Stereochemistry of the Conversion of 2‐Phenoxyethanol into Phenol and Acetaldehyde by Acetobacterium sp.

The conversion of 2‐phenoxyethanol to phenol and acetate by the anaerobic bacterium Acetobacterium sp. strain LuPhet1 proceeds through acetaldehyde with concomitant migration of a H‐atom from C(1) to C(2) of the glycolic moiety. Separate feeding experiments with (R)‐ and (S)‐2‐phenoxy(1‐²H)ethanol, prepared via chemoenzymatic syntheses, indicate that the H‐atom involved in the 1,2‐shift is the pro‐S one of the enantiotopic couple of the alcohol function.     

Effect of a proximal substituent on the triruthenium dodecacarbonyl-catalyzed reductive carbonylation of nitroarenes

Three nitroarenes were submitted to Ru₃(CO)₁₂-catalyzed reductive carbonylation in acetonitrile and in cis-cyclooctene. The main reaction products were the corresponding amines, ureas and six- or five-membered cyclization products. Optimization of the reaction varying the temperature, the CO pressure, the catalyst/substrate ratio and the reaction time and a statistical analysis of conversion and selectivity data allow to suggest a reaction mechanism in some reaction conditions.     

Unrestricted hartree fock wave functions and hyperfine coupling constants in aromatic radicals

It is shown that a simple expression, differing from the one currently used, must be adopted when calculating electron spin densities from unrestricted H.F. wave functions in connection with the prediction of proton hyperfine couplings in aromatic free radicals. The proposed formula gives results which are almost identical to those one obtains after complete projection of the unwanted parts of the unrestricted function.

---

Zusammenfassung Es wird gezeigt, daß sich bei der Berechnung von -Elektronen-Spindichten mit Hilfe uneingeschränkter Hartree-Fock-Funktionen im Zusammenhang mit der Vorhersage von Protonen-Hyperfeinkopplungskonstanten in aromatischen Radikalen ein einfacher, von dem häufig verwandten abweichender Ausdruck ergibt. Die vorgeschlagene Formel führt zu Ergebnissen, die fast mit denen identisch sind, die man nach vollständiger Projektion der unerwünschten Anteile der uneingeschränkten Funktion erhält.

---

Résumé Une expression simple, différant de celle couramment admise, est adopté pour le calcul des densités de spin -électronique par les fonctions H.F. non-restreintes, afin de prédire les couplages hyperfins protoniques dans les radicaux benzéniques. Les résultats sont presqu'identiques à ceux de l'élimination, par projection, des parties à spin faux de la fonction nonrestreinte.

     

A computer simulation study of the ordered phases of some mesogenic fullerene derivatives

We present a Monte Carlo simulation study of the phase behaviour and molecular organization of a system of fullerene-based mesogens, represented by a three-site model composed of a fullerene sphere and two mesogenic moieties rigidly attached to it. It is shown that a combination of suitably modified Lennard-Jones and Gay–Berne attractive–repulsive potentials allows a satisfactory qualitative modeling of the interactions between the fullerene derivatives under investigation. Indeed, simulation results show that, despite the crude representation of the molecular structure, our model generates nematic and smectic phases, thus accounting qualitatively for the basic experimental observations on the class of compounds considered.     

The different photoisomerization efficiency of azobenzene in the lowest n pi* and pi pi* singlets: the role of a phantom state

Azobenzene E<==>Z photoisomerization, following excitation to the bright S(pi pi*) state, is investigated by means of ab initio CASSCF optimizations and perturbative CASPT2 corrections. Specifically, by elucidating the S(pi pi*) deactivation paths, we explain the mechanism responsible for azobenzene photoisomerization, the lower isomerization quantum yields observed for the S(pi pi*) excitation than for the S1(n pi*) excitation in the isolated molecule, and the recovery of the Kasha rule observed in sterically hindered azobenzenes. We find that a doubly excited state is a photoreaction intermediate that plays a very important role in the decay of the bright S(pi pi*). We show that this doubly excited state, which is immediately populated by molecules excited to S(pi pi*), drives the photoisomerization along the torsion path and also induces a fast internal conversion to the S1(n pi*) at a variety of geometries, thus shaping (all the most important features of) the S(pi pi*) decay pathway and photoreactivity. We reach this conclusion by determining the critical structures, the minimum energy paths originating on the bright S(pi pi*) state and on other relevant excited states including S1(n pi*), and by characterizing the conical intersection seams that are important in deciding the photochemical outcome. The model is consistent with the most recent time-resolved spectroscopic and photochemical data.     

Storage ring free electron laser dynamics in presence of an auxiliary harmonic radio frequency cavity

In a Storage Ring Free Electron Laser (SRFEL) there is a strong interdependence between the laser beam and the electron beam from which the laser is generated. The Super ACO storage ring has a second Radio Frequency (RF) cavity at the 5th harmonic of the main RF cavity. It is used to shorten the bunch length, thereby enhancing the laser gain. Employing this RF harmonic cavity instabilities are observed with a strong effect on both the laser radiation properties and the electron beam behaviour. In this paper, we first present beam characteristics of Super-ACO as influenced by the harmonic cavity, and the instabilities of the beam due to this RF cavity. Then we discuss the FEL properties in presence of the harmonic RF cavity. In general the harmonic cavity functions as intended, and it is observed that the laser suppresses the instabilities caused by the harmonic cavity in the absence of the FEL.     

A Simple Proof of Stability of Fronts¶for the Cahn–Hilliard Equation

We apply a method developed in our earlier work on a non-local phase kinetics equation to give a simple proof of the non-linear stability of fronts for the Cahn–Hilliard equation. Received: 14 November 2000 / Accepted: 30 July 2001     

Closure and Convexity Results for Closed Relativistic Strings

We study various properties of closed relativistic strings. In particular, we characterize their closure under uniform convergence, extending a previous result by Y. Brenier on graph-like unbounded strings, and we discuss some related examples. Then we study the collapsing profile of uniformly convex planar strings which start with zero initial velocity, and we obtain a result analogous to the well-known theorem of Gage and Hamilton for the curvature flow of plane curves. We conclude the paper with the discussion of an example of weak Lipschitz evolution starting from the square in the plane.