Application of direct nonlinear regression from single TG curve to compounds undergoing simple and complex thermal decompositions

Nonlinear regression of the basic kinetic equation was used to determine kinetic parameters of simple and complex decomposition processes related to some pesticides and pharmaceutical substances. The method for this calculation was carried out using a single TG curve. These values were compared with those obtained with model‐fitting and model‐free methods. Nonlinear regression method is able to define a single mechanism for compounds undergoing one or few steps of decomposition processes. For compounds that undergo many steps of decomposition processes, only the mechanisms of some of them can be hypothesized. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 611–622, 2003     

Paniceins,unusual aromatic sesquiterpenoids linked to a quinol or quinone system from the marine sponge Halichondria panicea

Five new substances, panicein-A, -B₁, -B₂, -B₃ and C, containing an aromatic sesquiterpenoid moiety linked to a quinol or a quinone system, have been isolated from the sponge Halichondria panicea. The structures of these compounds were elucidated from their chemical and spectral properties.     

Nitrone cycloadditions to 2,3-dihydro-1-phenyl-1H-phosphole 1-oxide. Double asymmetric induction and kinetic resolution by a chiral nitrone

The cycloadditions of nitrones with 2,3-dihydro-1-phenyl-1H-phosphole 1-oxide give a single cycloadduct deriving from a highly diastereoselective approach of the nitrone anti to the phenyl ring of phospholene oxide. When the chiral gliceraldehyde derived nitrone is used, only two diastereoisomers are produced in 1.7:1 ratio. The structural assignment based on NMR data and X-ray analysis of the major isomer established a trans C3–C4 stereochemistry (derived from endo TS with respect to nitrone) and a C3–C4′ relative stereochemistry of threo type in the major isomer and erythro in the minor one. Therefore, each enantiomer of phospholene oxide 6 gives exclusively one cycloadduct with five contiguous stereogenic centres in an established and predictable absolute configuration. The difference of reactivity of the two enantiomers allowed a partial kinetic resolution of the racemic phospholene oxide, affording (+)-(S) enantiomer with 90% enantiomeric excess.     

Disidein,a pentacyclic sesterterpene condensed with an hydroxyhydroquinone moiety,from the sponge Disidea pallescens

A novel pentacyclic saturated sesterpene condensed with hydroxyhydroquinone moiety, which we named disidein (1), has been isolated from the marine sponge Disidea pallescens as disulfate sodium calcium salt. A minor accompaining compound, which seems a likely precursor of disidein, has been identified as 2-pentaprenylbenzoquinone (7).     

The electronic structure of SiO2, GeO2 and intermediate SixGe1−xO2 compositions: experiment and theory

Theoretical calculations are reported for SiO₂, GeO₂ and the intermediate composition Si_.5Ge_.5O₂ which reproduce the main observed features and trends in experimental photoemission spectra. The agreement between the two establishes the importance of band theory in understanding the electronic structure of these materials, and demonstrates that detailed quantitative predictions are feasible for such complex materials in terms of the empirical tight-binding method. The calculations further establish that the structure in the valence bands is determined mainly by nearest- neighbor oxygen-oxygen interactions.     

Synthesis of 3,4,6-trisubstituted cinnolines by intramolecular wittig reaction of ortho-carbonyl substituted arylazomethylenetriphenylphosphoranes

This paper reports the first example of Wittig reaction on arylazomethylenetriphenylphosphoranes, producing the new cinnolines 6 and 7 . A new unexpected rearrangement reaction producing quinoline 8 is also reported. The structure of compound 8 was determined by X-ray analysis.     

On the onset of chaotic motion in terms of generalized Langevin equations

New theoretical insights into the generalized Langevin approach to the onset of chaos are given. To make it possible to compare theory with “experiments” a fast computer algorithm is set up.