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The slow magic angle spinning 2D exchange NMR experiment applied to semicrystalline polyoxymethylene shows the existence of ultraslow molecular rotations in crystalline regions of the material. By simulating the two-dimensional spinning sideband spectra, which are characteristic for the molecular motion involved, it is found that a rotation of the polyoxymethylene helical chains over 200° is responsible for the observed spectra. The activation energy is 20 kcal/mol in good agreement with values obtained for the α relaxation in dynamic mechanical and dielectric studies.

Potentiometric titrations of solutions of various aromatic hydrocarbons in 1,2-dimethoxyethane and tetrahydrofuran with a solution of biphenylsodium have shown chemical reduction to proceed in two stages:R + e + R and R + e = R ' The reduction potentials of the aromatic hydrocarbons, calculated from the potentiometric curve, are in good agreement with the half-wave potentials The electrochemical series of aromatic hydrocarbons including a rough estimate of the standard potential of sodium in 1,Zdimethoxyethane and the mechanism of chemical reduction in inert and proton-active solvents are discussed.Introduction, Investigations on the polarographic reduction of conjugated hydrocarbons 1) have shown the reduction to be governed by the following primary reactions:

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In this paper we present an investigation of the remote nitrogen of imidazole in copper-doped I-histidine hydrochloride monohydrate, which is a model system for a wide range of biologically important copper-imidazole complexes. Since these systems are mostly not available in a crystalline form it is interesting to investigate to what extent information that can be obtained from these disordered systems using ESEEM techniques is reliable. From single crystal ESEEM and HYSCORE experiments we have determined the hyperfine and quadrupole coupling tensors of the remote nitrogen in this model system. Additionally, we determined information on these tensors from powdered material, independent of the single crystal results, using orientation selective multifrequency and two-dimensional experiments. The availability of the coupling tensors from the single crystal investigation allowed an assessment of the applicability of the employed powder techniques to this important class of systems. The two-dimensional stimulated echo experiment was found to be a very useful spectroscopic tool for the study of these systems when combined with simulations.