Ab initio n-electron valence state perturbation theory study of the adiabatic transitions in carbonyl molecules: formaldehyde, acetaldehyde, and acetone

The application of the recently developed second-order n-electron valence state perturbation theory (NEVPT2) to small carbonyl molecules (formaldehyde, acetaldehyde, and acetone) is presented. The adiabatic transition energies are computed for the singlet and triplet n-->pi(*), pi-->pi(*), and sigma-->pi(*) states performing a full geometry optimization of the relevant states at the single state CASSCF level and taking into account the zero point energy correction in the harmonic approximation. The agreement with the known experimental values and with previously published high level calculations confirms that NEVPT2 is an efficient tool to be used for the interpretation of molecular electronic spectra. Moreover, different insight into the nature of the excited states has been obtained. Some of the transitions presented here have never been theoretically computed previously [(3)(pi-->pi(*)) and (3)(sigma-->pi(*)) adiabatic transitions in acetaldehyde and acetone] or have been studied only using moderate level (single reference based) ab initio methods (all adiabatic transitions in acetaldehyde). In the present work a consistent disagreement between NEVPT2 and experiment has been found for the (3)(pi-->pi(*)) adiabatic transition in all molecules: this result is attributed to the low intensity of the transition to the first vibrational levels of the excited state. The n-->pi(*) singlet and triplet vertical transition energies are also reported for all the molecules.     

Metalation of 2-chloromethyl-2-oxazolines: synthesis of 1,2,3-tris(oxazolinyl)cyclopropanes and derivatives

2-Chloromethyl-2-oxazoline converts cleanly into trans-1,2,3-tris(oxazolinyl)cyclopropane upon treatment with strong bases such as LDA or KN(SiMe(3))(2). Deprotonation of the above cyclopropane followed by the addition of electrophiles allows the preparation of more functionalized tris(oxazolinyl)cyclopropanes.     

Michael addition of chloroalkyloxazolines to electron-poor alkenes: synthesis of heterosubstituted cyclopropanes

Lithiated 2-(1-chloroethyl)-4,4-dimethyl-2-oxazoline 7 adds to electron-poor alkenyl heterocycles to afford substituted cyclopropanes in excellent yields. A route to chiral nonracemic heterosubstituted cyclopropanes, starting from optically active 2-chloromethyl-2-oxazolines, is highlighted as well.     

Optimization of membrane area and catalyst distribution in a permeative-stage membrane reactor for methane steam reforming

Methane steam reforming to produce high purity hydrogen is conveniently carried out in membrane reactors. The interest on this process has led to several studies about the influence of the key operating variables on the system performances. In the present paper we focus on the optimization of the catalyst and membrane area axial distribution by computer simulation. To this purpose, a numerical model of a permeative-stage membrane reactor (PSMR), a system composed of traditional reactive and membrane permeative stages laid out in alternated series, has been developed. This is based on 1D mass, momentum and energy balances including thermal effects on all the system properties. First, an equi-sized nine-stage PSMR is analyzed at various temperatures and membrane thicknesses, in comparison with a conventional membrane reactor, showing that improved performances, especially in terms of methane conversion, can be obtained. Then, considering the stage lengths as design variables, the optimal system performances are determined by maximizing two objective functions, namely the methane conversion and the hydrogen recovery factor. Different optimal length distributions are found utilizing the two criteria, corresponding to privileged kinetic or permeative aspects. In comparison to the conventional MR, the PSMR leads to a higher conversion and lower recovery factor when the conversion is maximized, whilst the opposite situation occurs when maximizing the recovery factor. Furthermore, the role of the heat exchange area between the furnace and the reactor is studied, considering a PSMR with adiabatic permeative stages. From this case, it is possible to see that the greater advantage of this apparatus (having the same membrane area, catalyst amount and heat-exchange area as the MR) consists in a much higher recovery factor (+21% ca.), which at the end demonstrates to be the most convenient objective function by means of the introduction of an overall performance index, identified as the hydrogen recovery yield. Therefore, the analysis proposed in the present paper shows that the reactive/permeative stage distribution has to be considered an important reactor design parameter, which can be opportunely modified to improve the performances of the process.     

Generating functions for Hurwitz-Hodge integrals

We describe explicit generating functions for a large class of Hurwitz-Hodge integrals. These are integrals of tautological classes on moduli spaces of admissible covers, a (stackily) smooth compactification of the Hurwitz schemes.Admissible covers and their tautological classes are interesting mathematical objects on their own, but recently they have proved to be a useful tool for the study of the tautological ring of the moduli space of curves, and the orbifold Gromov-Witten theory of DM stacks.     

Riemannian Submersions from Quaternionic Manifolds

In this paper we define the concept of quaternionic submersion, we study its fundamental properties and give an example.      

DNA supercoiling modeling of nucleosome and viral spooling

New kinematic equations are used to model DNA supercoiling. These equations govern the simultaneous production of multiple folding and coiling of a filament in space by diffeomorphism of a reference curve. Here we show how to use these equations to model regions of highly localized filament coiling, where mechanisms of proteic coding or viral spooling are important. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new stretch-twist-fold model for fast dynamo

Preliminary results on a new Stretch-Twist-Fold (STF) kinematic model for fast dynamo are presented. The evolution is prescribed by equations that govern the simultaneous stretching, writhing and coiling of a magnetic flux-tube by diffeomorphism of the initial circular configuration. Simple estimates based on minimized magnetic energy show that exponential growth of the magnetic field is indeed possible. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multipole expansions of the electrostatic molecular potential

Multipole expansions of the electrostatic molecular potential up to the hexadecapole terms are examined for H₂O, NH₃ and C₂H₄NH. A reasonable approximation to get unexpensive first order representations of the electrostatic potential for regions outside the van der Waals volume is found.     

Palladium(II)-catalyzed intramolecular 1,4-oxyacyloxylation of conjugated dienes. A stereocontrolled route to fused six-membered lactones and pyrans

Stereocontrolled palladium(II)-catalyzed intramolecular 1,4-oxidations of dienyl acids and alcohols proceed under mild conditions to give fused delta-lactones and pyrans, respectively, in good yields. The stereo- and regioselectivity was affected by the presence of LiCl and solvent composition (HOAc/acetone). The products obtained were used for further functionalizations using copper(I)-mediated reactions. Stoichiometric reactions of preformed dibutylcyanocuprates with pyrans containing an allylic acetate gave cis- and trans-fused ring systems with high gamma-selectivity and in high yields.