Long chain alkyl-polysiloxanes as non-polar stationary phases in capillary gas chromatography

Summary A new methyl-octadecyl polysiloxane phase with a distinct selectivity in PCB separation and a significantly improved temperature range has been developed. The basic structural element of the separation of PCBs on methyl-octadecyl-polysiloxane is the elution according to the number of the substituents in the ortho-positions 2,2 and 6,6. The 2,2,6,6-substituted congeners are eluted first, while the non-2,2,6,6-substituted coplanar PCB are eluted last. As compared to methyl-phenyl (5%) polysiloxane (SE 54) the standard stationary phase used for the separation of the PCBs, the methyl-octadecyl-polysiloxane has several unique features in an improved PCB separation. The Sil 5–50% C18 column resolves the pair PCB 31/28 and also the sets PCB 5/8, PCB 16/15/32, PCB 25/53, PCB 48/47, PCB 56/60, PCB 118/149, PCB 105, 132, 153, and PCB 170/190. All these separations are not achieved with a SE 54 column. No separation is observed for the pair PCB 138/163 on Sil 5–50% C18. The order of elution of the Cl_xB congeners reveals a rather stringent structure correlation. If the structure/retention correlation is extended to all 209 Cl_xB congeners, 20 groups with one ring fixed / one ring variable substitution can be distinguished.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthday.Presented at 14th International Symposium on Capillary Chromatography, May 25–29, Baltimore, USA.     

Levels of polychlorinated biphenyls in the lower troposphere of the North- and South-Atlantic Ocean

Summary Fourteen polychlorinated biphenyl (PCB) congeners were quantified in air samples of the tropospheric boundary layer of the Atlantic Ocean. The samples were taken on the German research vessel Polarstern during north-south cruises across the Atlantic Ocean (1990, 1991), and on the Capo Verde islands in the North Atlantic Ocean (1992). Values for the sum of PCB were between 48 pg/m³ (values for the seven indicator congeners were [in pg/m³]: PCB 28: 1.3; PCB 52: 5.0; PCB 101: 3.0; PCB 118: 0.5; PCB 138: 1; PCB 153: 1; PCB 180: <0.2) in the Westwind Belt of the eastern North Atlantic and 22 pg/m³ (values for the seven indicator congeners were [in pg/m³]: PCB 28: 2.3; PCB 52: 3.4; PCB 101: 0.5; PCB 118: <0.2; PCB 138: <0.2; PCB 153: <0.2; PCB 180: <0.2) in the Westwind Belt of the central South Atlantic. Up to 385 pg/m³ (values for the seven indicator congeners were [in pg/m³]: PCB 28: 2.6; PCB 52: 11.7; PCB 101: 28.4; PCB 118: 9; PCB 138: 21; PCB 153: 18; PCB 180: 5.5) were measured of the coast of South Patagonia. A difference depending on latitude and on terrestrial influenced air masses between the lower and the higher chlorinated congeners was observed. The levels of three- and tetrachlorinated congeners were highest in the Trade Wind regions. The contents of the higher chlorinated congeners had maxima in samples influenced by continental air masses. A correlation of the levels of the lower chlorinated congeners in air over the South Atlantic with the surface water temperature and thus with the temperature dependent gas/water partition coefficient K_gw was observed. Part XVI: Fischer RC, Krämer W, Ballschmiter K (1991) Chemosphere 23:889–900     

Heterocyclic Spiro-naphthalenones. Part II. Synthesis and reactions of some spiro [tetrahydrofuran-2,1′-(2′H-naphthalene)]-2′,5-diones and Spiro [tetrahydrofuran-2,2′-(1′H-naphthalene)]-1′,5-diones

The spiro-lactone 3 was obtained by N-bromosuccinimide (NBS) oxidation of the carboxylate 2 at ? 20°. When 2 was oxidized at 10° the spiro-lactone 4 was the main product. Compound 4 was rearranged with triethylamine to the spiro-lactone 9 whereas the stereoisomeric spiro-lactones 14 and 15 were obtained by NBS oxidation of the carboxylate 13 . The ketones 3, 4, 9, 14 and 15 were reduced with NaBH₄ to the corresponding alcohols 5, 6, 10, 16 and 18 respectively; these were hydrogenated to the alcohols 7, 8, 11 and 20 . The allylic alcohols 5 and 6 gave the benzochromanone 1 when heated in polyphosphoric acid whereas the benzochromanones 12 and 21 were obtained from the alcohols 10 and 16 respectively.     

Reaction Rates of t-Butyl and Pivaloyl Radicals in Solution

The rate constants of the unimolecular decomposition of the pivaloyl radical (k_D) and of the bimolecular self terminations of pivaloyl (k₁) and t-butyl radicals (k₂) in liquid methylcyclopentane are determined by ESR.-spectroscopy: The viscosity dependence of (k₂) is analysed with respect to diffusion control of the reaction. Comparison of (k_D) values of different acyl radicals reveals a strong dependence of the activation energies on radical structure.     

High spin states in77Se populated by the74Ge(α,n γ) reaction

⁷⁷Se has been investigated by the reaction⁷⁴Ge(,n) at 14 MeV. Gamma singles spectra, gamma angular distributions and gamma-gamma coincidences have been taken. A level scheme has been established, spins and parities have been assigned. States of a rotational band on the 1/2^– ground state, a rotational band on the 5/2^– 249.7 keV state and an anormal band have been identified. Nuclear Reaction ⁷⁴Ge(,n )E =14 MeV; measuredE ,I ,--Coin.,-ang. distr.⁷⁷Se deduced levels,J, . Enriched target, Ge (Li).     

Heterocyclic Spiro-naphthalenones. Part I: Synthesis and reactions of some spiro [(1 H-naphthalenone)-1,3′-piperidines]

The title compounds 14–16 were obtained via an intramolecular Mannich condensation by treating 11–13 with CH₂O at RT. The unsaturated ketones 14 and 15 were reduced to the allylic alcohols 18 and 19 respectively. Ring cleavage of compound 18 on treatment with 2N HCl gave the substituted aminopropanol 20 . The allylic alcohols 18 and 19 were hydrogenated to 22 and 23 respectively. With CH₂O, the amino-alcohol 23 gave the methano-naphthoxazocine 24 , whereas 22 and 23 , on heating in polyphosphoric acid (PPA), afforded the naphthazepines 25 and 26 respectively. With organolithium compounds, the unsaturated ketones 14 and 16 gave the teriary allylic alcohols 27–29 , which were hydrogenated and dehydrated to the olefins 36–40 ; these were cyclized via an intramolecular alkylation to the methanodibenzo-octahydrocyclooctapyridines 41–43 . On heating in PPA, the allylic alcohol 29 was converted into the naphthazepine 44 . With CH₂O, the naphthol 49 gave the naphthoxazocine 50 , in equilibrium with the spiro-naphthalene-pyrrolidinone 51 in solution. Finally, in the presence of CH₂O, the naphthazepine 57 afforded the methano-naphthazepinone 58 , which, by a 4-stage degradation, was transformed to the benzisoquinoline 62 .     

Total Synthesis of the Marine Sesquiterpene Quinones Hyatellaquinone and Spongiaquinone

The synthesis of the marine sesquiterpene quinone (+)‐hyatellaquinone ( 1 ) was achieved starting from the sesquiterpene aldehyde (+)‐albicanal ((+)‐ 3 ) (Schemes 3 and 4). Coupling of (+)‐albicanal with 2,3,5,6‐tetramethoxyphenyllithium led to the aryl‐sesquiterpene system, which was modified to the target molecule. Furthermore, the first total synthesis of the marine compound spongiaquinone ( 2 ) was carried out starting from ((?)‐albicanal (?)‐ 3 ) in a reaction sequence encompassing a stereoselective C?C bond hydrogenation and a one‐pot AcOH elimination/demethylation reaction (Schemes 7 and 10). The occurrence of 1,2‐ and 1,4‐benzoquinone forms of 1 and 2 depends on the pH of the solvent system.     

Sampling and Reconstruction in Distinct Subspaces Using Oblique Projections

Journal of Fourier Analysis and Applications - We study reconstruction operators on a Hilbert space that are exact on a given reconstruction subspace. Among those the reconstruction operator...     

Error estimates for the finite element solution of quasilinear obstacle problems *

This paper focusses on quasilinear second order differential operators. Concerning their strong monotonicity and Lipschitz continuity sufficient conditions are stated which are both explicit and easy to show. Applying these functional analytic properties to nonlinear obstacle problems we prove error estimates in energy norm for the finite element method with

linear trial functions.     

Molecular structures and spectroscopic characterization of cobalt(III) and nickel(II) complexes of <Emphasis Type="Italic">N</Emphasis>-(2-hydroxyethyl)-2-(thiophene-2-ylmethylene)-hydrazinecarbothioamide

Two complexes of a thiosemicarbazone ligand, namely N-(2-hydroxyethyl)-2-(thiophene-2-ylmethylene)-hydrazinecarbothioamide (HL), have been synthesized. The complexes have been characterized by physico-chemical and spectroscopic methods. The crystal and molecular structures of [CoL₃]·2MeOH (1) and [NiL₂] (2) have been determined by X-ray diffraction studies. For both complexes, the metal is coordinated through the sulfur and azomethine nitrogen atoms of the thiosemicarbazone. The ligand exists in its thiolate tautomeric form, and the central Co(III) and Ni(II) atoms have distorted octahedral and square planar geometries, respectively, with five-membered chelate rings formed by the ligand. The lattice of 1 shows infinite oxygen donor/acceptor hydrogen bonds in the ab plane and weak interactions between rings along the c axis, respectively, giving a supramolecular network. The molecular units in 2 are linked together by hydrogen bonds between the hydroxyl oxygen and hydrazone N proton, giving rise to an infinite ribbon extended along the c-axis. These chains are connected by N3–H3···O1 interactions that form a sheet within the ac plane.