Polymers for catalytic cation radical chemistry

Cation radical polymers which have cation radical functions at up to 5% of the poly(styrene) monomer sites have been prepared, and their effectiveness in catalyzing the cation radical Diels-Alder reaction is demonstrated.     

Sequential versus direct multiphoton absorption

We present results of exact calculations on a three-level Morse oscillator modeling HF which suggest that multiphoton absorption proceeds by sequential single-level transitions, transitions arising from coupling between non-adjacent states being dynamically negligible. The time-dependent Schrödinger equation is integrated in the Floquet formalism.     

Uniform thin films of poly-3,4-ethylenedioxythiophene (PEDOT) prepared by in-situ deposition

In-situ deposited thin films of the conducting polymer poly-3,4-ethylenedioxythiophene (PEDOT) have been prepared on hydrophilic and hydrophobic substrates and characterized by UV-Vis spectroscopy, atomic force microscopy and resistivity measurements.     

The thermodynamics of dilution ofn-dodecyltrimethylammonium bromide micelles in aqueous solutions

Summary The relative partial molal thermodynamic functions ₁ and have been derived from reported experimental light scattering and calorimetric measurements on micellar solutions ofn-dodecyltrimethylammonium bromide. It is shown that the magnitudes of the thermodynamic functions are considerably larger than can be accounted for by the interaction of the electrical double layers surrounding the micelles. Possible enthalpy changes arising from a change in micelle shape, size and degree of dissociation on dilution are discussed.

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Zusammenfassung Die relativen molaren thermodynamischen Partialfunktionen , andS ₁wurden abgeleitet aus Literaturwerten von Lichtstreuungsmessungen und kalorimetrischen Untersuchungen an mizellaren Lösungen vonn-Dodecyltrimethylammoniumbromid. Es wird gezeigt, daß die Zahlenwerte der thermodynamischen Funktionen erheblich größer sind als von der Wechselwirkung der elektrischen Doppelschichten zu erwarten ist, die die Mizellen umgeben. Mögliche Enthalpieänderungen, die sich aus Änderungen von Größe, Gestalt und Dissoziationsgrad bei Verdünnung herleiten, werden diskutiert.

     

Second-order nonlinear optical properties of the Ag(111)/electrolyte interface in the presence of self-assembled monolayers containing conjugated pi systems. I. Alpha-functionalized terthiophene films on Ag(111)

The nonlinear optical properties of self-assembled monolayers obtained from bonding two different alpha-functionalized terthiophenes (alpha-T3) to (111) silver electrode surfaces have been investigated using second harmonic generation (SHG). The two (alpha-T3) compounds used were functionalized with alkane chains of different lengths (C8 and C4), and each was terminated with a thiol anchoring group. A nitrile group was attached to the terminal thiophene ring of the (alpha-T3) compound with the C4 chain. The orientation of the polarization of the incident beam was changed systematically and gradually between "p" and "s" orientation and the SH signal (isotropic and anisotropic contributions) analyzed in both directions ("P" and "S"). The symmetry of the system was reduced by the presence of the adlayers from C3v to C3. The dependence on the applied potential and the incident wavelength has also been studied. The relative magnitudes and phases of the various second-order tensor elements have been estimated and compared with the values for a bare surface. A resonance process in the (alpha-T3) pi moiety has been investigated, and from this, the effective "band-gap" energies of the organic semiconductor SAMs (i.e., the energy difference between the pi-pi bands) have been estimated.     

A reoptimization of the five-site water potential (TIP5P) for use with Ewald sums

The five-site transferable interaction potential (TIP5P) for water is most accurate at reproducing experimental data when used with a simple spherical cutoff for the long-ranged electrostatic interactions. When used with other methods for treating long-ranged interactions, the model is considerably less accurate. With small modifications, a new TIP5P-like potential can be made which is very accurate for liquid water when used with Ewald sums, a more physical and increasingly more commonly used method for treating long-ranged electrostatic interactions. The new model demonstrates a density maximum near 4 degrees C, like the TIP5P model, and otherwise is similar to the TIP5P model for thermodynamic, dielectric, and dynamical properties of liquid water over a range of temperatures and densities. An analysis of this and other commonly used water models reveals how the quadrupole moment of a model can influence the dielectric response of liquid water.     

Highly substituted pyridines via tethered imine-enamine (TIE) methodology

A tethered imine-enamine methodology has been developed for the direct conversion of 1,2,4-triazines into highly substituted pyridines via the inverse electron demand Diels-Alder reaction which avoids the need for a discrete aromatisation step. This TIE methodology has also been applied in one pot reaction cascades involving 1,2,4-triazines and utilising MnO(2)-mediated tandem oxidation processes (TOPs).     

Applying the phenol red colorimetric method for bromide analysis to reducing waters

Chemical species present in reducing waters have the potential to produce severe negative interferences by consuming the chloramine T (CT) which is used as the oxidising agent in the phenol red-based calorimetric method for trace bromide analysis. Mn(2+) and Fe(2+) were found not to interfere at concentrations up to 200muM. However, hydroxylamine (NH(2)OH), which can be present in both ground-and surface-waters, exerts a strong negative interference. A method involving pre-treatment with permanganate and hydrogen peroxide has been developed for the destruction of NH(2)OH prior to adding the colour reagents. The procedure is not only compatible with the chemistry of the calorimetric method, but is also robust and technically easy to implement.     

Effect of ether versus ester tethering on Heck cyclizations

Ether tethers allow Heck cyclizations to proceed in high yields. Ester tethers lead to low yields. Styrene trapping experiments indicate that ester reactions form viable organopalladium intermediates that cannot cyclize efficiently.     

Boron-containing nucleosides. 1. Synthesis of the novel heterocycle 2-benzyl-1,4-dihydro-1-hydroxythieno[3,2-c][1,5,2]diazaborin-3(2H)-one: A thieno-fused 4-borauracil

The synthesis of the novel boron-containing nucleobase 2-benzyl-1,4-dihydro-1-hydroxythieno[3,2-c]-[1,5,2]diazaborin-3(2H)-one ( 8 ), a thieno-fused 4-borauracil, is described. Compound 8 was prepared in three steps starting from 2-thiophenecarbonyl chloride ( 4 ). A multinuclear and multisolvent nmr study of 8 indicates that the boron atom maintains a trigonal geometry in the solvents used.