Chemically resolved solid state NMR images of polymers

Polymers are generally spatially heterogeneous, either in terms of morphology or as blends of various components. Solid state NMR imaging provides a means of characterizing both the chemical/morphological composition and its spatial variation. Here we discuss multiple-pulse line-narrowing approaches to acquiring high resolution NMR images and how these sequences can be modified so as to be sensitive to the chemical composition of a sample.     

Exploring the activation of olefin polymerisation catalysts with density functional theory

Density Functional Theory has been used to study the activation of different olefin polymerisation catalysts by different activators. The results show that biscyclopentadienyl catalyst systems would act as the best catalysts and the activators of the type [CPh₃⁺][A⁻] would be the best at activating such systems. The competition between different species present in solution for the vacant active site in the catalyst was studied for the [(1,2Me₂Cp)₂ZrMe⁺][B(C₆F₅)₃CH₃⁻] system and the pre‐catalyst and AlMe₃ were found to be the compounds most likely to form dormant products in solution.     

An ab initio investigation of lithium ion hydration. II. Tetra‐ versus hexacoordination and halide complexes

The geometries and vibrational frequencies of Li(H₂O), n=4, 5, 6, 8, 18, and LiX(H₂O)_n, X=F, Cl, Br, I; n=3, 6 are calculated at various levels up to MP2/6‐31+G*. The solution structure and vibrational spectra with noncoordinating counterions are most consistent with our tetracoordinate lithium species. The solution spectra of lithium chloride and bromide solutions are consistent with our predicted spectra of ion pairs. It is shown that, to model the Li X vibrational mode correctly, both the lithium and halogen must be solvated with a sufficient number of waters. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 62–76, 2000     

Cross‐Coupling Reactions between Stable Carbenes

By utilizing stable carbenes with low‐lying LUMOs, coupling with the stable nucleophilic diaminocyclopropenylidene was achieved. This reaction resulted in the formation of two new and rare examples of a bent allene as well as the isolation of the first carbene–carbene heterodimer.     

Scaling laws in NMR scattering via dipolar fields

Breaking translational symmetry in magnetostatics imparts a scale dependence that is commonly investigated in physics (W. Warren et al., 1993, Science 262, 2005-2008). An interesting and important example arises in nuclear magnetic resonance studies involving the dipolar mean field of adjacent nuclear spins where the scattering (transfer of spatial spin gratings) via intermolecular macroscopic fields carries a signature of the local spatial distribution of the spin density. For arbitrary geometry, the inverse problem of extracting this spin distribution from experiments is intractable. Here we point out a simple, universal crossover in the scaling behavior at the sample's characteristic length scale, xi, of the species fluctuations in the sample along the measurement direction. This behavior is observed experimentally in an oil-water emulsion, an important representation of complex, heterogeneous, soft matter.