Both height images and phase images reveal that the latex spheres shrink and the transformation proceeds by an order-disorder-order sequence. The final structure is an interconnected colloidal array with smaller polystyrene particles dispersed in a continuous PSt/HEMA matrix.     

Peak area measurements of cross-polarization magic-angle-spinning 13C-NMR spectra of crosslinked polystyrenes

Cross-polarization magic-angle-spinning ¹³C-NMR spectra of polystyrenes crosslinked with 1–20% of methine vinyl carbon ¹³C-labeled p-divinylbenzene and of Friedel–Crafts crosslinked poly(chloromethylstyrene)s have been obtained with both glossy solid and CDCl₃-swollen gel samples. The spectra of natural abundance, uncrosslinked, glassy polystyrene, and the spectra of the solid labeled networks give aliphatic and aromatic peak areas only 0.7 times as large per ¹³C atom as that of poly(oxymethylene). Similarly the crosslinked poly(chloromethylstyrene) gave peak areas about 0.6 times that of internal poly(oxymethylene). The labeled gels give peak areas 0.2–0.6 times as large per ¹³C atom as glassy polystyrene, and the peak areas in spectra of gels increase with the divinylbenzene content     

Kinetics of the thermal unimolecular decomposition of hex-1-ene-3-yne. Heat of formation and resonance stabilization energy of the 3-ethenylpropargyl radical

The thermal unimolecular decomposition of hex-1-ene-3-yne (HEY) has been investigated over the temperature range 949–1230 K using the technique of very low-pressure pyrolysis (VLPP). One reaction pathway is the expected C₅? C₆ bond fission to form the resonance-stabilized 3-ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa-1,3-diene. RRKM calculations yield the extrapolated high-pressure rate parameters at 1100 K given by the expressions 10^16.0±0.3 exp(?300.4 ± 12.6 kJ mol^?1/RT) s^?1 for bond fission and 10^13.2+0.4 exp(?247.7 ± 8.4 kJ mol^?1/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and alkadienes. The activation energy for the bond fission reaction leads to ΔH [H₂CCHCC?H₂] = 391.9, DH [H₂CCHCCCH₂? H] = 363.3, and a resonance stabilization energy of 56.9 ± 14.0 kJ mol^?1 for the 3-ethenylpropargyl radical, based on a value of 420.2 kJ mol^?1 for the primary C? H bond dissociation energy in alkanes. Comparison with the revised value of 46.6 kJ mol^?1 for the resonance energy of the unsubstituted propargyl radical indicates that the ethenyl substituent (CH₂?CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc.     

Some reactions of 1-alkyl-1,2,3,4-tetrahydropyridines with organic azides. Synthesis of 1-alkylpiperidylidene-2-sulfonamides

The 1,3-dipolar cycloaddition reaction of 1-substituted-1,2,3,4-tetrahydropyridines 4a-d with organic azides 5 afforded the respective 1-substituted-piperidylidene-2-sulfonamides 6 . In contrast, the reaction of (E)-1-(1-propenyl)-1,2,3,4-tetrahydropyridine ( 4e ) with 4-chlorobenzenesulfonyl azide yielded 6m as well as 1-(4-chlorophenyl)sulfonimine-1,2,3,4-tetrahydropyridine ( 7 ) arising from addition of the azide to the (E)-1-(1-propenyl) substituent of 4e .     

Obtusin,a unique bromine-containing polycyclic ketal from the red marine alga Laurenciaobtusa

The structure of a unique bromine-containing ketal, obtusin ($\text{1}$), has been determined by spectral and X-ray crystallographic techniques. Obtusin is a natural component of the Mediteranean red alga $\text{Laurencia}$$\text{obtusa}$.     

Two-Photon Excitation of 4'-Hydroxymethyl-4,5',8-Trimethylpsoralen

Abstract— Psoralens are a class of pharmaceutical agents commonly used to treat several cutaneous disorders. When irradiated with a mode-locked titanium: sapphire (Ti: sapphire) laser tuned to 730 nm, an aqueous solution of 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) emits blue light. The emission spectrum is centered at 452 nm and is identical to that obtained by one-photon excitation with UVA excitation, and its magnitude depends quad-ratically on the intensity of laser excitation. These results suggest that two-photon excitation occurs to a potentially photochemically active state. To estimate the two-photon absorption cross section, it was first necessary to measure the emission quantum yield of HMT using 365 nm excitation at room temperature that resulted in a value of 0.045 ± 0.007. The two-photon absorption cross section of HMT at 730 nm is therefore estimated to be 20 ± 10⁻⁵⁰ cm⁴ s (20 Göppert-Mayer). The excited-state photophysics and photochemistry of psoralens suggest potential applications to cutaneous phototherapy in diseases such as psoriasis and dystrophic epidermolysis bullosa.     

The number of kekulé structures for rectangle-shaped benzenoids,part VIII: Some perforated rectangles

Summary Classes of coronoids (or degenerate coronoids), r and q are obtained by providing the rectangle-shaped benzenoids R^j (m, 3) with a naphthalenic or pyrenic hole, respectively. The numbers of Kekulé structures (K) are studied. It was found for theK numbers of the classes in question:r=4/5R andq=1/5R. The classes r and q are similar to r and q, respectively, but the naphthalenic or pyrenic hole is oriented in a different way. For these classes it was found:r=3/5R,q=2/5R.

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Die Anzahl von Kekulé-Strukturen für hochkondensierte Benzenoide mit rechteckigem Umriß, 8. Mitt.: Einige perforierte benzenoide Rechteck-Strukturen

Zusammenfassung Es werden Klassen r und q von Coronoiden (oder degenerierten Coronoiden) erhalten, wobei Benzenoide mit rechteckigem Umriß, R^j(m, 3), mit einem Naphthalin- oder Pyren-Loch versehen werden. Die Anzahl von Kekulé-Strukturen (K) wird untersucht; dabei wurde für die untersuchten Klassenr=4/5R undq=1/5R gefunden. Die Klassen r und q verhalten sich ähnlich, das Naphthalin- oder Pyren-Loch ist jedoch anders orientiert; dafür wurder=3/5R undq=2/5R gefunden.