Chemie der Phosphorfluoride. XXXIX. Synthese und Untersuchung der Temperaturabhängigkeit der kernmagnetischen Resonanzspektren von Hexafluorisopropylideniminofluorphosphoranen und Fluorphosphin-Bis(Trifluormethyl)hexafluorisopropylideniminomethylimiden

Chemistry of Phosphorus Fluorides. XXXIX. Synthesis and Investigation of the Dependence of Temperature of the NMR Spectra of Hexafluoroisopropylidence Iminofluorophoranes and Fluorophosphin-Bis(Trifluormethy)hexafluroisopropylidene Imnomethylimides. The title compounds were obtained by the reaction of the lithium salt of hexafluoroisopropylimine with fluorophosphoranes, R_nPF_5?n (n = 0, 1; R = hydrocarbon group). ¹⁹F variable temperature n.m.r. spectra show intermediate rate of intramolecular exchange at phosphorus but apparent fast “isomerisation” at nitrogen. The fluorophosphine imides, on the other hand, show intermediate rates of “isomerisation” at nitrogen in the hexafluoroisopropylidene moiety.     

Collisional activation spectra of field ionised molecules

The collision of field ionised molecular ions of high kinetic energy (8 keV) with neutral target atoms (helium) gives rise to a large variety of fragments. In general the types of fragments, as well as their abundance ratios, closely resemble those formed under 70 eV electron-impact. The differences observed between the collisional activation spectra of several field ionised[C₇H₈]+. ions, as well as the differences observed between several [C₈H₈]+. ions can be rationalised assuming different degrees of isomerisation. The usefulness of collisional fragmentation spectra for structure determination of organic compounds has been demonstrated for a variety of compounds and some mixtures.     

1H NMR spectra of E and Z pyridine-2-carbaldehyde 2′-pyridylhydrazone and related compounds

Proton magnetic resonance spectra at 100 MHz are reported for the E- and Z-isomers of pyridine-2-carbaldehyd 2′- pyridylhydrazone in carbon tetrachloride, d₆-dimethylsulphoxide and d₆-benzene solutions, and for various monomethylated derivatives in d₆-dimethylsulphoxide. The spectral parameters obtained by analysis with the help of LAOCOON 3 are discussed in terms of solvent effects and the chemical shift changes consequent upon isomerisation are evaluated. Some conclusions are reached concerning the preferred conformations of the E- and Z-isomers of pyridine-2-carbaldehyde 2′-pyridylhydrazone.     

The thermal isomerisation of some four co-ordinate square planar complexes of palladium and platinum with phosphine ligands

Thermally induced cis—trans isomerisation is reported for square planar complexes of the type MX₂L₂, M = Pd or Pt, L = organophosphorus ligand and X = halide. However, the palladium dichloro-phenyldimethyl complex provides another example of the more unusual trans—cis isomerisation. A number of phosphine complexes of platinum have been vacuum-distilled, in some cases with accompanying isomerisation. The tendency for such isomeric behaviour is interpreted in terms of variation in metal to phosphorus bond strength.     

Electron-impact-induced rearrangements of organic ions VIUnimolecular reactions of isomeric[C8H9]+ions

Metastable ion spectra and deuterium labelling have been used to investigate a series of gaseous [C₈H₉]+ ions of isomeric structures. The similarity of the intensities of their metastable loss of hydrogen, acetylene and ethylene molecules and metastable reactions of specifically labelled ions, suggests that the [C₈H₉]+ reacting ions, formed initially with different structures, isomerise to a common structure or mixture of structures via deep-seated rearrangement reactions which render all hydrogen atoms equivalent. The isomerisation process involved is controlled by a conversion of a vinyl bond into an allyl-type bond, thus destroying the aromatic moiety.     

Ionisation potentials in structure analysis of isomeric nitrones,oxaziranes, O-ether oximes and acid amides

Comparative studies of the ionisation potentials and the mass spectra of some isomeric nitrones, oxaziranes, O-ether oximes and acid amides gave no evidence for hermally-induced isomerisation in the mass spectrometer. Characteristic differences in the electron-impact-induced fragmentation patterns are discussed.     

Lewis acid-catalysed isomerisation of thionolactones to thiolactones: inversion of configuration

Boron trifluoride and indium(III) trifluoromethanesulfonate were found to efficiently catalyse the isomerisation of thionolactones to thiolactones in good yields. When applied to an optically active γ-thionolactone, the isomerisation reaction proceeded with a complete inversion of configuration by using BF₃·Et₂O.     

Indenyl and fluorenyl transition metal complexes IX. A study of the reversible isomerisation of η6- and η5-fluorenylchromium tricarbonyl anions by 13C NMR spectroscopy

¹³C NMR spectroscopy was used to study the reversible isomerisation of η⁶- and η₅-fluorenylchromium tricarbonyl anions. The influence of the electron withdrawing effect of the Cr(CO)₃ moiety on the π-electron distribution has been examined in the uncoordinated rings of η⁶-(I), η⁵-(II) fluorenylchromium tricarbonyl anions and fluorenylchromium tricarbonyl (III). IR spectra of I-M⁺ (M = Li, Na, K, Rb, Cs, Ph₃PCH₃) is discussed in connection with the structure of ion pairs in these salts.     

Physical and chemical properties of hydroxyflavones. V. Deuteroxyflavones from acetoxyflavones by imidazole-catalyzed deacetylation

A recently described procedure for imidazole-catalyzed deacetylation of acetoxyflavones has been modified by effecting hydrolysis in a mixture of deuterium oxide and deuterioethanol (C₂H₅OD), or in deuterium oxide and deuteriomethanol (CH₃OD). Application of the new procedure to monoacetoxyflavones has resulted in the monodeuteroxyflavone. 5-Deuteroxyflavone has been obtained also by hydrolysis of a rubidium salt in deuterium oxide. Imidazole-catalyzed hydrolysis of four diacetoxyflavones in a mixture of deuteriomethanol and deuterium oxide is described. Infrared spectral data are presented for the deuteration products, with emphasis on OD stretching and vibrational modes. Comparison of spectra of appropriate monohydroxyflavones and monodeuteroxyflavones permits assignment of δ (OH) bands in four hydroxyflavone spectra.     

Surface Properties of Impregnated Mixed Oxide Catalysts

The results of a comparative study of nickel oxide-alumina and nickel oxide-silica alumina catalysts in the light of the characteristics of the support systems alumina and silica-alumina are presented. The impregnation of NiO does not produce any significant change in the textural characteristics like surface area and pore volume of the support oxides. However the deposited nickel oxide leads to the modification of the surface acidity determined by Hammett indicators. In the case of parent oxides the ammonia adsorption is strong (from heat of adsorption measurement) for alumina and silica-alumina, though for the former it is slightly stronger at comparable surface coverages. But the adsorption of ammonia on NiO? Al₂O₃ is weak while it is strong on NiO/SiO₂? Al₂O₃ at the same comparable surface coverages. The reduction in acidity is reflected in the poor dehydration and absence of skeletal isomerisation on NiO impregnated catalysts.     

Geometric Isomerisation of Bifunctional Alkenyl Fluoride Linchpins: Stereodivergence in Amide and Polyene Bioisostere Synthesis

Amide groups are pervasive across the chemical space continuum, where their structural and pharmacological importance, juxtaposed with the hydrolytic vulnerabilities, continues to fuel bioisostere development. Alkenyl fluorides have a venerable history as effective mimics (Ψ[CF=CH]) owing to the planarity of the motif and intrinsic polarity of the C(sp²)−F bond. However, emulating the s-cis to the s-trans isomerisation of a peptide bond with fluoro-alkene surrogates remains challenging, and current synthetic solutions only enable access to a single configuration. Through the design of an ambiphilic linchpin based on a fluorinated β-borylacrylate, it has been possible to leverage energy transfer catalysis to affect this unprecedented isomerisation process: this provides geometrically-programmable building blocks that can be functionalised at either terminus. Irradiation at λ_max=402 nm with inexpensive thioxanthone as a photocatalyst enables rapid, effective isomerisation of tri- and tetra-substituted species (up to E/Z 98 : 2 in 1 h), providing a stereodivergent platform for small molecule amide and polyene isostere discovery. Application of the methodology in target synthesis and initial laser spectroscopic studies are disclosed together with crystallographic analyses of representative products.     

Use of QUASES™/XPS measurements to determine the oxide composition and thickness on an iron substrate

QUASES? Analyze and Generate were used to model the extrinsic loss structures for XPS spectra of oxide films grown on iron in such a way that their thickness and structure could be determined. The Generate program used in conjunction with spectra of model iron oxides allowed for both magnetite (Fe₃O₄) and maghaemite (γ‐Fe₂O₃) structures to be identified in all films studied. These structures were identified as overlying layers in the oxide films and were usually intermixed at their interface. The absence of other iron oxide structures within the film could be tested based on their goodness of fit to the experimental spectrum. Comparison of the thickness values obtained using Generate with those found using nuclear reaction analysis suggested that the Generate results were higher by 20%. This difference likely resulted from the use of a calculated inelastic mean free path value for Fe 2p electrons in the Generate calculation rather than using the real attenuation length. For oxide films whose thickness approached 10 nm, the QUASES? results for photoelectron spectra obtained with a Zr achromatic x‐ray source were compared with those from the standard Al monochromatic source. In this particular case, the oxide thicknesses obtained using Generate and Analyze were found to be more consistent when the Zr source was used. Copyright © 2004 John Wiley & Sons, Ltd.     

On the mechanism of intramolecular nitrogen‐atom hopping in the carbon chain of C6N radical: A Plausible 3c−4e crossover Long‐Bond

Linear isomers of C₆N radical differ in the position of the nitrogen atom in the carbon chain of C₆N. Reaction routes, involving intramolecular nitrogen atom insertion at varying position in the carbon chain of C₆N, are analyzed for the isomerisation between linear isomers of C₆N. Through an automated and systematic search performed with global reaction route mapping of the potential energy surface, thermal isomerisation pathways for C₆N radical are proposed based on the computations carried out at CASSCF/aug‐cc‐pVTZ, and CCSD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) levels of the theory. Notably, a high lying linear isomer, centrosymmetric with respect to the nitrogen atom, is observed to be stabilized by a unique crossover three center‐four electron π long bond between the carbon atoms that are spatially separated by a nitrogen atom in a natural bond orbital. This long bond is concluded to be responsible for the predicted thermal isomerisation to be more feasible than the dissociation during the isomerisation pathway of a linear isomer of C₆N. © 2014 Wiley Periodicals, Inc.     

Die identifizierung und untersuchung von isomeren O-acylribonucleosiden mit hilfe des circulardichroismus

The CD spectra of benzoyl, p-nitrobenzoyl and anisoyl derivatives of adenosine, uridine, 1-methylriboside and 1-D-ribofuranosylbenzimidazole are registrated. The possibility of identification of 2′-, 3′-O-acylribonucleosides and observation of acyl groups isomerisation kinetics is shown. The kinetics of 2′?3′ migration of a number of 2′(3′)-O-derivatives, the dependence of kinetic constants on the pH are studied. The features of acyl derivated ribonucleosides CD spectra are discussed.     

The high pressure nitric oxide mass spectra of aldehydes

The high pressure (0.5 Torr) nitric oxide mass spectra of some aldehydes, obtained using a 10% mixture of NO in N₂, are reported. The 10% NO/N₂ spectra of the monodeuterated analogs of some of them are compared to the electron-impact and methane chemical ionization spectra, especially with reference to the process of hydride abstraction by nitrosonium ions.     

The structure and dynamic behaviour in solution of the trihydridodienerhenium complexes (Ph3P)2(η-1,3-diene)ReH3

The structure and fluxionality of the trihydridodiene complexes (Ph₃P)₂(η-1,3-<di-ene)ReH₃ have been studied by NMR spectroscopy (η-1-3-diene = buta-1,3-diene, 2-methylbuta-1,3-diene, 2,3-dimethylbuta-1,3-diene, cyclohexa-1,3-diene, penta-1,3-diene, hexa-1,3-diene and hexa-2,4-diene). Several rearrangement processes have been observed; they are, in order of increasing temperature: (a) ligand interchange; (b) reversible migration of a hydride ligand on to the diene ligand, leading to η-allyl species and, in the case of the cyclohexadiene trihydride, degenerate isomerisation of the cyclohexadiene moiety; and (c), in the case of the pentadiene and hexadiene derivatives, isomerisation of the diene ligand.     

Übergangsmetall–carben-komplexe : LXXIII. Kinetik und mechanismus der isomerisierung von cis- und trans-tetracarbonyl-methoxymethylcarben-phosphin-chrom(0)-komplexen

The kinetics of the isomerisation reactions of tetracarbonyl(methoxymethylcarbene)(trialkylphosphine)chromium(0), (CO)₄Cr[C(OCH₃)CH₃] [PR₃] (R = C₂H₅, C₆H₁₁), according to the equation:

have been studied in methylcyclohexane and toluene. The interconversion of the geometrical isomers follows a first-order rate law: d[(II)]/dt = k₁[(II)]. Excess of free phosphine or carbon monoxide has no significant influence on the rate of the reaction. Phosphine exchange experiments also show that the isomerisation takes place via neither a phosphine nor a C cleavage. The results are discussed on the basis of an intramolecular isomerisation mechanism, which also plausibly explains the very small values of the activation entropies.     

Synthese und reaktivität von siliciumübergangsmetallkomplexen : X. Übergangsmetall → carbanion-übertragung von fluorsilyleinheiten,ein weg zu fluorsilyl-substituierten phosphor-yliden

The trifluorophosphine complex RhH(PF₃)(PPh₃)₃, the analogue of the well-known homogeneous catalyst RhH(CO)(PPh₃)₃, has been synthesised and found to be a highly active catalyst for both the hydrogenation and isomerisation of terminal olefins, and the complex RhH(PF₃)₂ (PPh₃)₂ has been found to bring about rapid isomerisation of terminal olefins.     

Thermal and plasma synthesis of metal oxide nanoparticles from MOFs with SERS characterization

Aluminum oxide (Al₂O₃) and chromium oxide (Cr₂O₃) nanoparticles were synthesized by thermolysis of metal-organic frameworks (MOFs). Further O₂ plasma treatment is required to obtain high crystalline quality metal oxides. The composition and morphology of metal oxide nanoparticles were confirmed by powder X-ray diffraction and scanning electron microscopy characterization, respectively. The quality of synthesized metal oxides was also examined by observing the surface-enhanced Raman scattering (SERS) spectra of methyl orange adsorbed on Al₂O₃ and Cr₂O₃. The observed SERS effect can be ascribed to charge-transfer (CT) resonance effect between methyl orange and metal oxide surfaces. UV–vis absorption spectra and DFT calculations of metal oxide- methyl orange complexes have confirmed that the observed SRS effect is due to CT resonance between the metal oxide nanoparticles and the adsorbed methyl orange molecules.     

An infrared study of the formation and photochemical decomposition of tetrachlorocyclopentadienone O-oxide in low temperature matrices

Photolysis of tetrachlorodiazocyclopentadiene at 12 K in Ar or N₂ matrices containing O₂ yields tetrachlorocyclopentadienone and tetrachloro-2-pyrone. Matrix i.r. spectra are reported for each of these products. The reaction proceeds by the addition of O₂ to the previously identified carbene, tetrachlorocyclopentadienylidene, giving initially the highly labile carbonyl oxide, tetrachlorocyclopentadienone O-oxide. The identification of the carbonyl oxide was assisted by experiments using isotopically labelled O₂, and this reactive intermediate has now been characterized in low temperature matrices by both u.v.-visible and i.r. spectroscopy.