Semicarbazones and thiosemicarbazones,XIII: Study of the hydrolysis of coordinated thiosemicarbazones

Summary The hydrolysis of coordinated thiosemicarbazones was studied. It was found that the nickel(II) ion promotes the reaction. Steric and electronic influences were found. The hydrolysis ofATSC in the trigonal bipyramid compounds [M(ATSC)₂Cl]Cl [M=Fe(II), Co(II), Ni(II)], is higher with the Ni(II) complex, the compound with the shorterM-N distance.

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Semicarbazone und Thiosemicarbazone, 13. Mitt.: Untersuchungen zur Hydrolyse koordinierter Thiosemicarbazone

Zusammenfassung Bei der Hydrolyse von koordinierten Thiosemicarbazonen wurde festgestellet, daß das Nickel(II)-Ion die Reaktion begünstigt. Es wurden sterische und elektronische Einflüsse gefunden. Die Hydrolysengeschwindigkeit desATSC im trigonal bipyramidalen Komplex [M(ATSC)₂Cl]Cl [M=Fe(II), Co(II), Ni(II)] ist höher mit dem Ni(II)-Komplex, der Verbindung mit der kürzerenM-N-Distanz.

     

Is 2-cyclopropylpropene really gauche?

Infrared spectra of gaseous and solid 2-cyclopropylpropene (2-CPP, c-C3H5C (CH3)CH2) have been recorded from 3500 to 40 cm-1, and Raman spectra (3200-150 cm-1) of the liquid as well as mid-infrared spectra of 2-CPP in liquid krypton solution (from -105 to -150 degrees C) were also obtained. Ab initio calculations, with basis sets up to 6-311+G(2df, 2pd), were carried out for this molecule, using the restricted Hartree-Fock (RHF) approach, with full electron correlation by the perturbation method to second order (MP2(full)) and density functional theory (DFT) by the B3LYP method. The combination of the experimental and computational results (particularly with the higher basis sets) unequivocally identifies the more stable conformer of 2-CPP as the trans form, with the gauche rotamer higher in energy, but also stable. The cis structure of this compound is not observed experimentally, and is predicted by the computational approaches to be a transition state. By studying the temperature variation of two well-resolved sets of conformational doublets of 2-CPP dissolved in liquid krypton, an average enthalpy difference between conformers of 182+/-18 cm-1 (2.18+/-0.22 kJ mol-1) has been determined, with the trans conformation lower in energy in the fluid states, and the sole conformer present in the polycrystalline solid phase. This enthalpy difference corresponds to an ambient temperature conformational equilibrium in the fluid phases of 2-cyclopropylpropene containing approximately 55+/-2% of the more stable trans rotameric form. A complete vibrational assignment for the trans conformer of 2-CPP is given, and many of the bands of the gauche rotamer have also been assigned. Structural parameters, dipole moments, and rotational constants for this molecule have been calculated at the MP2(full)/6-311+G(d,p) level, and these results--as well as the results from the experimental studies--are compared to similar quantities in related compounds.     

Photochemical synthesis of benz[h]isoquinolines

The synthesis of benz[h]isoquinolines has been achieved using a highly convergent photochemical method. The approach presented provides ready access to biologically active compounds and building blocks not readily available through other methods.     

Temperature-insensitive strain measurement using differential double Bragg grating technique

A novel differential double Bragg grating sensor for temperature-insensitive strain measurement is presented. The sensor consists of two identical weak measuring and reference gratings separated by some distance. The reference grating is placed inside the silica capillary that made it almost strain insensitive. The basic idea in differential double Bragg grating sensor is to measure the energy of the oscillating term in the reflection spectrum of double Bragg grating structure. The normalized energy of the interference term depends on the pitch difference of the two gratings and does not change when pitch variations of both gratings are equal with temperature variation. Therefore, the normalized energy of the interference term can be used for the temperature-insensitive strain measurement.     

Formation of sub-micron size carbon structures by plasma jets emitted from a pulsed capillary discharge

We have performed an experimental investigation of the potential use of intense plasma jets produced in a repetitive pulsed capillary discharge (PCD) operating in methane gas, to irradiate Si (1 0 0) substrates. The surface modifications induced by the plasma jet using two different material inserts at the capillary end, graphite and titanium, are characterized using standard surface science diagnostic tools, such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and Raman spectroscopy (RS). It has been found that the application of methane plasma jet results in the formation of sub-micron size carbon structures. It is observed that the resulting plasma irradiated surface morphologies are different, depending on the different material inserts used at the capillary end, at otherwise identical operational conditions. To investigate the species responsible for the observed surface changes in different material inserts to the capillary, optical-emission spectroscopy (OES) was recorded using a 300-1000 nm spectrometer. The OES results show the presence of H, CH and C₂ Swan band in the discharge plasma, which play a significant role in the formation of the carbon structures.     

Calix[4]bipyrrole--a big, flexible, yet effective chloride-selective anion receptor

Anion binding studies reveal that, in spite of its big size and flexible structure, calix[4]bipyrrole shows strong anion binding in general and good selectivity towards chloride anion in acetonitrile.     

Diffusion coefficients in swelling polypyrrole: ESCR and Cottrell models

Reliable diffusion coefficients, D, for the diffusion of perchlorate anions into polypyrrole films during polymeric oxidation were obtained from chronoamperometric results. Two different models were used to calculate D: the Cottrell equation and the electrochemically stimulated conformational relaxation (ESCR) model. As expected, the initial Cottrell hypothesis was far from swelling/shrinking polymeric electrodes and the obtained D range was from 10(-10) to 10(-6) cm(2) s(-1). The ESCR model, based on the internal diffusion that takes place from regions where the steady state of oxidation has already been reached to regions where the oxidation is only just beginning, provided values of D ranging from 0.4 x 10(-9) to 2.2 x 10(-9) cm(2) s(-1), which is close to the values expected for a gel. When a constant amplitude is kept for the potential step, D increases with increasing initial anodic potentials, i.e., from increasingly swollen films. When it is stepped to the same oxidation potential, D decreases when starting from more cathodic potentials, i.e., from a more compact structure. These changes in D can be attributed to (i) swelling processes during oxidation, giving a gel-like structure; (ii) compacting processes at increasing cathodic potentials; (iii) the increasing thickness of the film during oxidation; and (iv) a decrease in film viscosity during the swelling process.     

Materials chemistry approach to anion-sensor design

A new approach to sensing of aqueous phosphate-related anions based on chromogenic conductive polymers is demonstrated. The anion-sensor affinity can be adjusted by externally applied voltage. Introduction of p-doping to the polymers results in augmented anion sensitivity, which is ascribed to the effect of synergy between low-level p-doping in a polythiophene polymer and hydrogen bonding. The chromogenic conductive polymer films display anion-specific changes in color, conductivity, and mass upon increasing concentration of anions.     

Thermally induced cascade pericyclic reaction pathways from tetraene esters

A novel thermally induced cascade pericyclic transformation of a tetraene ester into a complex tricyclic core is reported. This transformation is high yielding and highly selective.