摘要:

Examples from different fields have been collected to demonstrate the unique properties of the pentamethylcyclopentadienyl (cp*) ligand in main-group chemistry. First, compounds with σ-bonded cp* ligands are thermally very stable and, therefore, allow detailed investigations of their temperature-dependent dynamic behavior. Drastic differences in the rates of 1,5-sigmatropic rearrangements are observed; the comparison of experimental results with theoretical calculations is very useful in understanding basic principles of fluxionality. Second, the polyhaptobonded cp* ligand stabilizes π-complexes with main-group elements as central atoms. Using isolobal and isoelectronic relationships, these π-complexes can be organized in four structurally different classes. Furthermore, the cp* ligand is sterically demanding in boron, silicon, phosphorus, and sulfur compounds, leading to kinetically stabilized species and rendering nucleophilic substitution reactions more difficult. Finally, the cp* ligand is a good leaving group; cp*-element bonds can be split by nucleophilic, electrophilic and reducing agents, thus allowing an interesting substitution chemistry.

ISSN:0260-3594    

DOI:10.1080/02603598708072286

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Mass spectrometry is an extremely sensitive method for the determination of elements down to the sub-pg level. The different ionization methods used for mono-and multi-element analyses are discussed. Spark source mass spectrometry has been the most commonly multi-element technique in the past. However, inductively coupled plasma and glow-discharge mass spectrometry will probably replace spark source mass spectrometry in the future. Accurate trace element determinations can only be obtained with isotope dilution mass spectrometry. Because of a lack of accurate methods, isotope dilution is one of the few definitive calibration techniques that can be used for trace element analyses. The formation of negative and positive thermal ions on a hot metal surface is the most frequently applied ionization method in isotope dilution mass spectrometry. All elements which can be analyzed by this method are listed. A selected number of trace determinations with thermal ionization isotope dilution mass spectrometry are discussed, e.g. the analysis of ultra-low amounts of heavy metals in Antarctic snow, of halide traces in geochemical materials, and of nitrite and nitrate in food samples. Determinations of element species with the isotope dilution technique will become more and more important in the future.

ISSN:0260-3594    

DOI:10.1080/02603598708072287

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0260-3594    

DOI:10.1080/02603598708072285

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor