The synthesis and stereochemistry of some pyrido[3,4-d]carbazole derivatives

Pyrido[3,4-d]carbazole derivatives have been synthesised from N-acetyl-5-oxodecahydro-isoquinoline by the Fischer indole synthesis, and their stereochemistry established by ¹H-NMR spectroscopy. In contrast to experience with simpler systems, cyclisation in acetic acid gave only the alternative pyrido[3,4-a]-carbazole, and the desired pyrido[3,4-d]carbazole formation occurred only in the presence of sodium acetate.     

The crystal and molecular structures of π-arene complexes of the enneacarbonyltetracobalt cluster with ortho- and meta-xylene (a mixed crystal) and with benzene

Crystal structures of two π-areneenneacarbonyltetracobalt compounds are described. In the first the arene is a disordered 1/1 mixture of ortho and meta xylenes. The unit cell data are: space group P2₁/c (No. 14), Z = 4, a = 10.03(1), b = 9.86(1), c = 20.24(2) Å, β 96.40(5)°, V = 1991(1) ų. The final unweighted R value is 5.6% after anisotropic full-matrix refinement for 1883 independent reflections collected on a diffractometer using the θ – 2θ scanning technique. The second compound, benzeneenneacarbonyltetracobalt has unit cell data: space group R$\text{3}$ (No. 148), Z = 2, a = 9.79(3) Å, α 82.95(1)°, V = 920.8 ų. Full-matrix anisotropic refinement using 491 reflections yielded a final R of 3.3%. Both structures consist of a tetrahedral cobalt cluster, one cobalt atom is π bonded to the arene moiety, while the other three are each bonded to two terminal and two bridging carbonyl groups. Base to apex cobalt—cobalt distances average 2.481(2) Å while basal cobalt-cobalt distances average 2.455(2) Å. The distance from the apical cobalt to the arene centroid averages 1.62 A. The aromatic rings show no very significant distortion from local six-fold symmetry.     

Fluorinated phosphorus compounds: Part 9. The reactions of bis(fluoroalkyl) phosphorochloridates with oxygen nucleophiles

Twenty nine bis(fluoroalkyl) phosphates (R_FO)₂P(O)OR were prepared in 18-75% yield by treating phosphorochloridates (R_FO)₂P(O)Cl, where R_F was HCF₂CH₂, HCF₂CF₂CH₂, H(CF₂)₄CH₂, C₂F₅CH₂, C₃F₇CH₂, (CF₃)₂CH, (FCH₂)₂CH and (CH₃)₂CF₃C with methanol, ethanol, propanol and isopropanol in diethyl ether in the presence of triethylamine. The bulky chloridate [(CH₃)₂CF₃CO]₂P(O)Cl reacted with methanol, ethanol and propanol, but not with isopropanol - even on heating in the presence of the catalyst 4-dimethylaminopyridine - due to steric hindrance at phosphorus. The relative reactivities of three of the chloridates decreased in the order [(CF₃)₂CHO]₂P(O)Cl > [(FCH₂)₂CHO]₂P(O)Cl > [(CH₃)₂CF₃CO]₂P(O)Cl. Also described is the synthesis of phosphates (CF₃CH₂O)₂P(O)OCH₂R, where R = CH₂Br, CH₂Cl, CH₂F and CHF₂, and diphosphates [H(CF₂)_nCH₂O]₂P(O)OCH₂(CF₂)₂CH₂OP(O)[OCH₂(CF₂)_nH]₂, where n = 1, 2 and 4.     

Automated analysis of 13C/12C ratios in CO2 and dissolved inorganic carbon for ecological and environmental applications

Stable carbon isotope ratios (13C/12C) are a valuable tool for studying a wide range of environmental processes, including carbon cycling and subsurface microbial activity. Recent advances in automated analysis provide the opportunity to increase greatly the ease and consistency of isotopic analysis. This study evaluated an automated headspace sampler linked to a commercially available CO2 preconcentration system and continuous flow isotope ratio mass spectrometer. Field sampling and analysis methods are illustrated for delta13C of soil respired CO2, from both tracer and natural abundance experiments, and dissolved inorganic carbon from contaminated groundwater. The automated system demonstrated accuracy, precision, and linearity, with standard errors below 0.1 per thousand for replicate gas standards run at concentrations varying five-fold. It measured 40 samples per 10-hour run, with concentrations ranging from ppb to percentage levels. In the field, gas samples were injected into nitrogen-filled autosampler vials, thereby allowing use of small sample volumes, control of analyte concentration, and direct analysis by the automated system with no further preparation. A significant linear relationship between standard concentrations and peak area allows for accurate estimates of sample CO2 concentration from the mass spectrometric data. The ability to analyze multiple small-volume samples with minimal off-line preparation should enhance the application of isotopes to well-replicated field experiments for process-level studies and spatial and temporal scaling.