摘要:

A wide range of CuNiNaY andCuNiKY zeolites were prepared by ion exchange. The location of both Ni2+and Cu2+cations within the zeolite framework was monitored after various stages of thermal treatment and the reduction process of the transition metal ions in a flowing hydrogen atmosphere was investigated and correlated with reduction time and temperature. The metallic phase generated on reduction was characterized by X-ray diffraction line broadening. The catalytic activity of the reduced zeolites in the hydrogenation of benzene is discussed in the light of these physical characterizations.Keywords: zeolites, supported Ni/Cu bimetals, cation location, crystallite size, catalysis.

ISSN:0008-4042    

DOI:10.1139/v90-225

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The electronic effects of a series of 18 heterocyclic carboxaldehydes (furans, thiophenes, pyrroles, and pyridines) have been studied by means of the correlation existing between13C chemical shifts of the carbonylic carbon and calculated total and π charges (AM1). The implications of this theoretical model to explain polar and resonance contributions to the total electronic effect are discussed.Keywords: heterocyclic substituents, electronic effects,13C NMR, DSP models.

ISSN:0008-4042    

DOI:10.1139/v90-226

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The possible thione–thiol tautomerism of 2- and 4-mercaptopyridines, 2-mercaptopyrimidine, and 4,6-dimethyl-2-mercaptopyrimidine in solution is studied by means of absorption (UV–VIS) spectroscopy. In accordance with earlier observations, polar solvents and self-association shift the apparent tautomeric equilibrium significantly towards the thione form. In dilute solutions of nonpolar solvents the thiol form predominates. On standing, significant changes are observed in the absorption spectra of these tautomeric compounds in ethanol, dioxane, and water. The time course of the tautomerization, followed spectrophotometrically, reveals quantitative transformation of the thiol form to the corresponding symmetrical disulfides. The influence of concentration, temperature, and irradiation with indirect sunlight are discussed. This thione–disulfide process is reversible in water, starting either from the tautomeric thione or from its symmetrical disulfide, implying a possible importance in biological systems.Keywords: thione–thiol tautomerism, absorption spectra, thiol–disulfide oxidation, mercaptopyridines and pyrimidines.

ISSN:0008-4042    

DOI:10.1139/v90-227

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

NMR line splitting under a strong static electric field (EF-NMR) allows one to measure the average alignment (second spherical harmonic) of the molecule studied under the influence of the field. This average alignment (per unit squared field) can be formulated theoretically by an expression involving the permanent dipole moment, the anisotropy of the static polarizability, etc. and possibly orientational intercorrelations within the liquid. On the other hand the Kerr constant per molecule can be represented by thesameexpression, multiplified by a factor that is independent of anystaticelectrical property of the molecule (for a gas this factor would be simply proportional to the anisotropy of theopticalpolarizability). Consequently the ratio of the above experimental results contains information bearing only on the optical properties. The formalism of the "tensor of polarizability increment" developed by the author for liquids made up of ellipsoidal molecules is employed. It is shown that by combining the above ratio with the constitutive equation for the refractivity of the liquid, the two distinct principal elements of the tensor of polarizability increment of the symmetric top molecules constituting the liquid are immediately obtained. Using then the molecular volume, a van der Waals estimate for the elongation of the molecule, and the index of refraction of the liquid, one can calculate the elements of the optical polarizability tensorinvacuo. The method is illustrated by neat acetonitrile for which the necessary experimental data exist in the literature. One finds, in units 1040 C2 m2 J−15.06 for the mean polarizability and 2.52 for its anisotropy. A published experimental study using depolarized light scattering in the gas phase indicates that the corresponding figures are 4.96 and 2.49 respectively at λ = 633 nm. Finally and accessorily, it is suggested that dipolar intercorrelations are weak in acetonitrile. Indeed, using an analogous formalism for the static permittivity of the liquid, a value for the permanent moment of the molecule is deduced. This value is within 1% of the experimental gas value.Keywords: polarizability tensors, liquids, Kerr constant, NMR.

ISSN:0008-4042    

DOI:10.1139/v90-228

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Zinc metal reacts with excess 3,5-dimethylpyrazole (Hdmpz) in the presence of O2to produce materials of composition Zn(dmpz)2(Hdmpz)y. Thermolysis of these materials results in the loss of Hdmpz and the formation of the [Zn(dmpz)2]xpolymer. Under appropriate conditions the pure dimer [Zn2(dmpz)4(Hdmpz)2] can be obtained in high yield. Crystals of bis[μ-(3,5-dimethylpyrazolyl-N1,N2)]bis[(3,5-dimethylpyrazolyl)(3,5-dimethylpyrazole)zinc(II)] are orthorhombic,a = 17.009(2),b = 29.239(2),c = 13.590(2) Å,Z = 8, space groupFddd. The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures toR = 0.037 andRw = 0.042 for 913 reflections withI ≥ 3σ(I). The structure of [Zn2(dmpz)4(Hdmpz)2] contains nearly planar doubly dmpz bridged Zn2units capped at each end by strongly hydrogen-bondedunits. The zinc atoms display pseudotetrahedral coordination geometry with Zn—N = 1.991(3) (bridging) and 2.025(3) Å (terminal), and N—Zn—N = 99.6(2)–113.8(2)°.Keywords: zinc 3,5-dimethylpyrazolate complexes, crystal structure.

ISSN:0008-4042    

DOI:10.1139/v90-229

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The kinetics of oxidation of potassium iodide by hydrogen peroxide in aqueous perchloric acid has been studied both in the absence and in the presence of sodium molybdate by means of the initial-rates method. The law found for the total initial reaction rate isThe activation energies associated with rate constantsk1,k2, andk3are 52 ± 1, 49 ± 1, and 42 ± 3 kJ mol−1, respectively. A mechanism in agreement with the experimental kinetic data is proposed, according to which rate constantsk1,k2, andk3correspond to the oxidations of iodide ion by H2O2, H3O2+and H2MoO5, respectively.Keywords: catalysis, hydrogen peroxide, iodide ion, kinetics, molybdate ion.

ISSN:0008-4042    

DOI:10.1139/v90-230

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

During the epoxidation of ethylene using ironmeso-tetrakis(2,6-dichlorophenyl)porphyrin chloride and iodosopentafluorobenzene severalN-alkylporphyrins were formed. The major product was 21-carboxymethyl-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin. This was derived, by oxidation, from the corresponding 21-formylmethyl complex which in turn was obtained from the initially formedN-hydroxyethylporphyrin, a compound not isolated due to its ready oxidation.Keywords:N-alkylporphyrins, suicide labelling, cytochrome P-450, hemin catalysis, epoxidation, oxidation.

ISSN:0008-4042    

DOI:10.1139/v90-231

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Electric field induced changes in the optical absorption spectra (electrochromism) have been used to obtain the excited state dipole moments and polarizabilities of styrene, 2-vinylnaphthalene, 2-naphthylacetylene, and 9-vinylanthracene. Excited state dipole moments of the order of 4–6 debye have been obtained for all these molecules except for 9-vinylanthracene, for which the excited state dipole moment is zero within experimental error. These results support earlier proposals of the involvement of charge transfer excited states in the fast and efficient acid-catalysed photohydration reactions of this type of substrate. 9-Vinylanthracene, on the other hand, under similar conditions reacts differently to give a dimer as the major photoproduct, and its reaction is not subject to acid catalysis. These results shed light on the importance of charge transfer excited states on the efficiency of photohydration reactions.Keywords: electrochromism, excited state, dipole moments, polarizabilities.

ISSN:0008-4042    

DOI:10.1139/v90-232

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

All-trans-retinal (1) was reacted withn-butylamine in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles in heptane to form all-trans-N-retinylidene–n-butylamine Schiff bases (2). The extent of protonation of2by 3-chloropropionic acid (CPA) to give3in AOT reverse micelles in heptane was found to depend on the ratio of [CPA] to [2], as well as on [H2O]/[AOT] (i.e., on the ω value). At any given [2] and ω values, increasing amounts of CPA increased the protonation and at any given constant [2] and [CPA], increasing ω values also increased the protonation. Over a period of 24 hours, there was only 4% decomposition of2in AOT reverse micelles in heptane at ω = 24. Conversely, in three hours, 23% of3decomposed in the same system. Thetranstocisphotoisomerization of2in heptane occurred at a much faster rate in the presence of AOT reverse micelles than in their absence. The appearance of carboxylate peaks (FTIR, 1400–1500 cm−1) indicated that the larger the AOT solubilized water pools, the greater the CPA dissociation.1also reacted with the α-NH2group ofl-lysine (4) in AOT reverse micelles in heptane to give the corresponding Schiff base6. Protonation of6occurred either intramolecularly or by reaction with unreacted4. These results were discussed in terms of rhodopsin protonations.Keywords: retinylidene Schiff bases, reverse micelles, protonation of Schiff bases,transtocisphotoisomerization.

ISSN:0008-4042    

DOI:10.1139/v90-233

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A method for the determination of dipole moment values based on Brot's theory is proposed. It takes into account the influence of the molecular anisotropies of shape and polarizability on the permittivity of a mixture. Starting from measurements performed on dilute solutions and from the knowledge of the molecular structure of some chlorinated derivatives of α-cyanostilbene and 1,3 derivatives of benzene, the best parameters of an ellipsoid used for the representation of a polar anisotropic molecule are determined. The dipole moments obtained, using benzene and tetrachloromethane as solvents, are finally compared to values from the literature.Keywords: dipole moment, Brot's formalism, molecular anisotropy.

ISSN:0008-4042    

DOI:10.1139/v90-234

出版商:NRC Research Press    

年代:1990

数据来源: NRC