Testing of a mathematical model for viscoelastic behaviour of poly-α-olefins using polyisobutene

The analytical model proposed for poly-α-olefins has been tested on polyisobutene. Relaxation modulus E(t) and distribution of relaxation times have been predicted from dynamic experiments and agree with literature data.     

Reactions SRN1 en serie heterocyclique: IV: Reactivite des sels du dimethyl-2,2 nitro-5 dioxanne-1,3

2-Alkyl 2-nitro 1,3-propanediol, 2-alkylidene 1,3-propanediol and 2-dialkylidene 1,3-propanediol are prepared via S_RN1 reactions with salts of 2,2-dimethyl 5-nitro 1,3-dioxane and acid-catalyzed cleavage of the resulting acetals.     

Etude cristallochimique de derives du chrome(0) : I. Structure cristalline et moleculaire du benzoate de methyle chrome dicarbonyle thiocarbonyle

The crystal and molecular structure of methylbenzoatechromium dicarbonyl thiocarbonyl has been determined by a single-crystal X-ray study. The compound crystallizes with two molecules in a unit cell of symmetry P$\text{1}$, with the following parameters: triclinic system, a = 7.108(3), b = 10.340(4), c = 8.523(3) Å; α = 89.75(6), β = 95.89(4), γ = 105.50(4)°; V = 601 ų; d_m = 1.57 ± 0.05, d_c = 1.56. The structure has been refined to R and R″ values of 0.030 and 0.038 respectively, for 1963 independent reflections. The main feature of the molecule is the C_s symmetry of the Cr(CO)₂CS group with a CrC(S) bond length of 1.792(2) Å, shorter than the CrC(O) bond length, mean: 1.849(3) Å.     

Biamperometric end-point detection with quinhydrone electrodes in coulometric neutralization titrations in nonaqueous media

Some new possibilities for continuous coulometric titration of bases, alone and in mixture, as well as of mineral acids, alone and in mixture, were investigated with acetic anhydride-anhydrous acetic acid as solvents. The titration end point was determined biamperometrically. It was established that quinhydrone electrodes with platinum, palladium, and gold as the metal phase can be equally satisfactorily applied to the end-point determination of both the titrations of bases or acids alone, and of their two-component mixtures. Amounts of 6–10 μequiv. of bases, i.e., 20–47 μequiv. of mineral acids, were determined with the maximal average deviation of 1.4%. Results of biamperometric determinations of bases are compared to those of catalytic thermometric determinations, while those of acids are compared with the results of photometric titrations. The agreement between the methods is satisfactory.     

Gas-phase acidity of D-glucose. A density functional theory study

The gas-phase acidity of D-glucopyranose was studied by means of B3LYP calculations combined with 6-31G(d,p) or 6-31+G(d,p) standard basis sets. For each anomer, deprotonation of the various primary and secondary hydroxyl groups was considered. As in solution, the anomeric hydroxyl is found to be the most acidic for both anomers, but only when the 6-31+G(d,p) basis set is used for geometry optimization. Deprotonation of the anomeric hydroxyl induces an important C(1)--O endocyclic bond elongation and subsequently promotes an energetically favored ring-opening process as attested by the very small calculated activation barriers. The results also suggest that interconversion between the various deprotonated alpha- and beta-anomers may easily occur under slightly energetic conditions. B3LYP/6-311+G(2df,2p) calculations led to the an absolute gas-phase acidity of deltaacidGo(298)(alpha-D-glucose) = 1398 kJ mol(-1). This estimate matches well the only experimental value available to date. Finally, this study again confirms that the use of diffuse functions on heavy atoms is necessary to describe anionic systems properly and to achieve good relative and absolute gas-phase acidities.     

On the relationship between the structures of Cu(II) complexes and their chemical transformations

The paper deals with the relationship between the crystal and molecular structures of CuSO₄.5 H₂O, CuSO₄.3 H₂O and CuSO₄.H₂O on the one hand, and the stoichiometries of their thermal decompositions on the other. With the use of methods of X ray powder diffractograms, i.r. and electronic spectra, evidence is provided that the intermediates of the thermal decomposition of CuSO₄.5 H₂O have the same crystal and molecular structures as CuSO₄.3 H₂O and CuSO₄.H₂O prepared by other procedures. It is also shown that at temperatures near that of the thermal decomposition, certain, not further identified structural changes take place in CuSO₄.5 H₂O.

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Zusammenfassung Es wird einerseits der Zusammenhang der Kristall- und Molekularstruktur von CuSO₄ · 5H₂O, CuSO₄ · 3H₂O und CuSO₄ · H₂O behandelt und andererseits die Stöchiometrie ihrer thermischen Zersetzung. Mit der Auswertung der Röntgen-Pulverdiffraktogramme, der IR- und Elektronenspektren wurde der Beweis erbacht, da\ die Zwischen-produkte der thermischen Zersetzung von CuSO₄ · 5H₂O dieselben Kristall- und Molekül-strukturen besitzen, wie auf anderen Wegen hergestelltes CuSO₄ · 3H₂O bzw. CuSO₄ · H₂O. Ferner wurde gezeigt, da\ bei Temperaturen in der NÄhe der thermischen Zersetzungstemperatur gewisse, jedoch noch nicht identifizierte StrukturÄnderungen in dem CuSO₄ · 5H₂O stattfinden.

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Résumé L'article examine la corrélation entre les structures cristallines et moléculaires de CuSO₄.5 H₂O, CuSO₄.3 H₂O et CuSO₄.H₂O d'une part et la stoechiométrie de leur décomposition thermique de l'autre. En se servant des méthodes des diffraction des rayons X sur poudre et des spectres infra-rouges et électroniques on montre que les produits intermédiaires de la décomposition thermique de CuSO₄.5 H₂O ont les mÊmes structures cristallines et moléculaires que celles de CuSO₄.3 H₂O et de CuSO₄.H₂O préparées par d'autres procédés. On montre également qu'à des températures proches de celle de la décomposition thermique de CuSO₄. 5H₂O des changements structuraux non encore identifiés ont lieu.

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uSO₄ · 5₂, uSO₄ · ₂ uSO₄ · ₂, — . , , , uSO₄ · 5₂ uSO₄ · ₂ uSO₄ · ₂, . , , uSO₄, · 5₂ , .

     

Straightforward three-component synthesis of diarylmethylpiperazines and 1,2-diarylethylpiperazines

Several functionalized diarylmethylpiperazines and 1,2-diarylethylpiperazines have been synthesized in moderate to high yield according to a one-step three-component coupling between an aromatic or a benzylic organozinc reagent, a piperazine derivative, and an aromatic aldehyde. The procedure can be extended to the synthesis of benzylpiperazine derivatives or β-arylethylpiperazines toward the use of paraformaldehyde or aliphatic aldehydes.     

Caractérisation de peroxofluorotantalates(V). Mise en évidence d'isomères géométriques par résonance magnétique nucléaire (19F et 1H)

A series of tantalum(V) peroxofluoro complexes of the type Et₄N{Ta(O-O)-F₃(diket)} (diket = β-keto-enolate) has been prepared by the reaction of β-diketones with the new compound Et₄N{Ta(O-O)F₄(H₂O)}. The complexes have been characterised in the solid state on the basis of their analytical and infrared spectral data. When the bidentate chelating ligand is unsymmetrical, proton and fluorine nuclear magnetic resonance spectra demonstrate that the products exist as geometrical isomers in acetonitrile solutions.The orientation of the peroxo group according to the nature of the metal-ligand bonds is discussed.     

Generation and use of an equivalent of difluoroacetamide or difluoroacetate anions

Ethers of trifluoroacetaldehyde hemiaminals can undergo dehydrofluorination under basic conditions to provide ethers of difluoroketene hemiaminals. The latter behave as equivalents of difluoroacetamide or difluoroacetate anions towards various electrophiles, yielding a range of difluoromethylcarbonyl products.