Relative electronegativities of germanium and silicon in organic compounds

Summary On the basis of a study of the relative reactivities of analogous carbofunctional compounds of germanium and silicon it is concluded that in these compounds germanium is more electronegative than silicon.We thank L. A. Leites for carrying out the spectroscopic analysis and A. A. Bugorkova for determining the kinetics of the reaction of (CH₃)₃GeCH₂Cl with KI.     

Synthesis of enantiomerically enriched tertiary 2-cyclohexene-1-thiols via configurationally stable alpha-thio-substituted allyllithium compounds

[reaction: see text] (S)-S-(2-Cyclohexenyl) N,N-diisopropylmonothiocarbamate [(-)-(S)-8] was deprotonated by sec-butyllithium/TMEDA to form a configurationally stable lithium compound (S)-9, which is the first example of a new class of alpha-thio-substituted organolithium compounds with improved properties. It is regioselectively alkylated by alkyl halides with complete stereoinversion to form the monothiocarbamates (+)-10 which afford highly enantioenriched tertiary 2-cyclohexene-1-thiols (+)-6 on reductive cleavage.     

Synthesis and properties of cyclic ethynyl compounds of silicon and germanium

Conclusions Five new ethynyl compounds of silicon and germanium were synthesized and subjected to thermal dehydropolycondensation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2149–2151, September, 1978.The authors express their gratitude to N. G. Komalenkova, T. L. Krasnova, and E. A. Chernyshev for supplying the halosilanes for the synthesis of compounds (IV) and (V).     

Organomagnesium synthesis of vinyl compounds of silicon,germanium and tin

Summary It was shown that condensation of Normant's reagent (CH₂=CHMgBr) with alkylchlorosilanes, -germanes, and -stannanes results in the synthesis of vinyl derivatives of silanes, germanes, and stannanes containing one, two, or three, vinyl radicals.     

Divalent silicon,germanium, and tin compounds with element--heteroatom bonds

Principal results and trends in chemistry of organic derivatives of divalent silicon, germanium, and tin containing bonds between these elements and the halogen, nitrogen, oxygen, and sulfur atoms are briefly surveyed. Selected characteristics of compounds with the element--phosphorus and element--arsenic bonds are discussed for comparison. Data on the synthesis and structures of new types of these compounds, viz., germanium(ii) diacylates, the alkoxy derivatives E¹⁴(OR)₂ and E¹⁴(OR)Y (E¹⁴ = Ge, Sn; R = Me₂NCH₂CH₂; Y = Cl, AcO, (Me₃Si)₂N), and the ate-complexes Li⁽⁺⁾[E¹⁴(OCH₂CH₂NMe₂)₃]^(–) and [Li(thf)₂]⁽⁺⁾[TsiE¹⁴(SBu)₂]^(–) (E¹⁴ = Ge, Sn; Tsi = (Me₃Si)₃C), are presented. It was established for the first time that germanium(ii) and tin(ii) derivatives can be stabilized in the monomeric form only through the intramolecular N_sp3E¹⁴ coordination bonds and the -acceptor effect of the oxygen atoms without introduction of bulky substituents.     

Proton magnetic resonance spectra of certain heteroorganic compounds of silicon and germanium

Conclusions A comparison of the PMR spectra of a number of saturated and unsaturated organic compounds of silicon and germanium shows that in the case of unsaturated compounds, an appreciable role is played by effects of d–p conjugation, which are stronger for silicon compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1312–1313, July, 1964     

SIMS for hydrogen quantification and structural analysis of amorphous silicon germanium compounds

Summary Hydrogen has been analysed quantitatively in a-Si_1–xGe_x:H alloys by SIMS with H variation from 1×10¹⁹ –1.3×10²² atoms/cm³ and x between 0 and 1. To quantify the absolute H concentration, SIMS measurements have been calibrated with nuclear reaction analysis, which exhibits excellent agreement with SIMS data for the total range of H and Ge variance. From abundances of the molecule ions SiH⁺ and GeH⁺ the fractions H bound to Si or Ge can be discerned and are in good accordance with quantification of SiH and GeH stretching modes in IR spectroscopic measurements. Preferential attachment of H to Si compared to Ge by a factor of 3.5 is determined for glow discharge a-SiGe:H samples; during annealing up to 900 K only small changes of this factor are observed.     

Recent developments in the chemistry of stable doubly bonded germanium compounds

During the last 10 years, several compounds of the type Ge=X (X = C, Ge, N, P, S) have been isolated as monomers. The stabilization of such derivatives, which are generally highly polymerizable, was achieved by using very bulky groups both on the germanium atom and on the heteroelement X. Conjugation (particularly in a few germenes and germaimines) and intramolecular or intermolecular coordination with oxygen or nitrogen, also contributes, in some cases, to the stabilization. The X-ray analyses of such compounds show a significant bond shortening of the double bond (8–10%) relative to the corresponding single bond and a planar or nearly planar germanium. These doubly bonded germanium derivatives are usually thermally stable but must be handled in an inert atmosphere because of their high sensitivity to oxygen and moisture; they are extremely reactive, much more than the corresponding carbon analogues. Nearly quantitative additions on the double bond have been observed with electrophiles and nucleophiles, and various types of cycloadditions also occur. Except in one case, a germylene behavior has not been observed, proving that such compounds retain their structural integrity in solution.     

PMR spectra of some five- and six-membered heterocyclic compounds of silicon and germanium

The PMR spectra of various 1-sila- and 1-germacyclopentanes and also those of some substituted disilacyclohexanes are discussed. The influence of the magnetic field of the aryl and vinyl substituents in 1,1-dialkyl-2,5-diaryl(vinyl)-1-sila(germa)cyclopentanes on the chemical shifts of the protons of the individual groups is studied, the differences found in the position of the PMR lines of the methyl and methylene groups showing the existence of cis-trans isomers in these heterocycles. With 1,1-dimethyl-2,5-divinylsilacyclopentane as an example, an increase in screening due to the magnetism of the multiple bonds for the protons of groups not directly connected with the unsaturated groupings and located in a direction perpendicular to the axis of the double bond has been found experimentally.Lecture at the XI-th Scientific Conference of the Institute of High-Molecular-Weight Compounds of the Academy of Sciences of the USSR (Leningrad, March, 1964) and at the All-Union Conference on the Use of Radiospectroscopy in Chemistry (Moscow, January, 1965).The authors express their gratitude to A. V. Kessenikh for taking several of the PMR spectra and for critical observations on the investigation.     

Comparative chemistry of isolable divalent compounds of silicon, germanium, and tin

Recent studies of the synthesis, structures, spectroscopic properties, and reactions of a series of isolable metallylenes (R2E:, E = Si (1), Ge (2), and Sn (3); R2 = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) are summarized. Because these group-14 metallylenes bear the same helmet-like ligand, a straightforward discussion of the element-dependence of the intrinsic properties of the group-14 element divalent compounds is possible. All these metallylenes were monomeric both in solution and in the solid state, indicating the effective steric protection by the ligand against dimerization. A small sigma-pi conjugation between C-Si(substituent) sigma orbitals and the vacant npz orbitals of divalent atoms in R2E: exists and the extent decreases in the order E = Si > Ge > Sn, as evidenced by UV-vis and NMR spectroscopies and X-ray crystallography. However, the extent of the sigma-pi conjugation in metallylenes 1-3 was much smaller than the electron-donating effects of neighboring nitrogen atoms in known stable cyclic diamino-substituted metallylenes, and hence metallylenes 1-3 are regarded as the least electronically perturbed. Comparative studies of the unique reactions among these metallylenes are also discussed.     

Application of enriched stable isotopes as tracers in biological systems: a critical review

The application of enriched stable isotopes of minerals and trace elements as tracers in biological systems is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation, primarily within inductively coupled plasma mass spectrometry (ICP-MS) instrumentation, such as reaction/collision cell ICP-MS and multicollector ICP-MS with improved isotope ratio measurement and interference removal capabilities. Adaptation and refinement of radioisotope tracer experiment methodologies for enriched stable isotope experiments, and the development of new methodologies coupled with more advanced compartmental and mathematical models for the distribution of elements in living organisms has enabled a broader use of enriched stable isotope experiments in the biological sciences. This review discusses the current and future uses of enriched stable isotope experiments in biological systems.     

Synthesis and application of new organometallic compounds of silicon and germanium in chemical radioprotection

Several organosilicon and organogermanium compounds possessing radioprotective activity have been synthesized. In this paper, we describe the preparation and study of the pharmacological properties of new organometallic compounds such as metallathiazolidines and metalladithioacetals derived from 1‐[N‐(2‐mercaptoethyl)‐­2‐aminoethyl] ‐ 2 ‐ (1‐naphthylmethyl) ‐2‐ imidazoline and 1‐[N‐(2‐mercaptopropyl)‐2‐aminoethyl]‐2‐(1‐naphthylmethyl)‐2‐imidazoline. We have noted a decrease in the toxicity and a rather important increase in the radioprotective activity of these new organometallic derivatives in comparison with the starting organic compounds. Copyright © 1999 John Wiley & Sons, Ltd.     

Production of stable isotopes at Urenco: 10 years of progress

In the last ten years, Urenco has built its spin-off activity of stable isotopes in a multi-million dollar business. It is a high quality, ISO certified, client oriented and profitable European business with further growth potential.     

Determination of volatile organic compounds from truffles via SPME-GC-MS

Volatile organic compounds (VOCs) of nine Tuber species and two corresponding forms are identified via solid-phase microextraction-gas chromatography-mass spectrometry analysis. Seventy-five compounds are identified. The most abundant are dimethylsulphide, 2- and 3-methylbutanal, 2-methylpropanol, and butanone.     

Reactivity of silicon and germanium doped CNTs toward aromatic sulfur compounds: A theoretical approach

Adsorption processes of thiophene and benzothiophene on pristine carbon nanotubes (CNTs), and on CNTs doped with Si or Ge, have been modeled with Density Functional. This is the first study on the chemical reactivity of such doped tubes. The calculated data suggest that the presence of silicon or germanium atoms in CNTs increases their reactivity toward thiophene, and benzothiophene. The adsorption of these species on pristine CNTs seems very unlikely to occur, while the addition products involving doped CNTs were found to be very stable, with respect to the isolated reactants, in terms of Gibbs free energy. Several of these adsorption processes were found to be significantly exergonic (ΔG < 0) in non-polar liquid phase. The results reported in this work suggest that Si and Ge defects on CNTs increase their reactivity toward unsaturated species, and could make them useful in the removal processes of aromatic sulfur compounds from oil-hydrocarbons. However, according to our results, CNTs doped with Si atoms are expected to be more efficient as aromatic sulfur compounds scavengers than those doped with Ge. These results also suggest that the presence of silicon and germanium atoms in the CNTs structures enhances their reactivity toward nucleophilic molecules, compared to pristine carbon nanotubes.