The anionic alkylation of easily reducible arenes. A photochemical route to nucleophilic aromatic substitution of anthracene by organolithiums

High yield nucleophilic addition ensues upon mixing tetrahydrofuran solutions of benzyllithium or cyclooctadienyllithium and anthracene at low temperatures At least part of this addition proceeds by a single electron transfer pathway. Photolysis of the resulting adducts leads to the elimination of lithium hydride, giving net nucleophilic substitution in approximately 50% yield. The analogous reaction fails with naphthalene, where photolysis of the organolithium/ arene mixture leads to dimeric products derived from the organolithium.     

Lumineszenzspektren von ein- und zweikernigen Chrom(III)-Glycin-Komplexverbindungen

The luminescence spectra of the polycrystalline compounds [Cr(CH₂NH₂COO)₃ · H₂O] and [Cr₂(OH)₂(CH₂NH₂COO)₄] are investigated in the temperature range of 120K – 4.2K. From the known crystal structure (P2_1/c =D _2h ^/5 ) of the mononuclear compound assignment of the zero-phonon bands based on crystal field theory becomes possible. Both of the highly intense phosphorescence transitions are observed at \(P_1 = 14493 cm^{ - 1} ({}^2A'' \xrightarrow{{0.0}} {}^4A) and P_2 = 14428 cm^{ - 1} ({}^2A' \xrightarrow{{0.0}} {}^4A)\) . Assignment of the accompanying vibronic bands is made from the measured infrared data. Crystal field parameters Dq, B and C are determined from the luminescence and reflectance spectra. In the case of the binuclear compound the Cr³⁺-Cr³⁺ interaction via hydroxyl brides may be described by an axchange operator \(H_{ex} = - 2 \sum\limits_{ij} {J_{ij} S_i^a \cdot S_j^a } \) and from this the energy level diagram is calculated. Both observed strong phosphorescence bands at 14369 cm^?1 and 14184 cm^?1 are assigned to \(\left| {{}^2E \cdot {}^4A_2 \rangle _{s = 2} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 2} and \left| {{}^2E \cdot {}^4A_2 \rangle _{s = 1} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 1} \) transitions.     

Glycosyl alkoxythioimidates as complementary building blocks for chemical glycosylation

It is reported that S-glycosyl O-methyl phenylcarbamothioates (SNea carbamothioates) have a fully orthogonal character in comparison to S-benzoxazolyl (SBox) glycosides. This complete orthogonality was revealed by performing competitive glycosylation experiments in the presence of various promoters. The results obtained indicate that SNea carbamothioates have a very similar reactivity profile to that of glycosyl thiocyanates, yet are significantly more stable and tolerate selected protecting group manipulations. These features make the SNea carbamothioates new promising building blocks for further utilization in oligosaccharide synthesis.     

Scaling laws for gas-solid riser flow through two-fluid model simulation

Scale up of gas-solid circulating fluidized bed (CFB) risers poses many challenges to researchers.In this paper,CFD investigation of hydrodynamic scaling laws for gas-solid riser flow was attempted on the basis of two-fluid model simulations,in particular,the recently developed empirical scaling law of Qi,Zhu,and Huang (2008).A 3D computational model with periodic boundaries was used to perform numerical experiments and to study the effect of various system and operating parameters in hydrodynamic scaling o...     

A monopole mass filter with a hyperbolic V-shaped electrode

In this article we compare the classical monopole mass filter of von Zahn and the monopole mass filter with a hyperbolic V-shaped electrode. The experimental results and those of computer simulation for both mass spectrometers are presented. We show that the replacement of a conventional 90 degrees V-shaped electrode by an electrode with a hyperbolic profile substantially improves the peak shape of any given mass, and increases the mass resolution by a factor of 3-4 and the abundance sensitivity by a factor of 100. The potential of high analytical performance combined with electroforming techniques for electrode manufacture indicate future practical uses of such instruments. Copyright 1999 John Wiley & Sons, Ltd.     

A three body approach to study the structural properties of 2-n halo nuclei and the search for Efimov states

The discovery of neutron rich isotopes of the lightest elements on the neutron drip line exhibiting a halo structure has opened up new vistas in research activities. The novel structural features associated with the halo phenomena have been the subject for extensive theoretical and experimental investigations in recent times. In this talk, I propose to present a broad overview of the recent developments in this field, bringing out the striking features which show that a large number oflight nuclei near the neutron drip line are characterized by a clear separation between a ‘normal’ core nucleus and a loosely bound low density veil of neutrons. Specifically, the two neutron halos offer a natural premises, from a theoretical standpoint, to employ three body techniques for studying their detailed structural properties. A considerable part of the talk will be devoted to report and highlight the results on a number of light halo nuclei such as ¹¹Li, ¹¹Be, ¹⁹B and ²²C on which we have been carrying out investigations employing a simple but realistic three body model. These three body systems which have been termed as ‘Borromean’ (i.e while three body systems are bound, the corresponding binary subsystems on the other hand are unbound) are characterized by large spacial extension and very low separation energy of the neutron. They are, therefore, ideally suited for exploring the possibility of the existence of Efimov states in two neutron halo nuclei. We have recently carried out the three body analyses to predict the possibility of the occurrence of such states on which experimental work at various laboratories is underway.     

Novel Synthesis of Linear Furonaphthoquinones

An efficient synthesis of naturally occurring and biologically active furonaphthoquinones is described starting from suitably substituted dihydronaphthofuraps.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.