Molecular conformation of cyclenes: Part VI. Cycloalkatrienes with seven to ten carbon atoms in the ring

The strain energy of cycloalkatrienes with seven to ten carbon atoms in the ring is calculated as a function of various geometrical parameters. The most stable conformations are the boat for 1,3,5,cycloheptatriene and 1,3,5,cyclooctatriene, the all-cisC₂ for 1,3,6,cyclooctatriene, the boat-chair for 1,3,5, cyclononatriene, the all-cis crown for 1,4,7,cyclononatriene, a cis-trans-cis form for 1,3,5,cyclodecatriene, a cis-cis-trans and a trans-cis-cis conformer for 1,3,7, and 1,4,8,cyclodecatriene respectively. Some interconversion barriers are also discussed and compared with available experimental data. Fair agreement is generally found.     

Digital simulation of electrochemical processes involving very fast chemical reactions : Part 1. A simple general approach

A simple approach based on the steady-state assumption and linear concentration profiles in the reaction layer is proposed to simulate electrochemical systems involving very fast homogeneous chemical reactions. The flux equations are derived in detail and the method is shown to be suitable for catalytic e.c.e and dimerization reaction mechanism. The accuracy of the proposed method is checked by comparing the results obtained with those already available in the literature.     

Topology and phase transitions: paradigmatic evidence

We report upon the numerical computation of the Euler characteristic chi (a topologic invariant) of the equipotential hypersurfaces Sigma(v) of the configuration space of the two-dimensional lattice varphi(4) model. The pattern chi(Sigma(v)) versus v (potential energy) reveals that a major topology change in the family Sigma(v)(vinR) is at the origin of the phase transition in the model considered. The direct evidence given here-of the relevance of topology for phase transitions-is obtained through a general method that can be applied to any other model.     

An Easy Access to Furan-Fused Polyheterocyclic Systems

Nitrostilbenes characterized by two different or differently substituted aryl moieties can be obtained from the initial ring-opening of 3-nitrobenzo[b]thiophene with amines. Such versatile building blocks couple the well-recognized double electrophilic reactivity of the nitrovinyl moiety (addition to the double bond, followed by, e.g., intramolecular replacement of the nitro group) with the possibility to exploit a conjugated system of double bonds within an electrocyclization process. Herein, nitrostilbenes are reacted with different aromatic enols provided by a double (carbon and oxygen) nucleophilicity, leading to novel, interesting naphthodihydrofurans. From these, as a viable application, aromatization and electrocyclization lead in turn to valuable polycondensed, fully aromatic O-heterocycles.     

Absence of Critical Mass Densities for a Vibrating Membrane

We study the dependence of the eigenvalues of a N-dimensional vibrating membrane upon variation of the mass density. We prove that the elementary symmetric functions of the eigenvalues depend real-analytically on the mass density and that such functions have no critical points with constant mass constraint. In particular, the elementary symmetric functions of the eigenvalues, hence all simple eigenvalues, have no local maxima or minima on the set of those mass densities with a prescribed total mass.     

Chromium removal from water using LTA zeolites: effect of pH

The effect of pH changes on the ability of the synthetic zeolite NaA to remove Cr(3+) from water by ion exchange was investigated. The exchange rate was improved by working near neutrality. Despite of the occurrence of simultaneous adsorption, precipitation or cation exchange phenomena, spectroscopic analyses of samples taken at different contact times suggested the presence of an unique chromium environment in the solid phase. The increase in pH observed during the ion exchange favored polymerization-precipitation of chromium species present in solution, which, in turn, improved the metal removal capacity of zeolite NaA above the values expected for a pure cationic exchange reaction.     

Synthesis and anti‐staphylococcal activity of new halogenated pyrroles related to Pyrrolomycins F

The chemical synthesis of new halogenated pyrroles related to pyrrolomycins F is described and the anti‐staphylococcal activity compared. The replacement of 4′‐bromo atom of parent compounds with two chloro atoms at 3′ and 5′ position increase the antibacterial activity against a reference strain of S. aureus.     

Determination of the absolute configuration of a chiral oxadiazol-3-one calcium channel blocker, resolved using chiral chromatography, via concerted density functional theory calculations of its vibrational circular dichroism, electronic circular dichroism, and optical rotation

The chiral oxadiazol-3-one 2 has recently been shown to exhibit myocardial calcium entry channel blocking activity, substantially higher than that of diltiazem. To determine the enantioselectivity of this activity, the enantiomers of 2 have been resolved using chiral chromatography. The absolute configuration (AC) of 2 has been determined by comparison of density functional theory (DFT) calculations of its vibrational circular dichroism (VCD) spectrum, electronic circular dichroism (ECD) spectrum, and optical rotation (OR) to experimental VCD, ECD, and OR data. All three chiroptical properties yield identical ACs; the AC of 2 is unambiguously determined to be S(+)/R(-).     

Oxidative nucleophilic substitution of hydrogen versus ring-opening in the reaction of 4-R-2-nitrothiophenes with amines. The crucial effect of 4-alkyl groups

4-Alkyl-2-nitrothiophenes [10: R = CH3, CH(OH)CH3, CH(OCH3)CH3] react with secondary aliphatic amines, in the presence of AgNO3, to give 3-alkyl-2-amino-5-nitrothiophenes (12) through an oxidative nucleophilic substitution of hydrogen (ONSH) of synthetic interest. This behavior is in striking contrast with that of the parent 2-nitrothiophene (6), which was found to undergo ring-opening in analogous reaction conditions. A possible rationale for the crucial effect of alkyl groups is suggested, grounded also on a study of the corresponding Meisenheimer-like adducts.