Improved Preparation of 1,3-Bis(2,6-di-iso-propylphenyl)imidazolium Tetrafluoroborate

A convenient, high-yielding, multi-hundred-gram preparation of 1,3-bis(2,6-di-iso-propylphenyl)imidazolium tetrafluoroborate is described. The preparation of this salt has significant advantages over the chloride as it eliminates potential bis(chloromethyl) ether formation. The improved conditions provided the tetrafluoroborate salt in 61% overall yield in two steps from 2,6-di-iso-propylaniline.     

Dibenzyl Structuresin a Macromolecular Chain. III. Dibenzyldiisocyanates Reactivity

The reactivity of the 2,2′-, 2,4′-, 4,4′-dibenzyldiisocyanate (2,2′-, 2,4′-, 4,4′-DBDI) with n-butanol in benzene has been studied. The concentrations of all species were monitored by using high performance liquid chromatography (HPLC). The reactivity of 4,4′-DBDI is similar to that of 4,4′-diphenylmethanediisocyanate (4,4′-MDI). Very strong intramolecular catalytic effects were noticed in the case of 2,2′-DBDI, probably due to the variable molecular geometry. These effects are responsible for the whole reaction pattern. The 2,4′-DBDI NCO ortho and para groups reactivities are different and comparable to that of 2,4-toluylenediisocyanate (2,4-TDI).     

Detection of explosive-related compounds by laser photoionization time-of-flight mass spectrometry

We report studies using laser photoionization and time-of-flight mass spectrometry to detect several explosive-related compounds (ERCs). The ultimate goal of this work is the detection of buried land mines through their chemical signatures. Resonantly enhanced multiphoton ionization using jet expansion cooling, with a nanosecond pulse laser, results in complete photofragmentation of the parent ERC and appearance only of the NO⁺ ion, which forms all of the detected signal. This will also occur for compounds naturally occurring in the environment, such as NO₂ or peroxyacetylnitrate, rendering too many false alarms for this approach to be viable. Therefore, two other techniques were evaluated. Single-photon ionization with nanosecond pulses in the vacuum ultraviolet is shown to produce only the parent ion, and is probably the most suitable choice. For 2,4-dinitrobenzene we find a limit of detection of about 40 ppb, for a signal to noise ratio of 3. This may be sufficient for land-mine detection, but improvement is likely with future work. Nonresonant multiphoton ionization in the ultraviolet with a femtosecond laser produces fragmentation but retains some parent ERC ion signal. The limit of detection is similar to that of single-photon ionization but it is harder to implement with lasers now commercially available. Future directions are outlined. PACS 07.07.Df; 33.80.Rv; 82.80.Ms; 82.80.Rt     

A new approach to the synthesis of polycyclic structures

A general, convergent approach to the synthesis of polycyclic structures has been developed, based on the tandem radical addition/cyclisation of xanthates to dienones followed by an ionic ring closure to give, finally, a number of variously substituted tricyclic compounds.     

Palladium-catalyzed 1,3-butadiene telomerization with methanol. Improved catalyst performance using bis-o-methoxy substituted triarylphosphines

New, improved phosphine ligands for palladium-catalyzed butadiene telomerization with methanol have been discovered. Using high throughput experimentation and an Electrospray Ionization-Mass Spectrometry (ESI-MS) investigation of telomerization catalysts solutions, we have identified phosphines of the type P(C₆H₄-2-OMe)₂(C₆H_5−n(X)_n), where X is an electron-withdrawing group, as high selectivity, high activity phosphine ligands for butadiene telomerization with methanol to 1-methoxy-2,7-octadiene (MOD-1). These ligands were designed to mitigate anaerobic oxidation of phosphines by alkylation which was shown by Electrospray Ionization-Mass Spectrometry (ESI-MS) studies to correlate with catalyst death and palladium precipitation in working telomerization catalyst solutions. The best phosphine-promoted catalysts achieve selectivities to desired 1-methoxy-2,7-octadiene of 94% at high butadiene conversion, significantly improved over those achieved commercially by triphenylphosphine.     

Coherent state transfer between an electron and nuclear spin in (15)N@C(60)

Electron spin qubits in molecular systems offer high reproducibility and the ability to self-assemble into larger architectures. However, interactions between neighboring qubits are "always on," and although the electron spin coherence times can be several hundred microseconds, these are still much shorter than typical times for nuclear spins. Here we implement an electron-nuclear hybrid scheme which uses coherent transfer between electron and nuclear spin degrees of freedom in order to both effectively turn on or off interqubit coupling mediated by dipolar interactions and benefit from the long nuclear spin decoherence times (T(2n)). We transfer qubit states between the electron and (15)N nuclear spin in (15)N@C(60) with a two-way process fidelity of 88%, using a series of tuned microwave and radio frequency pulses and measure a nuclear spin coherence lifetime of over 100 ms.     

Book Received

Superionic conductors have high ionic conductivity because of extensive disorder in a component sublattice of the solid. Knowledge of the nature and extent of the disorder and its dynamics is essential for detailed understanding of superionic behaviour. The present article contains an outline of experimental techniques used to obtain this knowledge and describes results of their application to a variety of superionic materials.     

Variational calculations of the static polarizability of H2 and of the dipole-dipole contribution to the dispersion energy between two hydrogen molecules

The convergence of variation-perturbation calculations using non-linear variation parameters has been examined for the static polarizability of H₂ and for the coefficient (C₆) of the R ^-6 term in the multipole expansion of the H₂-H₂ dispersion energy. Using a correlated ground state wavefunction, and one excited state for each of the parallel and perpendicular components of the polarizability, a single variational parameter for each state gave 96 per cent of the exact value of α_⊥ and 91 per cent of the exact value of α_‖. A second variational parameter for the parallel component gave 94 per cent of α_‖. The same procedure gave the spherical average and anisotropy of C₆ to an accuracy of about 90 per cent. By extending the calculations into the region where overlap of the orbitals of the two molecules becomes significant, it is shown for the end-on configuration that the C₆ R ^-6 term underestimates the dispersion energy near the van der Waals' minimum by roughly 10 per cent.     

Static secondary ion mass spectrometry of organic plasma-deposited films created from stable isotope-labeled precursors. II. Mixtures of acetone and oxygen

A series of plasma-deposited films (PDFs), created by blending controlled ratios of acetone vapor and oxygen in the feed to the plasma reactor, were analyzed by static secondary ion mass spectrometry (SIMS). Examination of the quadrupole-based static SIMS fragmentation patterns of acetone–O₂ PDFs created from ¹³C-labeled acetone generally allowed the hydrocarbon secondary ions to be distinguished from oxygen-containing secondary ions. These results were compared with those obtained via high-mass resolution time-of-flight (TOF)-SIMS. The identified secondary ions were then assigned structural attributes, based on comparison of the static SIMS spectra of the acetone–O₂ PDFs with those of conventional hydrocarbon and oxygen-containing polymers. A preliminary investigation to unravel the mechanism of oxygen incorporation in the acetone–O₂ PDFs from the two plasma feed components was undertaken through the analysis of PDFs created from 1,2,3¹³C₃-acetone(¹⁶O) vapor and ¹⁸O₂ gas.