Substituent effects in the Baeyer–Villiger reaction of acetophenones: a theoretical study

This paper reports the first complete theoretical study of substituent effects on the mechanism of the Baeyer– Villiger (BV) reaction in non‐polar solvents taking into account the lowest‐energy mechanism that has been proposed for this rearrangement which is non‐ionic and fully concerted. The BV reaction of p‐substituted acetophenones, p‐XC₆H₄COCH₃ (X = NO₂, CN, H, CH₃, OCH₃), with performic (PFA) and trifluoroperacetic (TFPAA) acids, catalyzed by formic (FA) and trifluoroacetic (TFAA) acids, respectively, using the MPWB1K functional and the 6‐311G(d,p) and 6‐311++G(d,p) basis sets, are studied. Solvent effects are taken into account by means of the PCM continuum model using dichloromethane as solvent. Electron‐donating substituents on the aryl group have a relatively small activation effect on the first step, but a pronounced activation effect on the second to the point of being able to change the rate‐determining step (RDS) of the reaction, as observed in the case of p‐methoxyacetophenone with TFPAA acids. After analyzing the changes in Gibbs free energy of activation, geometrical parameters, and charge distributions of the transition states (TSs), explanations are provided for the two distinct effects that substituents on the ketone have on the kinetics of the addition and migration steps of the BV oxidation. The effect of the acid/peracid pair used is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Karyotype differentiation patterns in species of the subfamily Scarabaeinae (Scarabaeidae, Coleoptera)

The aim of this study was to describe the karyotype of species belonging to the subfamily Scarabaeinae (Coleoptera, Scarabaeidae) and to compile the conventional cytogenetic data available in the literature for this group. The karyotypes of ten species belonging to the tribes Canthonini, Coprini, Onthophagini and Phanaeini were analyzed by conventional staining. Eight of these species were described for the first time (Canthon aff carbonarius, Canthon chalybaeus, Coprophanaeus dardanus, Deltochilum aff amazonicum, Dichotomius geminatus, Oxysternon silenus, Phanaeus chalcomelas and Malagoniella aff astyanax) and two were redescribed (Diabroctis mimas and Digitonthophagus gazella) since their karyotypes differed from those previously published in the literature. Four species studied showed a diploid number of 2n = 20 and a parachute type sex determining system and the karyotype was 2n = 20,Xy in two species and 2n = 18,Xy_p, 2n = 19,X0, 2n = 12,XY and 2n = 14,neoXY in one each. The chromosome morphology of the different species varied, with the observation of metacentric, submetacentric, subacrocentric and acrocentric chromosomes. The X chromosome was predominantly meta or submetacentric in the species analyzed, whereas the y chromosome presented two arms or was punctiform. In conclusion, the subfamily Scarabaeinae comprises 120 species analyzed cytogenetically, and are observed the occurrence of five chromosome rearrangements (autosome–autosome and X-autosome fusions, pericentric inversions, fissions and loss of the y chromosome) that are related to the chromosome variability and evolution in the group.     

Ileum of the Cephalotes ants: a specialized structure to harbor symbionts microorganisms

We conducted comparative morphological studies of the tract digestive of Cephalotes atratus, C. clypeatus and C. pusillus, aiming at describing the relationships among these three species, as well as the histochemical, enzymatic, and ultra-morphological differences of the wall and the contents of the digestive tract, therefore contributing for the understanding of the relationships between symbionts and their host.     

Mononukleare Kupfer(II)‐Komplexe von dioxaalkylenund alkylenverbrückten Bis‐isoharnstoffen

Mononuclear Copper(II) Complexes of Dioxaalkylene and Alkylene Bridged Bis‐isoureas By reaction of N‐benzoylthiocarbamic‐O,S‐diethylester with primary diamines (oxa)alkylene bridged isoureas 1 have been prepared. They yield with Cu^II neutral chelates 2 with tetradentate ligand coordination. The structures of the ligand 1 a and of the related Cu^II complex 2 a have been determined by X‐ray crystal structure analysis. They show an enamine tautomer in the ligand and a slightly tetrahedrally distorted coordination with an (oxa)alkylene bridge between the trans arranged N ligator atoms in the complex.     

To(Γ) phonons in GaAs under uniaxial strain

Using the density-functional theory in the local-density approximation, norm-conserving pseudopotentials, and plane-wave expansions, we have developed a simple way to calculate ab initio the uniaxial strain dependence of the TO(Γ) phonon mode in GaAs, including the envolved relaxations effects. The relaxation response of the system was evaluated from the use of the elasticity theory. Our results confirm the experimental evidence and show a reasonable agreement with the observed data for the frequency splitting of this phonon mode. © 1993 John Wiley & Sons, Inc.     

Magnetic susceptibilities of binary non-electrolyte mixtures

Molar magnetic susceptibilities are determined by theGouy method for the following four systems: dichloromethane + methyl acetate,n-pentane + dichloromethane,n-pentane + methyl acetate and 2-propanol +n-pentane, in whichn-pentane is a non-polar molecule and the other three are polar while 2-propanol is associated in its pure state. Excess diamagnetic susceptibilities are calculated to obtain information about possible interactions. Diamagnetic susceptibilities were related with molecular polarizabilities byBoyer-Donzelot's equation and compared with experimental results.

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Magnetische Suszeptibilitäten binärer Nicht-Elektrolyt-Mischungen

Zusammenfassung Für folgende vier Systeme wurden die molaren magnetischen Suszeptibilitäten mittels derGouy-Methode bestimmt: Dichlormethan + Methylacetat,n-Pentan + Dichlormethan,n-Pentan + Methylacetat, und 2-Propanol +n-Penten; dabei istn-Pentan ein nicht-polares Molekül, die anderen sind polar, wobei 2-Propanol zusätzlich Assoziation zeigt. Es werden Exzess-diamagnetische Suszeptibilitäten berechnet, um Informationen bezüglich möglicher Wechselwirkungen zu erhalten. Die diamagnetischen Suszeptibilitäten wurden mit den molekularen Polarisierbarkeiten über dieBoyer-Donzelot-Beziehung in Relation gesetzt und mit den experimentellen Resultaten verglichen.

     

Perfluoroalkanesulfonylimides and their lithium salts: synthesis and characterisation of intermediates and target compounds

ECF processes have been extensively experienced and developed since early 1970s at the Fluorine Chemistry Laboratory of Padua University: several classes of perfluorinated inert and functional compounds have been obtained, in particular perfluoro heterocyclics and perfluorinated acid fluorides.Recently the demand for electrolyte salts, applied in lithium batteries, drove our interest to investigate on the perfluoroalkanesulfonylimides.A series of the perfluoroalkanesulfonylfluoride precursors has been obtained by ECF and their metathesis to the related imides and lithium salts has been investigated.A number of representative products has been obtained and characterized in their structure and ionic conductivity.