Ternary and quaternary layered nitride halides, Ca2N(X,X′) (X,X′=Cl, Br, I): Evolution of structure with composition

The quaternary systems Ca-N-Cl-Br and Ca-N-Br-I have been investigated resulting in the synthesis of a number of new layered nitride mixed halides. The evolution of structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques. A continuous solid solution exists between Ca₂NCl and Ca₂NBr with intermediate compounds adopting the same anti- α-NaFeO₂ structure (rhombohedral space group ) as the ternary end members. A phase transition occurs in the Ca₂NBr_1−yI_y system between y=0.7 and y=0.8 corresponding to a switch from cubic close packing to hexagonal close packing of metal-nitrogen layers and corresponding adoption of the anti-β-RbScO₂ (filled anti-CdI₂) structure (hexagonal space group P6₃/mmc). While nitride and halide anions occupy distinct crystallographic sites, there is no ordering of halides in quaternary materials irrespective of stoichiometry or structure type. All the nitride halides show temperature independent paramagnetic behaviour between 2 and 300 K.     

New deaminations IX - pyrolysis of N-alkyl-N,N-disulfonimides

N,N-Disulfonimide derivatives of certain alkyl amines stereoselectively pyrolyze without skeletal rearrangement to give up to 99% yields of alkenes.     

Perfluoroallyl fluorosulphonate

Perfluoroallyl fluorosulphonate, procured $\text{via}$ treatment of perfluoropropene with stabilized sulphur trioxide (‘Sulfan’), reacts with potassium iodide, potassium bromide, sodium methoxide, and phenylmagnesium bromide to yield the corresponding perfluoroallyl derivatives CF₂CFCF₂X, where X = I, Br, OMe, and Ph respectively.     

The valence shell spectra of acetylene and hydrogen excited by Zr Mζ x-rays. An example of the advantages provided by an ultra-soft x-ray source

Excitation of the valence shell molecular orbital spectrum of acetylene with Zr M_ζ (151.4 eV) radiation shows clearly all four expected bands 1π_u (11.4 eV), 3σ_g (16.8 eV), 2σ_u (18.8 eV) and 2σ_g (23.5 eV) with approximately equal intensity in contrast to He or Mg K_α excited spectra. A spectrum of molecular hydrogen can also be obtained with this radiation.     

The resurgence of Coulter counting for analyzing nanoscale objects

This review discusses recent advances in the science and technology of Coulter counting. The Coulter counting principle has been used to determine the size, concentration, and in favorable cases the surface charge, of nanometer-scale colloidal particles, viruses, DNA and other polymers, and metal ions. A resurgence of interest in the field of COulter counting is occurring because of the advent of new technologies that permit fabrication of membranes containing single, robust, and chemically well-defined channels having smaller and more uniform sizes than could be prepared in the past. These channels are prepared from biological materials, such as self-assembling membrane proteins, and from synthetic materials such as polymers, carbon nanotubes, and silicon-based inorganic materials. In addition to particle characterization, there have been a few recent examples of using Coulter counters to study chemical processes, such as the dehybridization of DNA.     

Echelle-spectrometer/image-dissector system for elemental quantitation by continuous-source atomic absorption spectrometry

The performance of an echelle-spectrometer/image-dissector system is evaluated for elemental quantitation by continuous-source atomic absorption spectrometry. Flame and graphite-furnace atomizers were used, as well as two different spectrometer configurations. Quantitative results obtained with the flame atomizer and a low-resolution spectrometer configuration are discussed briefly; results obtained with the graphite-furnace atomizer and a higher-resolution configuration are presented in detail. Absorption sensitivities for calcium (422.7 nm), chromium (425.4 and 357.9 nm), copper (324.8 nm), and manganese (403.1 and 279.5 nm) were all within a factor of 4–6 of comparable line- source absorption sensitivities, and calibration curves were linear up to absorbances of about 0.1. Further development of the system for simultaneous multi-element quantitation is discussed.     

Phosphine-catalyzed synthesis of 6-substituted 2-pyrones: manifestation of E/Z-isomerism in the zwitterionic intermediate

[reaction: see text] We report a one-step phosphine-catalyzed annulation between aldehydes and ethyl allenoate to form 6-substituted 2-pyrones. The mechanistic rationale for this reaction requires explicit discussion of the E/Z-isomerism of the zwitterionic intermediate formed by the addition of a phosphine to the allenoate. Sterically demanding trialkylphosphines facilitate the shift of equilibrium toward the E-isomeric zwitterion and lead to the formation of 6-substituted 2-pyrones. Various aromatic as well as aliphatic aldehydes undergo the transformation in moderate to excellent yield.     

Fine structure transition cross sections for several alkali + rare gas systems

The energy dependence, E_c.m. </ 0.2 eV, of the inelastic total cross sections for the ²P_{$\text{1}\text{2}$} → ²P_{$\text{3}\text{2}$} fine structure transition of the lowest excited states of the alkali atoms are calculated for the following systems: Na, K, Rb + He, Ne, Ar and Cs + He. Encouraging agreement between theory and experiment is obtained.     

Further studies on the pinacol coupling reaction

The pinacol coupling of R(+)3-methylcyclohexanone gives a product distribution $\text{dependent on the mode of coupling}$. Similar changes in product composition are also seen in the coupling of 4-methylcyclohexanone and in the mixed coupling of 3-methylcyclohexanone with cyclohexanone. In $\text{all cases studied}$, the [Al-Hg] method results in products having an axial methyl group. An X-ray structure of a product containing two axial methyl groups is presented.     

Stereoselective syn epoxidation of the dihydrodiols of dibenz[a,h] anthracene and 7-methylbenz[a] anthracene

Epoxidation of the bay region dihydrodiols of the title hydrocarbons affords stereoselectively the corresponding syn diol epoxides rather than the anticipated isomeric anti diol epoxides, indicative of a dominant cis-directing effect of the benzylic vs the allylic axial hydroxyl groups.