Spectroscopy oxides

Mossbauer spectroscopy Oxidation and spin states of the metal in the prosthetic group. Electronic structure and spatial arrangement of the active centre 124,125)... 

Fritsch and Weingarten 386 have studied the electrooxidation of 22 substituted enamines by cyclic voltammetry and ESR spectroscopy. Oxidation potentials of these strong electron donors may be as low as -0,901 V (vs.S.C.E.). The life times of the initially formed radical cations range from 0,005 sec to days depending on the efficiency of reactive site blocking or stabilization by substituents. Coupling constants from the ESR spectra indicate that the unpaired electron is polarized away from the dimethylamino substituents. The opposite is true for the... 

Cyclization of enone (9) in hexane with boron trifluorideetherate in presence of 1,2-ethanedithiol, followed by hydrolysis with mercury (II) chloride in acetonitrile, yielded the cis-isomer (10) (16%) and transisomer (11) (28%). Reduction of (10) with lithium aluminium hydride in tetrahydrofuran followed by acetylation with acetic anhydride and pyridine gave two epimeric acetates (12) (32%) and (13) (52%) whose configuration was determined by NMR spectroscopy. Oxidation of (12) with Jones reagent afforded ketone (14) which was converted to the a, 3-unsaturated ketone (15) by bromination with pyridinium tribromide in dichloromethane followed by dehydrobromination with lithium carbonate and lithium bromide in dimethylformamide. Ketone (15), on catalytic hydrogenation with Pd-C in the presence of perchloric acid, produced compound (16) (72%) and (14) (17%). The compound (16) was converted to alcohol (17) by reduction with lithium aluminium hydride. 

Interestingly, 2-phenylpteridine behaves differently. At —40°C the 1 1 adduct is formed, while at — 60 °C two adducts are present in the solution. One is the C-4 monoadduct, the other one is the 2 1 C-6/C-7 diadduct, as is proven by NMR spectroscopy. Oxidation of the mixture of the two adducts only gave 4-amino-2-phenylpteridine. Apparently the oxidation rate of the 1 1 adduct at C-4 is faster than the oxidation of the 2 1 diadduct, shifting the equilibrium between both adducts to the C-4 adduct. So the rate of the oxidation determines the ratio of the products obtained. 

The catalysts H3PMoi204o,H3 PW12O40 and H5PV2M010O40 were prepared according to the procedure reported in literature [6] and characterized using IR,UV and P nmr spectroscopy. Oxidation of alkylbenzene was carried out at 303 K for 3 hours with acetonitrile as solvent. Hydrogen peroxide to substrate ratio of 2.5 mol was used in these... 

The mechanism of the related palladium-catalyzed asymmetric hydrocyanation of alkenes has also been examined in detail using [Pd(RR-diop)(C2H4)] and related chiral species as precursor complexes. These additions gave the exo nitrile product with up to 40% enantiomeric excess, indicating stereoselective complexa-tion of norbornene to the Pd(0) via the exo face. The plausible reaction intermediates [Pd(diop)(norbornene)] and the hydrido cyanide (60) were characterized by and P NMR spectroscopy. Oxidative addition of HCN to Pd(0) is believed to precede rate-determining alkene binding. 

The hydrophilicity of nanooxides, which plays a very important role in their applications and affects many of their properties, was analyzed using calorimetry (oxides were degassed at 473 K at low pressures for several hours) and H NMR spectroscopy (oxides were equilibrated in air) methods applied to samples after different pretreatments. This characteristic is linked to the possibility of the formation of strong hydrogen and donor-acceptor bonds or/and dissociative adsorption of water. The treatments before the calorimetric measurements resulted in desorption of intact water and a portion of dissociatively adsorbed water (=MOH, M 0(H)M"=, where M=Si, Al, or Ti) from both surface and volume of oxide nanoparticles. However, in the case of the NMR measuranents, surface and volume water was readsorbed from air. Therefore, one could expect that the heat effects on the adsorption of water on the calorimetric measuranents should be stronger than that on the NMR measurements. This is typically observed for the samples studied with the exception of SA8 and ST20 (Table 2.12). 

Marken, F., R. D. Webster, S. D. Bull, and S. G. Davies, Redox processes in microdroplets studied by voltammetry, microscopy, and ESR spectroscopy oxidation of N,N,N, N -tetrahexylphenylene diamine deposited on solid electrode surfaces and immersed in aqueous electrolyte solution, J Electroanal Chem, Vol. 437, (1997) p. 209. 

FT IK-PAS can also be used as a rapid and nondestructive technique for quantitative characterization of the surface degradation of aged polymers and other compounds. Using FTIR-PAS spectroscopy, oxidation profiles of the various photooxidized polyisoprene-polystyrene copolymers have been investigated. 

As previously reported, oxidation products of hydroxylaminodinitrotoluene could be extracted from the reaction mixture azoxytetranitrotoluene (32) and TNT (6) were identified by chromatographic techniques and UV absorption spectroscopy. Oxidation of hydroxylaminodinitrotoluene occurred only if lignin peroxidase, H2O2, and veratryl alcohol were present in the test mixture. Hydroxylaminodinitrotoluene alone is, therefore, a poor substrate for the lignin peroxidase and veratryl alcohol is necessary for its oxidation. But hydroxylamino-... 

Experimentally, almost the only approach towards a characterization of high-surface-area oxides is the use of surface probes (e.g., adsorption of probe molecules) and their spectroscopy. Oxide surfaces are usually terminated by OH groups unless they are treated at elevated... 

Edg] DSC, XRD, EPMA, TEM, Mossbauer spectroscopy Oxidation of NdFeB magnets... 

XPS X-ray photoelectron spectroscopy [131-137] Monoenergetic x-rays eject electrons from various atomic levels the electron energy spectrum is measured Surface composition, oxidation state... 

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

As with any system, there are complications in the details. The CO sticking probability is high and constant until a 0 of about 0.5, but then drops rapidly [306a]. Practical catalysts often consist of nanometer size particles supported on an oxide such as alumina or silica. Different crystal facets behave differently and RAIRS spectroscopy reveals that CO may adsorb with various kinds of bonding and on various kinds of sites (three-fold hollow, bridging, linear) [307]. See Ref 309 for a discussion of some debates on the matter. In the case of Pd crystallites on a-Al203, it is proposed that CO impinging on the support... 

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is described in section Bl.25,2.1. The most connnonly employed x-rays are the Mg Ka (1253.6 eV) and the A1 Ka (1486.6 eV) lines, which are produced from a standard x-ray tube. Peaks are seen in XPS spectra that correspond to the bound core-level electrons in the material. The intensity of each peak is proportional to the abundance of the emitting atoms in the near-surface region, while the precise binding energy of each peak depends on the chemical oxidation state and local enviromnent of the emitting atoms. The Perkin-Elmer XPS handbook contains sample spectra of each element and bindmg energies for certain compounds [58]. 

In addition to the many applications of SERS, Raman spectroscopy is, in general, a usefiil analytical tool having many applications in surface science. One interesting example is that of carbon surfaces which do not support SERS. Raman spectroscopy of carbon surfaces provides insight into two important aspects. First, Raman spectral features correlate with the electrochemical reactivity of carbon surfaces this allows one to study surface oxidation [155]. Second, Raman spectroscopy can probe species at carbon surfaces which may account for the highly variable behaviour of carbon materials [155]. Another application to surfaces is the use... 

Qin L, Tripathi G N R and Schuler R H 1987 Radiolytic oxidation of 1,2,4-benzenetriol an application of time-resolved resonance Raman spectroscopy to kinetic studies of reaction intermediates J. Chem. Phys. 

Dadap J I, Hu X F, Anderson M H, Downer M C, Lowell J Kand Aktsiperov O A 1996 Optical second-harmonic electroreflectance spectroscopy of a Si(OOOI) metal-oxide-semiconductor structure Phys. Rev. B 53 R7607-9... 

Figure Bl.22.4. Differential IR absorption spectra from a metal-oxide silicon field-effect transistor (MOSFET) as a fiinction of gate voltage (or inversion layer density, n, which is the parameter reported in the figure). Clear peaks are seen in these spectra for the 0-1, 0-2 and 0-3 inter-electric-field subband transitions that develop for charge carriers when confined to a narrow (<100 A) region near the oxide-semiconductor interface. The inset shows a schematic representation of the attenuated total reflection (ATR) arrangement used in these experiments. These data provide an example of the use of ATR IR spectroscopy for the probing of electronic states in semiconductor surfaces [44]-...

XPS X-ray photoelectron spectroscopy Absorption of a photon by an atom, followed by the ejection of a core or valence electron with a characteristic binding energy. Composition, oxidation state, dispersion... 

Wang L S 2000 Photodetachment photoelectron spectroscopy of transition metal oxide species Photoionization and Photodetaohment Advanced Series in Physical Chemistry 10, ed C Y Ng (Singapore World Scientific)... 

In voltammetry a time-dependent potential is applied to an electrochemical cell, and the current flowing through the cell is measured as a function of that potential. A plot of current as a function of applied potential is called a voltammogram and is the electrochemical equivalent of a spectrum in spectroscopy, providing quantitative and qualitative information about the species involved in the oxidation or reduction reaction.The earliest voltammetric technique to be introduced was polarography, which was developed by Jaroslav Heyrovsky... 

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