Chiral acetylenes as synthetic intermediates—II: Optically active 1,4-dialkylbuta-1,3-dienes: synthesis and conformational studies

The synthesis and the physical properties of some optically active 1,4-dialkylbuta-1,3-dienes are reported. The synthetic processes employed were essentially stereospecific. NMR, UV and CD spectra of these compounds provide information on the main conformation of the conjugated diene system, which was shown to be s-trans planar.     

Diisopropylethylamine: An effective catalyst for the introduction of the t-butyldimethylsilyl group

The rapid reaction of t-butyldimethylchlorosilane with alcohols catalysed by diisopropylethylamine at room temperature gave high isolated yields of the t-butyldimethylsilyl ethers.     

Sulle funzioni di più variabili a variazione limitata

Memoria presentata da G. Fichera     

Solution structures and dynamic behaviour of some iron chalcogen derivatives

Summary ¹³C-n.m.r. spectra of (-SR)₂Fe₂(CO)₆, (-SR)₂Fe₂(CO)₅P(n-Bu)₃ and (-X)₂Fe₂(CO)₆ (X=S or Se) show that the solid state structure is maintained in solution. N.m.r. evidence indicates that two isomeric species, not separable by means of the usual physicochemical methods, are present for (-SPh)₂Fe₂(CO)₆ with an overwhelming predominance of theanti form. The phosphine substitutes a COtrans to the iron-iron bond. For any of the iron chalcogen derivatives examined, variable temperature¹³C-n.m.r. spectra show that carbonyl exchange occur in one step. The energy barrier for the exchange of carbon monoxide in the phosphine derivative is lower than that in the unsubstituted complex.     

Characterization of raw and stabilized waste in relation to toxic metals mobility in realistic landfilling scenarios

Toxic metal release in simple leaching tests has been studied in this paper to assess waste behaviour in realistic landfilling scenarios. The waste is a galvanic sludge, raw or cement stabilized. Six different leachants were taken into account: distilled water, CO2-saturated solution, Olsen solution, Mehlich No. 3 solution, acid or alkaline soil circulating solution. Dynamic leaching tests of different duration were used for raw and stabilized waste. The results have shown that, with the exception of Mehlich No. 3 solution, when the waste comes into contact with waters of composition similar to that of the solutions studied, the potential environmental contamination should not be of concern.     

Su alcune formule in termini finiti per la risoluzione numerica dell’equazione di Poisson

Sommario Sono presentate diverse formule, di ordine elevato, che approssimano l'operatore di Laplace e che sono particolarmente vantaggiose quando vengono impiegate per la soluzione numerica della equazione di Poisson in due dimensioni.

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In this paper some high-order difference approximations to Poisson's equation in two dimensions are given It is shown that many formulas are available for practical calculations; their appropriate use associated with the process of repeating the solution on a finer mesh is a faster and more accurate method of improving the numerical solution.

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Lavoro eseguito nell'ambito del Consiglio Nazionale delle Ricetche.