Unexpected Z/E isomerism of N-methyl-O-phosphothioyl benzohydroxamic acids,their oxyphilic reactivity and inertness to amines

Structural Chemistry - Thiophosphinoylation of N-methyl p-substituted benzohydroxamic acids using disulfanes (method A) or diphenylphosphinothioyl chloride (method B) provides only one conformer of...     

Proton dynamics in the strong chelate hydrogen bond of crystalline picolinic acid N-oxide. A new computational approach and infrared, raman and INS study

Infrared, Raman and INS spectra of picolinic acid N-oxide (PANO) were recorded and examined for the location of the hydronic modes, particularly O-H stretching and COH bending. PANO is representative of strong chelate hydrogen bonds (H-bonds) with its short O...O distance (2.425 A). H-bonding is possibly well-characterized by diffraction, NMR and NQR data and calculated potential energy functions. The analysis of the spectra is assisted by DFT frequency calculations both in the gas phase and in the solid state. The Car-Parrinello quantum mechanical solid-state method is also used for the proton dynamics simulation; it shows the hydron to be located about 99% of time in the energy minimum near the carboxylic oxygen; jumps to the N-O acceptor are rare. The infrared spectrum excels by an extended absorption (Zundel's continuum) interrupted by numerous Evans transmissions. The model proton potential functions on which the theories of continuum formation are based do not correspond to the experimental and computed characteristics of the hydrogen bond in PANO, therefore a novel approach has been developed; it is based on crystal dynamics driven hydronium potential fluctuation. The envelope of one hundred 0 --> 1 OH stretching transitions generated by molecular dynamics simulation exhibits a maximum at 1400 cm-1 and a minor hump at approximately 1600 cm-1. These positions square well with ones predicted for the COH bending and OH stretching frequencies derived from various one- and two-dimensional model potentials. The coincidences with experimental features have to be considered with caution because the CPMD transition envelope is based solely on the OH stretching coordinate while the observed infrared bands correspond to heavily mixed modes as was previously shown by the normal coordinate analysis of the IR spectrum of argon matrix isolated PANO, the present CPMD frequency calculation and the empirical analysis of spectra. The experimental infrared spectra show some unusual characteristics such as large temperature effects on the intensity of some bands, thus presenting a challenge for theoretical band shape treatments. Our calculations clearly show that the present system is characterized by an asymmetric single well potential with no large amplitudes in the hydronium motion, which extends the existence of Zundel-type spectra beyond the established set of hydrogen bonds with large hydronic vibrational amplitudes.     

Conformational analysis of N-isopropylbenzohydroxamic acids: crystal structure, DFT, and NMR studies

X-ray crystal structure determinations together with density functional theory (DFT) calculations in vacuo and NMR studies in solution have been carried out for 4-MeOC₆H₄CONPrⁱOH 2a and 3,5-(NO₂)₂C₆H₃CONPrⁱOH 2b. The results were compared with that for the respective N-methyl benzohydroxamic acids. For crystal structures as well as for DFT-optimized geometries of 2 (both isomers) in vacuo, the effect of substituents in aromatic ring manifested by changing of charges is inconspicuous. Studies of potential energy surfaces showed that libration barrier around ω ₁ = 0° is low enough to make electron conjugation feasible, and that for 2b rotation barrier around C(O)N bond is higher by 6 kcal/mol and additionally, that rotation around N–C bond is hindered. A careful analysis of low-temperature ¹H NMR spectra confirmed the greater stability of Z-2a, the greater rigidity of E-2b and the influence of solvent on both isomers population. Despite solvent-dependent conformational alteration, both 2a and 2b crystallize exclusively as E isomers from ethyl acetate solution. Correlations of absolute ¹H, ¹³C, and ¹⁵N shielding calculations with experimental data were also analyzed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Simulation and optimization of 2.6–2.8 μm GaSb-based VCSELs

We present the simulation results of threshold operation of mid-infrared GaSb-based vertical-cavity surface-emitting lasers (VCSELs) obtained with the use of comprehensive fully self-consistent optical-electrical-thermal-recombination numerical model. The results show that by a proper design of VCSEL structure and composition of the active region it is theoretically possible to achieve room-temperature (RT) threshold operation for wavelength of 2.8 μm which is about 0.2 μm longer than those reported so far in the literature for III-V VCSELs with type-I quantum wells. Calculated values of the RT threshold current were equal to 2.5 and 4.0 mA for tunnel-junction diameters of 2 and 4 μm, respectively.     

The effect of uncertain material properties on free vibrations of thin periodic plates

Thin periodic plates with uncertain properties in a periodicity cell are investigated. To describe dynamics of these plates the non-asymptotic tolerance modelling method, cf. Wo?niak and Wierzbicki (Averaging techniques in thermomechanics of composite solids. Wydawnictwo Politechniki Cz?stochowskiej, Cz?stochowa, 15), Wo?niak et al. (eds.) (Thermomechanics of microheterogeneous solids and structures. Tolerance averaging approach. Wydawnictwo Politechniki ?ódzkiej, ?ód?, 16), for those plates is applied. The governing equations of tolerance models based on this method take into account the effect of period lengths on the overall behaviour of the plate. Hence, the additional effects of the periodicity can be analysed, as higher order vibrations. Moreover, properties of the plate in the periodicity cell are determined uncertainly. To analyse an influence of random variables of the properties with a fixed probability distribution on vibrations of the plate the Monte Carlo analysis is applied.     

Physicochemical properties of Mn1.45Co1.45Cu0.1O4 spinel coating deposited on the Crofer 22 H ferritic steel and exposed to high-temperature oxidation under thermal cycling conditions

Journal of Thermal Analysis and Calorimetry - The Crofer 22 H ferritic steel substrate was coated with an Mn1.45Co1.45Cu0.1O4 spinel by means of electrophoresis. After high-temperature oxidation...     

Synthesis and reactions of the optically active selenols derived from monoterpenes

A convenient methodology for the synthesis of optically active selenols, derived from p-menthane, carane, and pinane, is described. The selenols were oxidized with air to give the optically active diselenides, and were also converted into the corresponding allylic selenides via reaction with Z- and E-cinnamyl, geranyl, and neryl chlorides. Oxidation of the allylic selenides with mCPBA gave the optically active alcohols via [2,3]-sigmatropic rearrangement of the in situ generated allylic selenoxides.     

Cadmium complex possessing simultaneously silanethiolato- and dithiocarbamato-ligands. A novel single-source precursor of cadmium sulfide

Thermal decomposition of suitable coordination compounds may be used as efficient route for fabrication of semiconducting layers. A new potential CdS precursor—a cadmium complex with all-sulfur Cd-coordination sphere [Cd{μ-SSi(OBu ^t )₃}(S₂CNC₄H₈)]₂ 1—has been prepared, and its properties are investigated. The complex was obtained in the reaction between dimeric bis(tri-tert-butoxysilanethiolato)cadmium(II) [Cd{SSi(OBu ^t )₃}₂]₂ and ammonium N,N-tetrametylene-dithiocarbamate and characterized by spectral methods (IR, UV–Vis, MS, and NMR). X-ray structure analysis revealed the complex as molecular and dimeric in solid state with each of chelating dithiocarbamate ligands bonded to one Cd center and sulfur atoms from two tri-tert-butoxysilanethiolato ligands bridging metallic centers and thus completing the CdS₄ coordination sphere. Thin film of the precursor prepared on SiO₂ substrates via spin-coating technique was analyzed by AFM. Its decomposition was studied by thermal analysis methods (TG, DSC, and TG-FTIR). After melting at 227 °C, [Cd{μ-SSi(OBu ^t )₃}(S₂CNC₄H₈)]₂ undergoes endothermic decomposition leading to CdS as the only solid product further identified by XRD, EDS, FIR as hexagonal CdS form. Its morphology is characteristic and may be described as “micro-noodles”.