Reactions of 1-alkyl-1,2-diphospholes with 1,3-dipoles: diphenyldiazomethane and nitrones

The reaction of 1-alkyl-1,2-diphosphacyclopenta-2,4-dienes (1-alkyl-1,2-diphospholes) (1) with diphenyldiazomethane proceeds at room temperature via unstable [3+2] cycloadducts to form bicyclic phosphiranes (2). However, 1-alkyl-1,2-diphospholes (1) react with N,alpha-diphenylnitrone or N-tert-butyl-alpha-phenylnitrone depending on the temperature to give either dimers of 1-alkyl-1-oxo-1,2-diphospholes (5) or 1-alkyl-1,7-dioxo-6-azo-1,7-diphospha-bicyclo[3.2.0]hept-2-enes (7) - phosphorus analogues of β-lactams.     

A comparative study of trace enrichment of chlorophenols in water by extraction with C6 and C8 alkanes and by C18 reversed-phase adsorption

The efficiency, reproducibility and sensitivity ofn-hexane and iso-octane extraction and of C₁₈ reversed-phase adsorption for accumulation of 4-chloro-, 2,4-dichloro-, 2,4,5- and 2,4,6-trichloro-, 2,3,4,6-tetrachloro- and pentachlorophenol from aqueous solutions were compared. In extraction procedures the acetyl and pentafluorobenzoyl derivatives of chlorophenols were extracted from water. In adsorption procedure chlorophenols adsorbed on a Sep-Pak C₁₈ cartridge were eluted with acetone and after that derivatized analogously.All three procedures were found to be applicable for an efficient trace enrichment of chlorophenols in water, the proper choice being dependent on the required sensitivity of the analysis. Lower detection limits of single compounds at 10 ng·1^–1 levels were achieved by adsorption procedure owing to the more uniform and for most chlorophenols higher adsorption than extraction recoveries as well as owing to the possibility of treating larger volumes of water samples. The extraction procedure could be successfully applied to the concentrations of chlorophenols in water 1g·1^–1.Owing to its higher efficiency and better sensitivity the C₁₈ reversed-phase adsorption procedure was chosen as the more suitable one for the determination of chlorophenol levels in surface, ground and drinking waters. The conversion of chlorophenols accumulated from a water sample parallel to both acetyl and pentafluorobenzoyl derivatives and the analysis of both types of derivatives on two basically different gas Chromatographic columns were recommended for a more reliable identification and quantitation of the compounds analyzed.     

CO2/CO2 isotopic ratio measurements with a continuous-wave quantum cascade laser in exhaled breath

A laser spectrometer based on a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser at ∼2308 cm⁻¹ has been evaluated for measurement of ¹³CO₂/¹²CO₂ isotopic ratio (δ¹³C) changes in exhaled breath samples and in CO₂ gas flows in the concentration range 1-5%. Mid-infrared CO₂ absorption spectra were measured in a 54.2-cm long optical cell using balanced detection whereby the beam passing through the cell was ratioed against a reference beam split-off from the main beam before the cell. Signal-to-noise ratios (SNR) were estimated for CO₂ concentration measurements determined from either absorption peak amplitude or absorption peak area. The highest SNR were achieved in the measurements based upon a fitted absorption peak area. Typical short-term δ¹³C precisions of 1.1⁰/₀₀ (1-s integration time) and 0.5⁰/₀₀ (8-12-s integration time) were estimated from the two-sample (Allan) variance plots of data recorded in the optical cell at a pressure of 20 Torr and with no active temperature stabilization of the cell and gas flow. The best precision of 0.12⁰/₀₀ was achieved for averaging 80 successive 1-s integration time measurements.     

Reactivity of Sodium Pentaphospholide Na[cyclo-P5] towards C≡E (E=C,N, P) Triple Bonds

A diglyme solution of Na[cyclo-P₅] ( 1 ) reacts with alkynes and isolobal nitriles and phosphaalkynes to afford the otherwise elusive (aza)phospholide anions 2 a – c , 4 a,b , and 6 . The reaction of Na[cyclo-P₅] with alkynes and nitriles was studied by means of DFT methods, which suggested a concerted mechanism for the formation of 2 a and 4 b . The anions 2 a – c , 4 a,b , and 6 coordinate in an η⁵-fashion towards Fe^II to give the sandwich (aza)phosphametallocenes 3 a – c , 5 a,b and 7 in moderate to good yields. The new compounds were characterized by means of multinuclear NMR spectroscopy, single-crystal X-ray diffraction and cyclic voltammetry.     

The atomistic origin of the inverse piezoelectric effect in α-quartz

Ab initio calculations have been carried out using the FP-APW+lo method in order to understand the atomic origin of the inverse piezoelectric effect in α-quartz. The external electric field was modelled by a saw-like potential V_ext in order to achieve translational symmetry within a supercell (SC) containing 72 atoms. The original trigonal quartz structure was repeated along the [110] direction, which corresponds to the direction of the external field. An electric field with 550 kV/mm was applied and the atomic positions of the SC were relaxed until the forces acting on the atoms vanished. In parts of the SC, V_ext changes almost linearly and thus the relaxed atomic positions can be used to determine the structural response due to the external electric field. The calculations provide the piezoelectric modulus of the correct order of magnitude. In contrast to previous models and in agreement with recent experimental results, the atomic origin of the piezoelectric effect can be described by a rotation of slightly deformed SiO₄ tetrahedra against each other. The change of the Si-O bond lengths and the tetrahedral O-Si-O angles is one order of magnitude smaller than that of the Si-O-Si angles between neighbouring tetrahedra. The calculated changes of X-ray structure factors are in agreement with experiment when the theoretical data are extrapolated down to the much smaller field strength that is applied in the experiment (E<10 kV/mm).     

Pressure broadening parameters of the hydroxyl radical A 2 Σ+ (υ’=0) ← X 2 Π3/2 (υ=0) transitions at ca. 308 nm

Pressure broadening widths and pressure-induced frequency shifts for the hydroxyl radical Q11([see full textsee full text]), Q21([see full textsee full text]), Q11(2), Q21(2) absorption lines in the A band at ca. 308 nm have been determined in the presence of a variety of gases (N2, Ar, Ne and He). Hydroxyl radicals were formed using either a microwave discharge or a vacuum ultra-violet photolysis of water vapour and were detected using direct absorption spectroscopy with a bandwidth normalised noise equivalent absorption sensitivity of 5 ×10-5 Hz-1/2. A tunable external cavity diode laser at 835 nm and a single-frequency continuous-wave intracavity frequency-doubled diode laser at 488 nm were used to produce tunable continuous-wave light at 308 nm by sum-frequency generation in a -BaB2O4 crystal.     

Electron-phonon interaction and transport in semiconducting carbon nanotubes

We calculate the electron-phonon scattering and binding in semiconducting carbon nanotubes, within a tight-binding model. The mobility is derived using a multiband Boltzmann treatment. At high fields, the dominant scattering is interband scattering by LO phonons corresponding to the corners K of the graphene Brillouin zone. The drift velocity saturates at approximately half the graphene Fermi velocity. The calculated mobility as a function of temperature, electric field, and nanotube chirality are well reproduced by a simple interpolation formula. Polaronic binding give a band-gap renormalization of approximately 70 meV, an order of magnitude larger than expected. Coherence lengths can be quite long but are strongly energy dependent.     

Effect of exciton-phonon coupling in the calculated optical absorption of carbon nanotubes

We find that the optical properties of carbon nanotubes reflect remarkably strong effects of exciton-phonon coupling. Tight-binding calculations show that a significant fraction of the spectral weight of the absorption peak is transferred to a distinct exciton+phonon sideband, which is peaked at around 200 meV above the main absorption peak. This sideband provides a distinctive signature of the excitonic character of the optical transition. The exciton-phonon coupling is reflected in a dynamical structural distortion, which contributes a binding energy of up to 100 meV. The distortion is surprisingly long ranged, and is strongly dependent on chirality.