Periodic ab initio calculation of nuclear quadrupole parameters as an assignment tool in solid-state NMR spectroscopy: applications to 23Na NMR spectra of crystalline materials

Periodic ab initio HF calculations using the CRYSTAL code have been used to calculate (23)Na NMR quadrupole parameters for a wide range of crystalline sodium compounds including Na(3)OCl. An approach is developed that can be used routinely as an alternative to point-charge modelling schemes for the assignment of distinct lines in (23)Na NMR spectra to specific crystallographic sodium sites. The calculations are based on standard 3-21 G and 6-21 G molecular basis sets and in each case the same modified basis set for sodium is used for all compounds. The general approach is extendable to other quadrupolar nuclei. For the 3-21 G calculations a 1:1 linear correlation between experimental and calculated values of C(Q)((23)Na) is obtained. The 6-21 G calculations, including the addition of d-polarisation functions, give better accuracy in the calculation of eta((23)Na). The sensitivity of eta((23)Na) to hydrogen atom location is shown to be useful in testing the reported hydrogen-bonded structure of Na(2)HPO(4).     

Carbon isotopomers measurement using mid-IR tunable laser sources

Recent developments of two mid-infrared tunable laser spectrometers dedicated to carbon isotope ratio determination are presented. First, a field deployable quantum cascade laser-based sensor is described, along with line selection strategy for (13/12)CO(2) ratio measurements. Secondly, an instrument architecture based on difference frequency generation is presented. The analyses of fundamental limitations, specifically temperature and pressure stability, and water vapor collision broadening, are detailed.     

Formal radical cyclization onto benzene rings--a general method proceeding via cross-conjugated dienones

Cross-conjugated dienones of type 5 (X = I), which are readily available from phenols, undergo radical cyclization (5 --> 6 --> 7), and the products are easily aromatized (7 --> 8), giving substances that are formally derived by radical cyclization onto a benzene ring (cf. eqn. (1)).     

H NMR Measurements of Wet/Dry Ratio andT1,T2Distributions in Lung

Proton-magnetic-resonance measurements have been carried out on juvenile porcine peripheral lung parenchyma. The free-induction-decay signal contained a motionally restricted component which decayed in a few tens of microseconds and a mobile component with aT₂time greater than 1 ms. The average second moment,M₂, for the motionally restricted signal was found to be 3.42 ± (0.25) × 10⁹s⁻². TheT₂distribution for the mobile signal consistently showed four resolvable components ofT₂range: 2–6, 10–40, 80–110, and 190–400 ms. The 2–6 ms component was present in a fully dehydrated preparation and was therefore assigned to a nonaqueous lung constituent. The motionally restricted FID component had aT₁= 0.772 ± 0.11 s and the mobile component had aT₁= 0.967 ± 0.02 s. The hydrogen content per unit mass for lung parenchyma and water were estimated in two ways: (1) on the basis of chemical content and (2) on the basis of comparison of restricted and mobile signals to the gravimetric (G) water content for a lung sample studied at a wide range of water contents. Lung wet/dry weight ratios were estimated from the free-induction decays and compared with gravimetric measurement. The ratio of (wet/dry)_NMR/(wet/dry)_Gwas 1.00 ± 0.08 and 1.00 ± 0.05 for the two methods of estimation.     

Determination of boron and lithium in diverse biological matrices using neutron activation-mass spectrometry (NA-MS)

Summary Essential features of the neutron activation-mass Spectrometry (NA-MS) technique are described. Applicability of this technique for the simultaneous determination of boron and lithium is demonstrated for a diverse group of biomaterials. NA-MS is a nondestructive analytical technique, and dynamic in nature since its coverage extends to a broad range of concentration levels. Contamination after the irradiation step, extraneous by natural lithium or boron is inconsequential, since only the activation products are the analyted assayed. Coupling the nuclear activation phenomenon which generates ⁴He and ³He (from ¹⁰B and ⁶Li, respectively), with the high precision potential of mass spectrometry forms the bases of this technique. Under ideal conditions the detection limit is extendable to pg g^–1 concentration ranges and therefore, it is extremely well suited to investigate the natural concentration levels of boron and lithium in biomaterials. The potential of this method for the determination of lithium in biomedical trace element research is of special significance since determination of sub-ppb levels of lithium by other analytical techniques faces serious analytical difficulties mainly due to contamination control and in some cases to insufficiently low detection limits.     

19F coupling constants and chemical shifts in some dimethylamino and alkoxy derivatives of tellurium hexafluoride,cis TeF4XY

The spectra of A₂BC spin systems provided by the ¹⁹F nuclei in cis (RO) (MeO)TeF₄ and (RO) (Me₂N)TeF₄ (R = Me, Et, Pr, i-Pr) have been recorded and analysed. The geminal coupling constants ²J(F,F) range from 137–174 Hz and trends in the ¹⁹F chemical shifts permit complete assignment of the resonances. Stereospecific coupling between ¹⁹F and the protons of the N-methylamino groups is also observed.     

Corporate manpower planning: a review of models

Manpower planning has achieved maturity during the past decade. Personnel practitioners have become conversant with the analysis of manpower systems, the use of quantitative techniques, and have developed a sound approach to the whole question of manpower management. But, whilst they no longer rely on the management scientist for using those models and other techniques now widely available, there is a continued contribution to be made in advancing the field. This paper reviews the practical relecance of existing models. It concentrates on techniques for evaluating manpower supply and career management problems, distinguishing especially between the roles played by exploratory and normative models. The author hopes that this article will give management scientists a realistic appraisal of current practice and provide pointers as to where developments are most needed.     

Interaction of hexafluoroacetone and hexafluoroisopropylidenimine with some organosilicon- and organotin- amines,azides and phosphinimines

Metathetical and insertion reactions of perhalogenoketones and hexafluoroisopropylidenimine with organosilicon and organotin phosphinimines, dimethylaminotrimethyltin and trimethylsilyl azide are reported. Activation energies for nitrogen inversion in some of the organometallic ketimines produced have been determined.