Efficient copper-mediated reactions of nitrenes derived from sulfonimidamides

[reaction: see text] Sulfonimidamides lead efficiently to nitrenes and have been converted to sulfimides, sulfoximines, and aziridines in good yields, through a copper-mediated multicomponent reaction. The stereogenic sulfur atom and the trivalent nitrogen atom present in the molecules open the way to asymmetric synthesis, whose first results are presented.     

A study of coronene—coronene association using atom—atom pair potentials

A study of the coronene—coronene association using different interaction potentials based on an atom-atom pair potential proposed by Fraga has been performed. The interaction potentials employed differ in the way the electrostatic and/or dispersion contributions are computed. The influence of both contributions on the geometries predicted for the coronene dimer is discussed in order to analyze the effectiveness of the different interaction potentials. The stationary points found in each interaction energy hypersurface are characterized by calculating the Hessian eigenvalues. Results are discussed in the light of those previously reported for the benzene dimer. Stacked-displaced structures are suggested to be the preferred conformations for the coronene—coronene association. © 1996 John Wiley & Sons, Inc.     

Mndo investigation of the 1,2-rearrangement of singlet carbenes and nitrenes

1,2-Rearrangement of substituted methylcarbenes, carbonylcarbenes, methyinitrenes and carbonyltrenes have been calculated for singlet states by MNDO. The alteration in the electronic structure along the reaction course has been investigated by calculation and analysis of the transformation matrices between the MO's of the educts and the transition states. Migratory aptitudes are discussed as well as factors by which they may be determined. The effect of substituents at different positions has been investigated and conformational influences are discussed. As far as experimental results exist, the calculated data agree very well and offer a detailed understanding for the reaction mechanism and substituent effects.     

Ion cyclotron resonance mass spectrometric study of ion—molecule reactions in toluene—pyridine mixtures

Ion—molecule reactions in toluene, toluene-d₈, pyridine, 4-methyl-, 4-ethyl- and 4-terr-butylpyridine and quinoline and their mixtures were studied by ICR mass spectrometry at 10^-7 Torr (1 Torr = 133.3 Pa). The reactions of benzyl (m/z 91), benzyl-d₇ (m/z 98), methylbenzyl (m/z 105), and azabenzyl (m/z 92) ions with pyridines and quinoline were observed. The reactions of protonated pyridines with unprotonated molecules leading to homoconjugated ions (BHB)⁺ were detected.     

Classical path sudden approximations for atom—rigid rotor collisions

The classical path sudden approximation has been used to calculate cross sections for rotational excitation in atom—molecule collisions. Three different decoupling approximations for the angular momentum of the molecule are used: one effective potential approach and two different coupled states approaches, all in their semiclassical versions. Numerical results are presented and discussed for the systems Ar---N₂, Ar---Li₂, Ar---LiH, He---CO and Ar---HCl assumming intermolecular potentials of P₁ symmetry, P₂ symmetry and combinations.     

Solution phase isomerization of vibrationally excited singlet nitrenes to vibrationally excited 1,2-didehydroazepine

Photolysis of phenyl and o-biphenylyl azide (at 270 nm) releases vibrationally excited singlet nitrene which isomerizes to the corresponding hot 1,2-didehydroazepine at a rate competitive with thermal relaxation. Using ultrafast vibrational spectroscopy we observe the formation of vibrationally excited 1,2-4,6-azacycloheptatetraene (1,2-didehydroazepine) in picoseconds following photolysis of phenyl azide in chloroform and o-biphenylyl azide in acetonitrile at ambient temperature.     

Synthesis of nitrogen-doped carbon nanostructures by the reactions of small molecule carbon halides with sodium azide

Nitrogen-doped carbon nanostructures including particles, whiskers, square frameworks, lamellar layers, hollow spheres, and tubular structures have been successfully synthesized by designed direct chemical reactions of small molecule carbon halides (such as CCl4, C2Cl6) and nitridation reagent NaN3 in the absence of any templates and catalysts. The N/C ratios of the as-prepared CNx nanostructures (0.01 approximately 0.33) are strongly and systematically related to the reaction temperatures and the choice of carbon sources, as well as the presence or absence of the solvent. The Raman spectra indicate that the approaching graphitization process has occurred as the reaction temperature increases. The possible reaction mechanisms for the formation of the hollow structures are tentatively discussed according to the experimental results. This strategy provides an alternative route to synthesize nitrogen-doped carbon nanostructures and is expected to open up a new route for the synthesis of carbon nitrides.     

Kinetics of atom–photon Interactions

In order to avoid the violation of basic principles of macroscopic reversibility and detailed balance, we propose a cell kinetic model for atom-photon interactions instead of Enstein's classical photon kinetic mechanism. Our model can be interpreted as a generalization of either mass action law or Einstein's original scheme. © 1995 John Wiley & Sons, Inc.     

Anisotropy of atom–atom repulsions

We describe investigations of the short-range repulsion part of the intermolecular potential using a test particle approach. This approach provides an economical method of constructing reasonably accurate model repulsion potentials and demonstrates the importance of anisotropy in describing the short-range repulsion. © 1994 by John Wiley & Sons, Inc.     

MCSCF study of singlet oxygen addition to ethenol—a model of photooxidation reactions of unsaturated and aromatic compounds bearing hydroxy groups

The reaction path of singlet (¹Δ_g) oxygen addition to ethenol (vinyl alcohol)—a model of the reactions of singlet oxygen with aromatic and unsaturated compounds bearing the hydroxy groups—has been studied by means of MCSCF calculations, using various active spaces and basis sets. The effects of dynamic correlation (at the PT2 level) and basis set superposition error (BSSE) on relative energies were also investigated. It was found that including polarization functions is necessary to obtain geometries of the oxygen moiety consistent with the available experimental data. Two possible reaction products were considered: 1-hydroxy-1,2-dioxethane (peroxide) and 2-hydroperoxyethanal-1 (hydroperoxide); their energies are 24.1 and 36.6 kcal/mol (44.1 and 78.2 kcal/mol with the PT2 contribution and BSSE correction) below the dissociation limit, respectively (all energies reported here refer to the 6-31G** basis set and an active space composed of eight orbitals and ten electrons). A common stage of both reactions is the formation of a peralcoxyl intermediate with one of the oxygen atoms attached to the unsubstituted carbon atom; the energies of the respective transition state and that of the intermediate are 30.2 and 18.7 kcal/mol (15.9 and 10.3 kcal/mol with the PT2 contribution and BSSE correction) above the dissociation limit, respectively. The energy of this transition state is the dominant energy barrier to the reaction. The intermediate can then undergo conversion to the dioxethane product, to the perepoxide intermediate, or via a proton transfer, directly to the hydroperoxide, the last route being the most probable one. The perepoxide intermediate, after a proton transfer, also readily gives the hydroperoxide. It was also found that the unimolecular conversion from dioxethane to hydroperoxide via a proton transfer from the hydroxy group accompanied with ring cleavage requires an activation energy of at least 56 kcal/mol, making this reaction path highly improbable. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1668–1681, 1997     

Ion–molecule reactions of fragment ions derived from protonated allyl methyl ether

Unusual behaviour has been noted for allyl methyl ether (1) chemically ionized in a high-pressure ion source. Tandem mass spectrometry indicates the formation of methylcyclopentadienyl and methoxy-1-propenylcarbenium ions (d, m/z 81 and e, m/z 85). The origin of these unexpected ions has been elucidated using conventional and Fourier transform ion cyclotron resonance experiments: primary fragment ions derived from protonated 1 (allyl ions a and methoxymethyl cations b) generate collision complexes with neutral 1, giving rise to the ions d and e, respectively, after methanol elimination.     

Spin‐coupled study of addition reactions of singlet dihalocarbenes with ethene

Modern valence bond theory, in its spin‐coupled form, is used to examine the electronic rearrangements that take place during the gas‐phase additions of singlet CF₂ and of singlet CCl₂ to ethene. Both reactions are found to follow homolytic pathways, during which the ethene π‐bond breaks and the orbitals that were originally involved in this bond interact with the singlet orbital pair on the carbene. The formation of the two new σ bonds that close the cyclopropane ring proceeds in a markedly asynchronous manner, so that the systems attain considerable diradical character, as quantified by the composition of the active‐space spin‐coupling pattern. The rearrangement of the electron spins from a reactant‐like form to one better suited to the product takes place much later in the case of the reaction between CCl₂ and ethene than in the corresponding reaction of CF₂. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Yields of O2(b1Σ) from reactions of HO2

A discharge-flow apparatus with resonance fluorescence and chemiluminescence detection has been used to monitor O₂(b ¹σ) production from several reactions of the HO₂ radical at 300 K and 1-torr total pressure. O₂(b), HO₂, and OH were observed when F atoms were added to H₂O₂ in the gas phase. Signal strengths of O₂(b) were proportional to initial concentrations of H₂O₂ and HO₂. These observations were analyzed by using a simple three step mechanism and a more complete computer simulation with 22 reaction steps. The results indicate that the F + HO₂ reaction yields O₂(b) with an efficiency of (3.6 ± 1.4) × 10^?3. By monitoring [O₂(b)] and [HO₂] upon addition of an excess second reactant to HO₂, O₂(b) yields from the reactions of HO₂ with O, Cl, D, H, and OH were found to be <1 × 10^?2, <5 × 10^?4, <2 × 10^?3, <8 × 10^?3, and <1 × 10^?3, respectively. Yields of O₂(b) from the HO₂ ± HO₂ reaction were found to be less than 3 × 10^?2.     

N-tosyloxycarbamates as a source of metal nitrenes: rhodium-catalyzed C-H insertion and aziridination reactions

The rhodium-catalyzed decomposition of N-tosyloxycarbamates to generate metal nitrenes which undergo intramolecular C-H insertion or aziridination reaction is described. Aliphatic N-tosyloxycarbamates produce oxazolidinones with high yields and stereospecificity through insertion in benzylic, tertiary, and secondary C-H bonds. Intramolecular aziridination occurs with allylic N-tosyloxycarbamates to produce aziridines as single diastereomers. The reaction proceeds at room temperature using a rhodium catalyst and an excess of potassium carbonate and does not require the use of strong oxidant, such as hypervalent iodine reagents. A rhodium nitrene species is presumably involved, as both reactions are stereospecific.     

Periodane—An unexpectedly stable molecule of unique composition

Structure, bonding characteristics, and reaction energies as well as optical, vibrational, and nuclear magnetic resonance (NMR) properties of the hitherto unknown molecule LiBeBCNOF, called periodane, have been calculated by quantum chemical methods. It can be shown that periodane is stable enough to be produced and identified experimentally. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006