Reactions of (1‐nitroethenyl)sulfonylbenzene,a nitroethene derivative geminally substituted by a second W‐group

Nitroaldol reaction of phenylsulfonylnitromethane with formaldehyde affords a mixture of 2,4‐dinitro‐2,4‐bis(phenylsulfonyl)butan‐1‐ol and 2,4‐dinitro‐2,4‐ bis(phenylsulfonyl)pentane‐1,5‐diol. Treatment of this mixture with base followed by reacidification affords 1,1'‐[(1,3‐dinitro‐1,3‐propanediyl)bis(sulfonyl)]bis(benzene) as a mixture of (R*, R*) and (R*, S*)‐diastereomers from which the (R*, S*)‐diastereomer can be obtained pure. The intermediate in the nitroaldol reaction is (1‐nitroethenyl)sulfonylbenzene and, if dienes are present, additional products are also obtained. If either (E)‐2‐methyl‐1,3‐pentadiene or 1‐(1‐methylethenyl)cyclohexene are present, typical Diels‐Alder adducts are obtained with the major isomers explainable by assuming a transition state in which the nitro group is endo. If furan is present, its formal conjugate addition product, 2‐[2‐nitro‐2‐(phenylsulfonyl)ethyl]furan, is formed. If cyclooctatetraene is present, it first dimerizes and then affords isomeric Diels‐Alder cycloadducts of the dimer. Semiempirical calculations comparing the LUMO energies of (1‐nitroethenyl)sulfonylbenzene to the corresponding trans‐1,2 isomer are presented to explain relative reactivity of 1,1‐ and 1,2‐disubstituted dienophiles. Copyright © 2009 John Wiley & Sons, Ltd.     

Selectivity of nitro versus fluoro substitution in arenes in their reactions with charged O‐ and S‐nucleophiles

The relative mobility of nitro and fluoro substituents in 1,3‐dinitro‐ and 1‐fluoro‐3‐nitrobenzenes, 3,5‐dinitro‐ and 3‐fluoro‐5‐nitrobenzotrifluorides under the action of the nucleophiles (2ArYH)·K₂CO₃ and ArY^?K⁺ in solution and the nucleophiles ArYH·K₂CO₃ (Y = O, S) under heterogeneous conditions was studied by a competitive method in DMF at 40–140 °C. The unique dependences of ΔΔH^≠ on ΔΔS^≠ and ΔΔH^≠ on ΔΔG^≠ were determined for all the substrates and nucleophiles. The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions studied: (i) substituent effects in the nucleophiles (2ArYH)·K₂CO₃ and ArYH·K₂CO₃ on the activation entropies suggest that the entropy favours the displacement of nitro group; (ii) the negative signs of ΔΔH^≠ and ΔΔS^≠ for the reactions of the nucleophiles ArY^?K⁺ indicate that the enthalpy determines the displacement of nitro group. It is concluded that the selectivity of the reactions with aryloxide and arylthioxide ions cannot be explained by the hard–soft acid–base principle only. Copyright © 2007 John Wiley & Sons, Ltd.     

Electron Spin Resonance Study of the Solvent Effect on the Conformation of Some Iminoxy Radicals

The reaction of nitrogen dioxide with carbonyl compounds having a methylene or vinyl group adjacent to the corbonyl leads to the formation of stable iminoxy radicals^1-3. Evidence^1,2,4 has been presented that the precursor of these iminoxy radicals is probably the corresponding oxime formed by rearrangements of the intermediate nitroso compounds. There have also been reports on the e.s.r. detection of some cis-trans isomers of some iminoxy radicals in methanol or in neat liquid^1,5. We wish to report here a drastic solvent effect on the conformations of some iminoxy radicals formed by the reaction of NO₂ with trifluoroacetylacetone.     

Interpretation of NO2 absorption in twilight sky spectra

A multiple scattering model has been developed to calculate nitrogen dioxide (NO₂) absorption in the light from the zenith sky during twilight. Model studies show that this absorption is not very sensitive to the atmospheric temperature profile or to tropospheric NO₂.The model was used to interpret some ground-based measurements of NO₂ sky absorption. Values for the total stratospheric column amount vary from 2 to 12×10¹⁵moleccm^-2, and the mean altitude of the stratospheric concentration profile is around 35 km. These observations are in broad agreement with those of other workers.     

Vanadium phosphates on mesoporous supports: model catalysts for solid-state NMR studies of the selective oxidation of n-butane

SBA-15 was utilized as mesoporous support for the dispersion of vanadium phosphate (VPO) compounds. Loading of SBA-15 with VPO compounds was found to be accompanied by decreasing ²⁹Si MAS NMR signals of Q² (Si(2Si,2OH)) and Q³ (Si(3Si,1OH)) silicon species, which indicates coverage of the mesoporous support by the guest compounds. The ⁵¹V MAS NNR spectra of the activated VPO/SBA-15 catalysts consist of patterns typical for the α_II- and β-phases of vanadyl orthophosphate. In the ³¹P MAS NMR spectra of the activated VPO/SBA-15 catalysts, signals of β-, δ-, and α_II-VOPO₄ phases could be identified. Upon conversion of n-butane-¹³C₄, a strong decrease of the ³¹P MAS NMR signals characteristic for the δ-VOPO₄ phase occurred, while by ¹³C MAS NMR spectroscopy the formation of maleic anhydride, carbon monoxide, and carbon dioxide was observed. This finding supports the active role of the δ-VOPO₄ phase in the selective oxidation of n-butane on VPO/SBA-15 catalysts.     

Difference between 1H NMR signals of primary amide protons as a simple spectral index of the amide intramolecular hydrogen bond strength

The effect of the intramolecular H‐bonding of the primary amide group on the spectral properties and reactivity of this group towards electrophiles has been studied in systematic rows of 1,2,5,6,7,8‐hexahydro‐7,7‐dimethyl‐2,5‐dioxo‐1‐R‐quinoline‐3‐carboxamides and 2‐aryliminocoumarin‐3‐carboxamides using ¹H and ¹⁵N NMR spectroscopy and the kinetics of model reactions. The upfield signal of the amide proton that is not intramolecularly H‐bonded (H^a) depends on external factors such as solvent nature and concentration. At the same time, the downfield chemical shift of the H^b proton (bonded by the intramolecular hydrogen bond) depends mostly on the strength of the intramolecular H‐bond, which is affected by such internal factor as electron nature of substituent R. The substituent's influence on the H^b proton's chemical shift is more effective in deuterochloroform medium than in DMSO‐d₆ where the intramolecular hydrogen bond is less stable. The value Δδ(H) = δ(H^b) ? δ(H^a) is suggested as a simple comparative spectral index of the intramolecular hydrogen bond strength in these and similar compounds. By contrast, the effect of R on the ¹⁵N NMR chemical shift of the amide nitrogen has turned out to be too small to estimate changes of the electron density at the nitrogen. The effect of the intramolecular H‐bond on the reactivity of the amide group is twofold. When the cleavage of the H‐bond occurs on the rate limiting step it dramatically reduces the reaction rate. In the other case, the strengthening of the H‐bond favors the reaction rate because of the increase of the electron density at the amide nitrogen. Copyright © 2011 John Wiley & Sons, Ltd.     

Microwave-optical double resonance in NO2

A series of experiments performed to establish the nature of the previously reported microwave optical double resonance signals in electronically excited nitrogen dioxide are reported. The DC stark effect, hyperfine spectrum, and microwave saturation behavior of the double resonance signals observed by exciting NO₂ with the 4880 Å line of an argon ion laser have been studied. The data presented support the assignment of this double resonance signal as occurring within the rovibronic manifold of the ²B₂ electronic state. The observation of a number of new excited state microwave transitions is also reported.     

Removal of carbon dioxide from gas mixtures by wollastonite

Wollastonite synthesis and decomposition were analyzed from the viewpoint of thermodynamics (using the TERRA software). It is shown that wollastonite synthesis from limestone and silica takes place at a minimum content of nitrogen (10^?5 N₂) with a release of carbon dioxide. The synthesis temperature is T ≥ 560 K. Wollastonite is decomposed in the presence of flue gas (4N₂) with limestone and silica formation and burial of carbon dioxide in the form of CaCO₃(c). Wollastonite decomposition temperature is T ≤ 420 K. The cyclic reciprocating process for complete removal of carbon dioxide by wollastonite is suggested. Four strokes of the reciprocating system with the fixed temperatures of wollastonite decomposition (T=300 K) and wollastonite synthesis (T=560 K) are presented. Total energy consumption (T = 560 K) is ΔI ≈ 130 kJ/mole, 30 % of energy is spent for heating and 70 % of energy is spent for chemical reaction. This is comparable with the heat of CO₂ solution in ethanolamin.     

Application of 15N NMR Spectroscopy to Studies of the Intermolecular Interaction of Biomolecules

Abstract

Nitrogen nuclei are frequently located at the interaction sites of biomolecules; for example, amide nitrogens in the peptide are the key to maintaining the peptide backbone conformation by hydrogen bonding. Histidine, tryptophan, and arginine side chains contain nitrogen atoms which are often located at the active sites of enzymes. Heterocyclic compounds like purine and pyrimidine bases are substances essential to information transfer by base pair formation of nucleic acids. Also some other co-factors and dyes, such as flavins, porphyrins and chlorophylls, are nitrogen-containing substances which regulate energy tranduction in biological systems. Lecithin and phosphatidylethanolamine are the principal components of the phospholipids from biomembranes. To detect interaction sites and to study the interaction mechanism of these biomolecules, the use of nitrogen NMR seems promising. Although more than 99% of naturally occurring nitrogen element has the ¹⁴N nuclei, a disadvantage of the use of ¹⁴N magnetic resonance has been recognized. It has a spin quantum number I = 1 and the associated quadrupole moment provides a very broad resonance signal of about 100～1000 Hz. Thus, for detection of small changes of the chemical environment, use of ¹⁴N magnetic resonance is not adequate. The natural abundance of ¹⁵N nuclei with a spin quantum number I = 1/2 (which give a sharp resonance signal) is only 0.3% (Table 1). But recent developments in the instrumentation of NMR spectroscopy have made it possible to observe the resonance of the nuclei with low natural abundance. Fourier transform (FT) NMR can save thousands of times the accumulation time to improve the signal to noise ratio of ¹⁵N spectra [1-3]. Also superconducting magnets with wide bores have made possible the use of thick sample tubes of 25 mmΦ and observation of the ¹⁵N resonance of substances of low solubility [4]. In spite of such instrumental development, the observation of the 15N resonance is still not easy because of its low sensitivity; about of proton magnetic resonance. In the application of ¹⁵N NMR in biological systems, we often encounter quite low solubility of biomacromolecules and also sometimes need to measure the concentration dependency of ¹⁴N chemical shifts. For such experiments, enrichment of ¹⁵N nuclei in the molecules is required. Chemical syntheses starting from the simple ¹⁵N containing compounds as an ¹⁵N source and also biological syntheses by bacterial fermentation using the ¹⁵N source in culture media are employed for ¹⁵N enrichment. Enrichment at specific positions of biomolecules is useful for spectral assignments and also for analyses of the pathways of biosyntheses [5].     

Observation of alignment of the ground state of NO<Subscript>2</Subscript> under laser excitation

A Hanle signal is observed in the absorption of a cell filled with nitrogen dioxide NO₂ at room temperature. The excitation was performed by an Ar⁺ laser at a wavelength of 476.4 nm.     

Use of GC-QMS for stable isotope analysis of environmentally relevant main and trace gases in the air

Abstract

When tracing the fluxes of N compounds (especially N oxides) and carbon dioxide in the system soil-atmosphere and applying ¹⁵N and ¹³C, it is necessary to simultaneously determine both the concentration of the substances and their isotopic composition. GC separation (packed column) was coupled to a mass spectrometer by a special interface. Variable sample volumes can be delivered by changing the split by means of the interface in front of the MS. Thus, both the concentration of a gaseous compound and its ¹⁵N content can be measured. Supplying sample volumes in a range between 5 μl and 5 ml, it is possible to measure both components of high content (e.g., nitrogen) and at the lower ppm(v)-content (e.g., dinitrogen oxide) in the air. Measurements of N₂, N₂O, NO and CO₂ are demonstrated, too.     

Mechanism of catalytic reduction of NO by H2 or CO on a Pd foil; Role of chemisorbed nitrogen on Pd

The adsorption of NO and its reaction with H₂ over polycrystalline Pd were investigated using flash desorption technique and ultraviolet photoelectron spectroscopy under 10^?5 Pa pressure range of reactants and surface temperatures between 300 and 900 K. NO was adsorbed dissociatively onto the Pd surface above 500 K, and the heat of dissociative adsorption was ca. 126 kJ/mol. Atomic nitrogen was observed to accumulate on the Pd surface during the NO-H₂ reaction, whose desorption rate exhibited second order kinetics and is expressed as follows: V_d = 10^{?9.8 ± 0.3}exp(?67(kJ/mol)/RT) (cm²/atom·s). Hydrogenation of the adsorbed nitrogen proceeded rapidly at 485 K. It was confirmed from these results that formation of N₂ and NH₃ in the NO-H₂ reaction proceeds through this atomically adsorbed nitrogen. Pd-N bond energy and enthalpies of some intermediate states of the NO-H₂ reaction were estimated.     

Theoretical studies on nitrogen‐rich furoxan‐based heterocyclic derivatives

The density functional theory method was used to study the heats of formation (HOFs), energetic properties, electronic structure of a series of 4,4″‐dinitro(3,3′:4′,3′′)tris([1,2,5]oxadiazole)‐2′‐oxide (3,4‐bis[4′‐nitrofurazan‐3′‐yl]furoxan) derivatives. The results show that the substitution of the nitro group is very useful for improving their HOFs and detonation performances. The HOFs of the title compounds are all positive and larger than those of 1,3,5‐trinitro‐1,3,5‐triazinane and 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane. The analysis of oxygen balance shows that the studied compounds need the oxygen in the explosive. Compound A1 has larger detonation velocity and detonation pressure than those of 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane and can be regarded as a potential candidate for high‐energy compounds because of the moderate heat of detonation, high density, and high N. In addition, the energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital of the studied compounds are further investigated.     

Photoinduced electron transfer in meso-nitrophenyl-substituted porphyrins and their chemical dimers

It is shown that steric interactions of volume substituents in the β-positions of pyrrole rings and the nitro group in mono-and di-meso-phenyl-substituted of octaethylporphyrins and their chemical dimers containing the electron-acceptor NO₂ group in the ortho-position of the phenyl ring at 295 K favor the direct overlap of molecular orbitals of the interacting subunits, resulting in the efficient quenching of fluorescence due to the direct electron transfer from the S₁ level to the lower-lying state via the “through-space” mechanism. The electron transfer in these compounds in nonpolar media (the rate constant k _et ^S =(3.2–9.5)×10⁹ s^?1 is nonadiabatic, whereas in strongly polar solvents (k _et ^S =2×10¹¹ s^?1) the adiabatic effects can be manifested. In compounds containing the NO₂ group in meta-or para-positions of the phenyl ring, the nonadiabatic electron transfer from the S ₁ level occurs less efficiently both in polar [k _et ^S =(0.2–5)×10¹⁰ s^?1] and nonpolar media [k _et ^S =(0.1–1.0)×10⁷ s^?1]. In this case, the electron transfer involves molecular orbitals of phenyl (the “through-bond” mechanism), and its efficiency depends on the orbital electron density in the meta-and para-positions of the phenyl ring. Based on the experimental data obtained and analysis of the electron transfer within the framework of the Marcus theory, the energy scheme of relaxation processes of the electronic energy in the compounds under study involving charge transfer states is suggested.     

Evidence for L· against LOO· being spin-trapped by 4-POBN during the reaction of Fe2+-induced lipid peroxidation

The character of a water soluble spin trap-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN) in the peroxidation of linoleic acid induced by Fe²⁺ has been studied. An ESR spectrum with six lines (a _N=1.58 mT,a _H=0.26 mT) was formed after Fe²⁺ and 4-POBN were added to linoleic acid solution. Its intensity depends on the concentration of Fe²⁺ and the incubation time of the system. It increased when the reaction solution was flushed with nitrogen, comparing with the reaction solution exposed to air at the same concentration of Fe²⁺, 4-POBN and linoleic acid. And it decreased greatly when the system was bubbled with oxygen. At the same time, the concentration of Fe²⁺ did not decrease distinctly with the existence of oxygen detected colorimetrically using phenanthroline, by ultraviolet spectruphotometer. When N-t-butyl-phenylnitrone (PBN) was used instead of 4-POBN, a similar spectrum (a _N=1.61 mT,a _H=0.32 mT) was obtained. The hyperfine coupling constants (hfcs) of the signal are very similar to that of the adduct formed from alkyl radical with PBN. According to above results it is reasonable to conclude that the trapped radical should be assigned as a carbon-centered species (i.e. L·), not the oxygen-derived peroxyl one (i.e. LOO·). The adduct of 4-POBN and L· can survive as long as two hours.     

Synthese und Qualitätskontrolle 15N-markierter Stickoxide mit hoher 15N-Häufigkeit für umweltrelevante Tracer-Untersuchungen

Für die Untersuchung ausgewählter Probleme des Verhaltens und der Wirkung der Stickoxide NO _x (NO + NO₂) in Ökosystemen, z.B. die Aufnahme und Freisetzung von NOx durch das System “Boden-Pflanze”, bietet sich der Einsatz ¹⁵N-markierter Stickoxide an. Die dazu benötigten ¹⁵N-markierten Gasgemische hoher Reinheit werden aus eigens dafür synthetisiertem [¹⁵N]Stickstoffmonoxid oder [¹⁵N]Stickstoffdioxid mit hoher ¹⁵N-Häufigkeit hergestellt. Beide Synthesen gehen jeweils von der kostengünstig kommerziell erhältlichen [¹⁵N]Salpetersäure aus.

Im Falle des [¹⁵N]Stickstoffdioxids erfolgt die Herstellung über die Präparation von Bleinitrat und dessen thermische Zersetzung. Die Ausbeute liegt bei 70–75% bezogen auf eingesetzte [¹⁵N]Salpetersäure.

Die Herstellung von [¹⁵N]Stickstoffmonoxid erfolgt durch Reduktion von [¹⁵N]Salpetersäure mit Eisen-II-sulfat in stark saurer Lösung. Die Ausbeute beträgt 60–70%, bezogen auf eingesetzte Salpetersäure.

The application of ¹⁵N is very useful for the investigation of the behavior and the effect of the nitrogen oxides NO _x (nitric oxide + nitrogen dioxide) in ecosystems, e.g. the uptake and release of NO _x by the soil-plant system. The ¹⁵N labelled gas mixture needed for that purpose has to be prepared from synthesized highly enriched [¹⁵N]nitric oxide and [¹⁵N]nitrogen dioxide. These two syntheses both use the commercially available and reasonable [¹⁵N]nitric acid.

In the case of [¹⁵N]nitrogen dioxide the synthesis is carried out via [¹⁵N]lead nitrate and its decomposition with increasing temperature. The yield is 70–75% related to the [¹⁵N]nitric acid input. The preparation of [¹⁵N]nitric oxide is done by reduction of [¹⁵N]nitric acid by means of FeSO₄ in strong acid solution. The yield amounts to 60–70%.     

Observation of magnetic Mn sites in cubic and hexagonal HoMn2: 55Mn NMR study

⁵⁵Mn nuclear magnetic resonance has been measured for both cubic C15 and hexagonal C14 HoMn₂. In the ordered state, we found a high-frequency signal, which can be assigned to magnetic Mn atoms, for both C15 and C14 phases together with a low-frequency signal from non-magnetic Mn atoms. The results of the spin-spin relaxation time T₂ in the ordered state and the NMR spectra in the paramagnetic state are also given to discuss the magnetic instability and the magnetic structure.     

The oxidation of carbon monoxide on polycrystalline rhodium under knudsen conditions: II. Reaction with nitrogen monoxide

The reaction between carbon monoxide and nitrogen monoxide on a polycrystalline rhodium ribbon under stationary conditions is followed by mass spectrometry. In the temperature range 300 to 1100 K the ratio of the partial pressures of the reactants varies between 0.1 < p_NO/p_CO < 100 at values of the total pressure in the reactor from 10^?4 to 10^?5 Torr. The results can be interpreted qualitatively by a simple elementary reaction sequence. Simulation using literature values of the kinetic constants leads to semi-quantitative agreement with experimental results. No isothermal oscillations of the reaction rate could be observed under the stated conditions.     

Reversible Photoisomerization of β-Methyl-β-Nitrostyrene: The Role of Triethylamine

The photolysis of trans-β-nitro-βmethylstyrene in acetonitrile solution gives the cisisomer with a quantum yield of 0.8. Addition of triethylamine to the system leads to a small decrease in the photoisomerization quantum yield and the appearance of a strong EPR signal. This signal remains for several hours at the end of the irradiation. It is demonstrated that the EPR signal is associated to an intermediary produced during the triethylamine catalyzed thermal back formation of the trans isomer. This intermediary bears an unpaired electron mostly associated to the nitro group and suggest that the thermal back reaction takes place by an initial electron transfer from the amine to the nitro group, leading to a long lived zwitterionic biradical.     

Fluorescence from the 2B1 state of NO2 excited at 4545 Å

The 4545 Å line of the Ar⁺ laser has been used to excite a ^pR₁ line of a vibrational band of the ²B₁-²A₁ system of nitrogen dioxide. Fluorescence from the upper level to the ground electronic state forms a long progression in the bending vibration. This progression can be followed from v″₂ = 0 up to v″₂ = 12, and the fluorescence intensity passes through several local minima as a function of v″₂. The main features of the intensity distribution can be reproduced using a model Hamiltonian which separates the bending and rotation from the stretching vibrations. This Hamiltonian can also be used to reproduce the fluorescence frequencies by adjusting the potential function of the lower state.