Hydrides mass spectroscopy

Since 1965 we have found an unexpected number of binary phosphorus hydrogen compounds in addition to the well-known hydrides PH and 2H4 (Table I). These phosphanes have been detected in the hydrolysis products of calcium phosphide or in the thermolysis products of 2H4 mass spectroscopy. Only the compounds... 

Fast atom bombardment mass spectroscopy has proved to be most useful when applied to the characterization of heteronuclear gold cluster compounds containing hydride ligands (137,149,155). Characterization is aided by the observation that peaks are invariably present in the spectrum corresponding to ions that contain all of the hydride... 

For ICP-OES-MS (inductively coupled plasma-optical emission spectroscopy-mass spectroscopy) work, the desolvator will remove oxide and hydride polyatomic ion interferences, i.e. ArO+ is reduced 100 fold, which allows for improved detection of Fe. The solvent loading reduction is caused by volatiles passing through the walls of a tubular microporous Teflon PTFE membrane. The argon gas removes the solvent vapour from the exterior of the membrane. Solvent-free analytes remain inside the membrane and are carried to the plasma for atomisation and excitation. 

A different stereochemical outcome is observed in the reduction of the tetracyclic indanone derivative using lithium aluminum hydride in diethyl ether to afford the rranx-alcohol (83 %)212 or the cw-alcohol in the Meerwein-Ponndorf-Verley reduction employing aluminum isopropox-ide and isopropanol (99% 212 83 %213). The stereochemistry of the products were confirmed by mass spectroscopy giving a high M+-water peak (.vyn-climination) in the case of the c/.v-al-cohol213. 

The new alkaloid chamaetine (1), isolated from Chamaecytisus species, is an epimer of nuttaline (1 with -OH group). The structure of chamaetine was established by n.m.r. and mass spectroscopy and by conversion of the alkaloid into sparteine and into lupanine. Reduction of chamaetine with lithium aluminium hydride gave an amorphous desoxy derivative, which was shown to be identical with 4-a-hydroxysparteine by a comparison of azo-esters. 

The best methods for investigation of hydride complexes are IR, NMR, and mass spectroscopy. The v(M —H) bands for terminal hydrogen atoms occur in the range 1700-2300 cm The bridging H atoms connected to two or more metal atoms have their frequencies at 800-1550 cm However, the identification of metal hydrides based on IR spectra is not reliable because the intensity of the v(M —H) bands changes considerably and other bands such as v(CO), v(CN), v(C = C), and v(N = N) are present in the M —H range. In some metal hydrides, the v(M —H) band was not even observed. 

Bridging hydride ligands are usually more firmly bound than their terminal counterparts, and are readily characterized by spectroscopic methods such as NMR and mass spectroscopy. Application of the NMR spectroscopy is sometimes difficult because of low solubility and... 

Carbonyl hydride clusters are moderately volatile and subjected to mass spectroscopy. Whereas terminal hydride ligands are frequently lost upon ionization, bridging hydride ligands are tenaciously retained. Therefore, mass spectroscopy is useful in distinguishing between terminal and bridging hydride ligands. 

This experiment describes a fixed-size simplex optimization of a system involving four factors. The goal of the optimization is to maximize the absorbance of As by hydride generation atomic absorption spectroscopy using the concentration of HCl, the N2 flow rate, the mass of NaBH4, and reaction time as factors. 

Numerous methods have been pubUshed for the determination of trace amounts of tellurium (33—42). Instmmental analytical methods (qv) used to determine trace amounts of tellurium include atomic absorption spectrometry, flame, graphite furnace, and hydride generation inductively coupled argon plasma optical emission spectrometry inductively coupled plasma mass spectrometry neutron activation analysis and spectrophotometry (see Mass spectrometry Spectroscopy, optical). Other instmmental methods include polarography, potentiometry, emission spectroscopy, x-ray diffraction, and x-ray fluorescence. 

We do not know exactly where the hydrogen binds at the active site. We would not expect it to be detectable by X-ray diffraction, even at 0.1 nm resolution. EPR (Van der Zwaan et al. 1985), ENDOR (Fan et al. 1991b) and electron spin-echo envelope modulation (ESEEM) (Chapman et al. 1988) spectroscopy have detected hyperfine interactions with exchangeable hydrous in the NiC state of the [NiFe] hydrogenase, but have not so far located the hydron. It could bind to one or both metal ions, either as a hydride or H2 complex. Transition-metal chemistry provides many examples of hydrides and H2 complexes (see, for example. Bender et al. 1997). These are mostly with higher-mass elements such as osmium or ruthenium, but iron can form them too. In order to stabilize the compounds, carbonyl and phosphine ligands are commonly used (Section 6). 

The spectroscopic methods chosen to characterize a particular compound will depend on the character of that compound as well as the type of information to be gained. For example, neutral clusters are readily characterized by mass spectrometry, whereas this method has been of little use for characterizing anionic clusters. Likewise, the subject of interest is the location of a hydride ligand or the site of phosphine or phosphite substitution, the most versatile tools are NMR spectroscopy and X-ray diffraction. We cannot discuss all the common characterization techniques in detail, but we shall highlight a few of the more important features. 

Fast atom bombardment mass spectrometry and NMR spectroscopy have been used to confirm that both clusters possess two hydride ligands, but these could not be located in the X-ray analyses and are... 

For the first time the possibility of the use of metal (La, Y) hydrides to prepare composite graphite electrodes was studied. The yield of DCB extracts of C2n/M C82 (M = Y, La, Ce, Gd) from soot obtained by evaporation of composite electrodes based on YH3, LaH3, CeH3 or GdH3 is 2-3 % higher (4-5 wt. % of the primary soot) than the yield of the extracts from soot synthesized using the electrodes based on metallic yttrium, lanthanum, cerium or gadolinium. EMF.v Y2 C84 and Ce2 C78 were produced, separated, and isolated for the first time. Their purity was justified by S8-MALDI mass spectrometry and they were characterized by UV-Vis-NIR absorption spectroscopy. 

D. Sanchez-Rodas, A. Geiszinger, J. L. Gomez-Ariza, K. A. Francesconi, Determination of an arsenosugar in oyster extracts by liquid chromatography electrospray mass spectrometry and liquid chromatography-ultraviolet photooxidation-hydride generation atomic fluorescence spectroscopy, Analyst, 127 (2002), 60-65. 

When a bulky bis(adamantylethoxy) imidazolium salt was treated with potassium hydride the reaction did not afford the expected potassium-carbene.18 Instead, elimination of one alcohol arm produced a mono (adamantylethoxy) imidazole (9) (Scheme 5). Treatment of this with isopropyl iodide resulted in the alcohol imidazolium iodide salt, which undergoes deprotonation with lithium hexamethyldisilazide to afford the lithium alkoxy carbene (10) which was characterised by mass spectrometry and multinuclear NMR spectroscopy. The C2 carbon in 10 resonates at 186.3 ppm in the 13C NMR spectrum, which is a significantly lower frequency than the similar ligand in 7 which has lithium iodide incorporated into the structure. 

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